Chapter 17: Varicella

Disease Description

Varicella (chickenpox) is a febrile rash illness resulting from primary infection with the varicella-zoster virus (VZV). Humans are the only source of infection for this virus. Varicella is characterized by a pruritic, maculopapular and vesicular rash usually with 250–500 skin lesions that evolves into noninfectious crusts over a 4- to 7-day period. While the initial lesions are crusting, new crops form; the simultaneous presence of skin lesions in various stages of evolution is characteristic of varicella.12

Varicella can occur in vaccinated persons (termed breakthrough varicella). Compared with varicella in unvaccinated persons, breakthrough varicella is generally milder, often with fewer than 50 skin lesions, fewer vesicles (sometimes only maculopapular lesions and no vesicles), low or no fever, and fewer days of illness.2 Given its modified clinical presentation, breakthrough varicella can be challenging for healthcare providers and parents to recognize clinically.

Varicella is generally a mild disease, but severe complications can occur in any age group.3456 Severity is increased among immunocompromised persons, pregnant women, children younger than one year of age, and adults.7 Severe complications include secondary bacterial infections (most notably those caused by group A beta-hemolytic Streptococcus, e.g., cellulitis, necrotizing fasciitis, septicemia, and toxic shock syndrome but also S. aureus), pneumonia, encephalitis, cerebellar ataxia, bleeding disorders, and Reye syndrome.7 Rarely, these complications may result in death.4 The potential for severe varicella exists among both vaccinated and unvaccinated persons.

Congenital varicella syndrome, characterized by cutaneous scarring in a dermatomal distribution, hypoplasia of an extremity, microcephaly, ocular and neurologic abnormalities, and low birth weight, may occur among 0.4%–2.0% of infants born to women who develop varicella during the first or second trimester of pregnancy.8910 Infants born to women who develop varicella within the period of five days before delivery to two days after delivery are at high risk of severe neonatal varicella.

Immunity following varicella is considered to be long-lasting and a second case of varicella in otherwise healthy person is uncommon.1112 However, second cases may occur more commonly among immunocompromised persons.13

After primary infection, VZV remains latent in the sensory-nerve ganglia and reactivates in approximately 1 in 3 of infected persons during their lifetime, resulting in herpes zoster (shingles).141516 Herpes zoster usually presents as a vesicular rash (appearing as clusters of vesicles) with pain and itching in a dermatomal distribution. Herpes zoster incidence increases with age, especially after age 50, and is more common among immunocompromised persons. A decline in the cell-mediated immunity is considered to be an important factor in the development of herpes zoster.

Transmission and infectious period

Varicella is highly infectious, with secondary infection occurring in 61%–100% of susceptible household contacts.1718192021 Transmission of VZV occurs from person to person by direct contact with the vesicular fluid of skin lesions of persons with either varicella or herpes zoster or inhalation of aerosols from vesicular fluid of skin lesions of persons with varicella or herpes zoster; spread from oropharyngeal secretions of persons with varicella, that also may be aerosolized, may occur but to a much lesser extent.

The incubation period for varicella is 10–21 days, most commonly 14–16 days. Persons with varicella are considered infectious from 1–2 days before the onset of rash until all lesions are crusted, typically 4–7 days after onset of rash. Vaccinated persons who get varicella may develop lesions that do not crust. These persons are considered contagious until no new lesions have appeared for 24 hours. Persons with herpes zoster are contagious while they have active, vesicular lesions (usually 7–10 days).

Background

Before the availability of varicella vaccine in the United States, almost everyone had varicella. Thus, the number of cases approximated the birth cohort, and in the early 1990s (the prevaccine era) this resulted in an average of about 4 million cases of varicella, 10,500–13,500 hospitalizations (range: 8,000–18,000), and 100–150 deaths each year.345 Varicella primarily affected children; approximately 90% of cases occurred before 15 years of age, with the highest incidence reported among children 1–4 years of age.32223

Varicella vaccine was licensed and has been recommended in the United States since 1995. A two-dose series is recommended, with routine administration of the first dose at 12–15 months of age and the second dose at 4–6 years of age.24 Vaccination of older children, adolescents and adults without evidence of immunity to varicella and persons who had received only one dose of vaccine is also recommended. The minimum interval between the doses is 3 months for persons younger than 13 years of age and 4 weeks for persons 13 years of age and older.

One dose varicella vaccination coverage among children 19–35 months of age reached 90% in 2007, stabilizing around at least 90% thereafter; ≥2-dose varicella vaccination coverage among adolescents 13–17 years of age without history of varicella was 92% in 2020.2526 Attaining and maintaining high vaccine coverage led to substantial declines in varicella morbidity and mortality in the United States. Overall, in 2018–2019, varicella incidence declined >97% based on data from four states that have continuously reported varicella to the National Notifiable Diseases Surveillance System (NNDSS) since before the varicella vaccination program.27 The second dose of varicella vaccine for children was added to the national program in 2007.24 During the 2-dose era, data from 39 states and DC have shown an 89% decline in varicella incidence.27 Incidence declined in all age groups with the greatest declines among children 5–14 years of age (92%–95%). As vaccination coverage has increased, about half of varicella cases now occur among vaccinated persons.

Similarly, the severe outcomes of varicella declined substantially. Compared with the pre vaccine years, by 2018–2019, varicella hospitalizations declined 90% and deaths with varicella as the underlying cause of death declined 89% for all ages.28 After 25 years of the varicella vaccination program, fewer than 1,400 hospitalizations and 18–30 deaths are occurring annually in the United States. The greatest decline for both hospitalizations and deaths (97% and >99%, respectively) was among persons <20 years of age, born during the varicella vaccination program, in whom these severe outcomes have been nearly eliminated.28

The varicella vaccination program has also substantially reduced the number of outbreaks in the U.S. Additionally, outbreak size and duration declined from a median of 15 cases per outbreak and 45 days duration early in the vaccination program to 7 cases and 30 days duration during the mature phase of the vaccination program.29 Elementary schools continue to be the most common sites for varicella outbreaks and are the main reporting sources for outbreak surveillance although the proportion of school outbreaks has decreased over time. Despite low susceptibility among adults (generally less than 5%), outbreaks have been reported from a variety of adult settings, including correctional facilities, hospitals, military training facilities, refugee centers, immigration detention facilities, homeless shelters, other residential institutions, and cruise ships.

Vaccination

For specific information about varicella vaccination, refer to the Pink Book varicella chapter which provides information on the varicella vaccines, vaccination schedule and use, contraindications and precautions, adverse events and reactions, and vaccine storage and handling.

Evidence of Immunity

Evidence of immunity to varicella includes any of the following:24

1.) Documentation of age-appropriate vaccination

• Preschool-aged children 12 months of age or older: 1 dose
• School-aged children, adolescents, and adults: 2 doses
  • For children younger than 13 years of age, the minimum interval between the 2 doses is 3 months. However, if the interval between the 2 doses was at least 28 days, the second dose is considered valid.
  • For persons 13 years of age or older the minimum interval between doses is 4 weeks (28 days).

2.) Laboratory evidence of immunity or laboratory confirmation of disease

• Commercial assays can be used to assess disease-induced immunity, but they lack sensitivity to always detect vaccine-induced immunity (i.e., they may yield false-negative results).

3.) Born in the United States before 1980

• For healthcare workers, pregnant women, and immunocompromised persons, birth before 1980 should not be considered evidence of immunity.

4.) A healthcare provider diagnosis of varicella or verification of history of varicella disease

• Verification of history or diagnosis of typical disease can be done by any healthcare provider (e.g., school or occupational clinic nurse, nurse practitioner, physician assistant, physician). For persons reporting a history of or presenting with atypical and/or mild cases, assessment by a physician or designee is recommended and either one of the following should be sought: a) an epidemiologic link to a typical varicella case or laboratory-confirmed case, or b) evidence of laboratory confirmation, if testing was performed at the time of acute disease. When such documentation is lacking, persons should not be considered to have a valid history of disease, because other diseases may mimic mild, atypical varicella.

5.) A healthcare provider diagnosis of herpes zoster or verification of history of herpes zoster

Laboratory Testing

As varicella disease has declined with the introduction of a vaccine, the need for laboratory confirmation has concomitantly grown because fewer physicians have seen varicella and breakthrough disease is often milder with fewer lesions and may lack characteristic vesicles. Laboratory confirmation of suspected varicella is becoming increasingly necessary to inform clinical and public health management and understand the true burden of disease and is now routinely recommended. The preferred diagnostic test to confirm varicella is detection of viral DNA by real-time PCR.

For additional information on laboratory disease surveillance, including specific instructions for specimen collection and shipping, see Chapter 22, Laboratory Support for Surveillance of Vaccine-Preventable Diseases. For any other questions regarding laboratory testing, varicella contacts are listed in Table 1.

Importance of Rapid Case Identification

Reporting varicella cases in childcare centers, schools, other institutions, military barracks, and other group settings will facilitate public health action and outbreak control. A single case should trigger intervention measures because it could lead to transmission and outbreaks. In addition, in certain high-risk settings (e.g., hospitals and other healthcare settings, schools that may have students who are immunocompromised), rapid case identification and public health action are important to prevent infection of susceptible persons at high risk for serious complications of varicella, such as immunocompromised persons and pregnant women, for whom varicella vaccine is contraindicated.24

Importance of Surveillance

Varicella surveillance helps to facilitate public health actions at the state and local level and to monitor the impact of the varicella vaccination program. Specifically, surveillance data are needed to:

• document and monitor the impact of the vaccination program on disease incidence, morbidity, and mortality;
• characterize and understand changes in the burden of disease;
• characterize populations requiring additional disease control measures;
• detect and respond to outbreaks;
• evaluate the effectiveness of prevention strategies; and
• assess for waning of immunity.

Case Definition

The following case definitions were approved by the Council of State and Territorial Epidemiologists (CSTE) for varicella cases in June 202330 and for varicella deaths in 1998.31

Criteria for case classification:

Clinical Criteria

In the absence of a more likely alternative diagnosis:

• An acute illness with a generalized rash with vesicles (maculopapulovesicular rash),

OR

• An acute illness with a generalized rash without vesicles (maculopapular rash).

Laboratory Criteria*^a

Confirmatory Laboratory Evidence:

• Positive polymerase chain reaction (PCR) for varicella-zoster virus (VZV) DNA, ^b,c

OR

• Positive direct fluorescent antibody (DFA) for VZV DNA,

OR

• Isolation of VZV,

OR

• Significant rise (i.e., at least a 4-fold rise or seroconversion^d) in paired acute and convalescent serum VZV immunoglobulin G (IgG) antibody. ^c,e

Supportive Laboratory Evidence:

• Positive test for serum VZV immunoglobulin M (IgM) antibody. ^c,f

* Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

^a A negative laboratory result in a person with a generalized rash with vesicles does not rule out varicella as a diagnosis.

^b PCR of scabs or vesicular fluid is the preferred method for laboratory confirmation of varicella. In the absence of vesicles or scabs, scrapings of maculopapular lesions can be collected for testing.

^c Not explained by varicella vaccination during the previous 6–45 days.

^d Seroconversion is defined as a negative serum VZV IgG followed by a positive serum VZV IgG.

^e In vaccinated persons, a 4-fold rise may not occur.

^f IgM serology has limited value as a diagnostic method for VZV infection and is not recommended for laboratory confirmation of varicella. However, an IgM positive result in the presence of varicella-like symptoms can indicate a likely acute VZV infection. A positive IgM result in the absence of clinical disease is not considered indicative of active varicella.

Epidemiologic Linkage Criteria

Confirmatory Epidemiologic Linkage Evidence:

• Exposure to or contact with a laboratory-confirmed varicella case,

OR

• Can be linked to a varicella outbreak containing ≥1 laboratory-confirmed case,

OR

• Exposure to or contact with a person with herpes zoster (regardless of laboratory confirmation).

Presumptive Epidemiologic Linkage Evidence:

• Exposure to or contact with a probable varicella case that had a generalized rash with vesicles.

Healthcare Record Criteria

• Provider diagnosis of varicella or chickenpox but no rash description.

Varicella Case Classifications

Confirmed:

• Meets clinical evidence AND confirmatory laboratory evidence,

OR

• Meets clinical evidence with a generalized rash with vesicles AND confirmatory epidemiologic linkage evidence.

Probable:

• Meets clinical evidence with a generalized rash with vesicles,

OR

• Meets clinical evidence with a generalized rash without vesicles AND:
  • Confirmatory or presumptive epidemiologic linkage evidence, OR
  • Supportive laboratory evidence.

OR

• Meets healthcare record criteria AND:
  • Confirmatory or presumptive epidemiologic linkage evidence, OR
  • Confirmatory or supportive laboratory evidence

Varicella Death Classifications

Confirmed: A death resulting from a confirmed case of varicella which contributes directly or indirectly to acute medical complications that result in death.

Probable: A death resulting from a probable case of varicella which contributes directly or indirectly to acute medical complications that result in death.

Other definitions

Varicella-like rash in vaccine recipients: A varicella-like rash in a recently vaccinated person may be caused by either wild- or vaccine-type virus or have other etiologies. Approximately 4%–6% of 1-dose and 1% of 2-dose vaccine recipients, respectively, develop a generalized rash with a median of 5 lesions 5–26 days postvaccination, and 1%–3% develop a localized rash at the injection site with a median of 2 lesions 8–19 days postvaccination.32 The rash may be atypical in appearance (maculopapular with no vesicles). Attribution of disease to vaccine strain VZV can be done by distinguishing wild-type VZV from vaccine-strain VZV using strain differential PCR.

Breakthrough disease is a case of infection with wild-type VZV occurring more than 42 days after vaccination. Disease is usually mild with a shorter duration of illness, fewer constitutional symptoms, and generally fewer than 50 skin lesions. Breakthrough cases with fewer than 50 lesions have been found to be one-third as contagious as varicella in unvaccinated persons, but breakthrough cases with 50 or more lesions are as contagious as cases in unvaccinated persons.33 Though generally mild, about 25%–30% of breakthrough cases among 1-dose vaccinated children have clinical features more similar to those in unvaccinated children and rare, severe presentations with visceral dissemination have been reported.34 Persons who received two doses of vaccine are less likely to have breakthrough disease than those who received one dose.3536 Additionally, breakthrough varicella may be further attenuated among 2-dose vaccine recipients though the difference was not always statistically significant.2937 No cases of breakthrough varicella with visceral dissemination have been reported among 2-dose vaccinees.34

Reporting and Case Notification

Case reporting within a jurisdiction

Each state and territory has regulations or laws governing the reporting of diseases and conditions of public health importance.38 These regulations and laws list the diseases to be reported and describe the persons or institutions responsible for reporting, including healthcare providers, hospitals, laboratories, schools, childcare facilities, and other institutions. Persons reporting case(s) should contact their state health department for state-specific reporting requirements.

States not conducting case-based surveillance are encouraged to progressively implement individual case reporting integrating varicella surveillance into an existing system where feasible. This can be done by establishing statewide or sentinel surveillance. Statewide surveillance involves adding varicella to the list of notifiable diseases that are reported to the state health department. Sentinel site surveillance involves identifying sites such as schools, childcare centers, physicians' practices, hospitals, colleges, and other institutions to perform surveillance for varicella. Sentinel sites can be limited to a geographic area, such as a county or city, or selected to be representative of the entire state population. States may also consider requesting reports from sites that already participate in other surveillance networks. States can expand the number of sites as they develop their system with the intention of eventually having statewide surveillance.

Case notification to CDC

Notifications for confirmed or probable cases of varicella should be sent to CDC using event code 10030 through National Notifiable Diseases Surveillance System (NNDSS). Case notifications should not be delayed because of incomplete information or lack of confirmation. Data can be updated electronically as more information becomes available. The state in which the patient resides at the time of diagnosis should submit the case notification to CDC. If jurisdictions have questions about varicella reporting and case notification, please contact the Division of Viral Diseases, Viral Vaccine Preventable Diseases Branch at CDC.

Information to collect

The following are core and disease-specific data elements that are epidemiologically important and needed for varicella case classification and should be collected during case investigations. Please also refer to the Varicella Surveillance Worksheet for a complete list of the variables that should be collected during case investigations (Appendix 20). Additional information may be collected at the direction of the state health department.

In bold, are the critical variables used to monitor the impact of the varicella vaccination program.

• Demographic information
• Name
• Address
• Date of birth
• Age
• Sex
• Ethnicity
• Race
• Country of birth
• Reporting source
  • County
  • Earliest date reported
• Varicella vaccination status
  • Number of doses of varicella vaccine
  • Date(s) of vaccination
• Clinical data
  • Date of illness onset (note: this may be earlier than rash onset due to prodromal symptoms)
  • Date of rash onset
  • Duration of rash
  • Rash description
    • Whether the rash was generalized
    • Whether the rash had vesicles (maculopapulovesicular rash) or not (maculopapular rash)
    • No rash description and only a provider diagnosis of varicella
    • Number of lesions (to assess severity of disease)
      • Classified as: fewer than 50 lesions (actual number of lesions if <50 total lesions); 50–249 lesions; 250–499 lesions; 500 or more lesions
  • Complications
  • Pre-existing medical conditions
  • Medications
  • History of varicella (to document reported second infections)
• Outcome (patient survived or died)
  • Hospitalization
    • Duration and reason for hospitalization, if known
  • Death
    • Date of death
    • Postmortem examination results
    • Death certificate diagnoses
• Laboratory information
  • Laboratory tests performed: indicate test type, dates, and results
• Epidemiologic data
  • Transmission setting
  • Source of transmission (contact with a person with varicella or herpes zoster, and whether they were laboratory-confirmed)
  • Association with a varicella outbreak and whether there was at least one laboratory-confirmed case

Varicella deaths reporting

In 1998, CSTE recommended that varicella-related deaths be placed under national surveillance, and varicella-related deaths became nationally notifiable on January 1, 1999.31

Varicella deaths can be identified through death certificates, which may be available through state vital records systems and may be more readily available soon after death in states using electronic death certificates. State public health departments may also request that local health departments, healthcare practitioners, and hospitals report varicella deaths that occur in their community.

Because varicella is a vaccine-preventable disease, all deaths due to varicella should be investigated. Investigation may provide insight into risk factors for varicella mortality and may help identify missed opportunities for, and barriers to, vaccination. A worksheet is provided to guide varicella death investigations (see Appendix 19). Deaths should be reported to the CDC National Center for Immunization and Respiratory Diseases, Division of Viral Diseases, Viral Vaccine Preventable Diseases Branch and to NNDSS.

Case Investigation and Management

All patients with suspected varicella should be investigated. A single case should trigger intervention measures because it could lead to transmission and outbreaks. Clinical diagnosis of varicella can be unreliable. Cases of suspected varicella should be laboratory confirmed. Laboratory confirmation of varicella is important as varicella may present with mild or atypical presentation making clinical diagnosis especially challenging.

Patients with varicella should self-isolate at home until no longer infectious, unless medical care is needed (all lesions have crusted or, if no vesicles were present, when no new lesions appear within a 24-hour period). For residential institutions and healthcare settings, patients should be immediately isolated in a closed-door room (negative pressure room if available) until they are no longer infectious; staff with varicella should be excluded from the setting and self-isolate until no longer infectious.

As part of the case investigation, the potential for further transmission should be evaluated, and contacts of the patient during the infectious period should be identified. Guidance can be found in the Outbreak Investigation section.

Outbreak Control and Investigation

These recommendations include prior guidance published in the document Strategies for the Control and Investigation of Varicella Outbreaks Manual, 2008, which has been retired.

An outbreak of varicella is defined as the occurrence of ≥3 varicella cases that are related in place and are epidemiologically linked.

Confirmation of the Outbreak

• The first step in the control and investigation of a suspected varicella outbreak is to confirm the outbreak. Physicians and public health professionals should make every effort to establish epidemiologic links for cases and obtain specimens for laboratory testing.
• Laboratory confirmation of varicella is recommended. In larger outbreaks, try to confirm at least three to five cases (irrespective of the patients' vaccination status), especially at the beginning of the outbreak. Laboratory confirmation is also helpful to assess the end of the outbreak.

Notification of the Outbreak

• Notification of an outbreak of varicella and increasing awareness in the affected setting or community is an important step for controlling the outbreak.
• Local or state health departments should be notified by schools or healthcare providers when cases of varicella are identified. Other healthcare providers in the community should also be notified of the outbreak by the local or state health departments, asked to report varicella patients they consult with in the office or by phone, and collect specimens to confirm the disease.
• As part of the notification, a fact sheet with information about the signs and symptoms of varicella, complications from the disease, and basic facts about the vaccine can be provided to both parents and healthcare providers (See Related Pages)

Case Identification and Management

• Once an outbreak of varicella is confirmed, the affected population should be surveyed to identify all cases.
• Case finding is an important step for outbreak control and can be done concurrently with implementing control measures.
  • A template for a varicella outbreak line list can be found here: Varicella Outbreak Surveillance.
• See above recommendations for Case investigation and management.
• Cases and outbreaks should be reported to the local/state health department.

Management of Contacts

• During the case investigations, public health officials should identify exposed persons (contacts of the patients with varicella during the infectious period).
• A notification letter can be sent to those who may have been exposed to recommend that they check for evidence of immunity and receive appropriate post-exposure prophylaxis (PEP).
  • Exposed persons who are unvaccinated and without other evidence of immunity should receive their first varicella vaccination within five days of exposure (within three days optimal).
  • High risk contacts without evidence of immunity are recommended to receive varicella zoster immunoglobulin (Varizig), ideally within 96 hours but up to 10 days postexposure.
• Exclusion of contacts
  • Vaccinated or have other evidence of immunity (e.g., IgG positive): no exclusion or restrictions are recommended for contacts vaccinated with the first dose within 5 days post-exposure, or who previously received ≥1 dose vaccine.
  • Unvaccinated and without other evidence of immunity: exclude from the outbreak settings from day 8 to 21 after exposure. Once these contacts are vaccinated, they can return to the setting (exception, healthcare workers).
    • Contacts who are unvaccinated and without other evidence of immunity should be advised to remain at home and avoid attending activities outside the home to limit transmission in case they develop varicella.
    • High risk who received VariZIG: exclude from outbreak setting through 28 days post-exposure.
    • If the outbreak continues, exclusion of susceptible persons, including high risk contacts without evidence of immunity should continue until 21 days after rash onset of the last identified patient.
    • Catch-up vaccination
    • Everyone in the outbreak setting should be brought up to date on their 2-dose schedule (i.e., should get their first or second dose of varicella vaccine as appropriate; if first dose was administered, persons should be scheduled for the second dose as age appropriate)
    • During an outbreak, varicella vaccination should be offered even if more than five days has passed since exposure. Varicella outbreaks in some settings – such as childcare centers, schools, and institutions – can last months, particularly if varicella vaccination coverage is low. Thus, offering varicella vaccine at any time during an outbreak may provide protection to people not yet exposed and shorten the duration of the outbreak.
    • For outbreaks in preschool settings, two doses of varicella vaccine are recommended for children aged 1 to 4 years for best protection.
    • Additional considerations: Varicella is endemic in the United States and many other countries. Contact investigations on domestic or international transportation (flight, bus, etc.) to identify and notify people who may have been exposed to varicella are not conducted. Country notification for patients who were infectious while in other countries and then traveled to the United States is also not conducted for varicella.

Establish Surveillance for Additional Cases

• Concomitantly with implementing control measures (i.e., exclusion of patients, vaccination of persons without evidence of immunity) and collecting data related to the outbreak, active surveillance to identify additional cases should be established.
  • A template for a varicella outbreak line list can be found here: Varicella Outbreak Surveillance.
• Cases should be considered part of an outbreak if they occur within at least one incubation period (21 days) of the previous case.
• Outbreak surveillance should continue through two full incubation periods (42 days) after the rash onset of the last identified case to ensure that the outbreak has ended.

Communication with Providers and the Public about Varicella

• During an outbreak, effective communication to the public about varicella occurring among close contacts, an institution, or community setting is essential for varicella prevention and outbreak control.
• For those with varicella, emphasize the need to self-isolate at home.
• A person with varicella is infectious 1–2 days before rash onset. Emphasize exposed persons without evidence of immunity should stay home and avoid gatherings, especially if they have prodromal-like symptoms (e.g., fever, malaise, headache) to prevent further transmission.
• Raising provider and public awareness is important. Communication messages should include:
  • that varicella spreads easily,
  • although varicella may be perceived as a mild disease, it can cause serious complications,
  • certain groups are at high risk for serious complications, and
  • vaccination is the best prevention tool to protect against varicella.
• CDC has developed tools that public health officials and institutions can use to communicate important information to their populations during varicella outbreaks. (See Related Pages).

Definitions

• Airborne transmission, direct contact transmission, and droplet transmission: See I. Review of Scientific Data Regarding Transmission of Infectious Agents in Healthcare Settings.
• Evidence of Immunity: See above section Evidence of Immunity.
• Close contact or Exposure: Close contact with an infectious person with varicella or herpes zoster, such as close indoor contact (e.g., in the same room) or face-to-face contact. Experts differ in their opinion about the duration of contact but agree that it does not include transitory contact. Usually face-to-face contact of at least five minutes is considered significant exposure while if the exposure occurred in a large waiting room, some experts have suggested that exposure would need to be at least one hour to be considered contact. If exposure occurred in a classroom, everyone in the classroom is typically considered a contact. Localized herpes zoster is much less infectious than varicella and disseminated herpes zoster. Transmission from localized herpes zoster is more likely after close contact, such as in household settings. The definition of exposure will depend on the outbreak setting and type of interaction.
• High-risk person/contact: A person at increased risk for complications from varicella because of their age or an underlying condition (e.g., immunocompromised persons, cancer patients, pregnant women, neonates whose mothers are not immune).
• Incubation Period: 14–16 days after exposure, with a range of 10–21 days.
• Infectious Period: 1–2 days before rash onset until lesions are crusted (usually 4–7 days after rash onset) or if no vesicles, no new lesions appear within a 24-hour period.
• Varicella case: See above section Case Definition.
• Varicella outbreak: The occurrence of ≥3 varicella cases that are related in place and are epidemiologically linked.
• VZV Transmission: See above section Transmission and infectious period.

Setting specific guidance (To be used in conjunction with Outbreak Control and Investigation guidance above)

Schools

• Students and staff with varicella should be excluded from the school setting and should self-isolate at home unless medical care is needed until all lesions have crusted or, in vaccinated patients who do not develop vesicles, until no new lesions occur within a 24h period (typically 4–7 days).
• Contacts who are unvaccinated and without other evidence of immunity should be excluded from the outbreak settings from day 8 to 21 after exposure. Once these contacts are vaccinated, they can return to the school.

• Persons with herpes zoster can be potential sources for varicella outbreaks. Immunocompetent persons with herpes zoster can remain at school as long as the lesions can be completely covered. Persons with herpes zoster should be careful about personal hygiene, wash their hands after touching their lesions and also avoid close contact with others. If the lesions cannot be completely covered and close contact avoided, students and staff should be excluded from the school setting until lesions have crusted over. Persons with disseminated herpes zoster should be excluded from school until lesions have crusted over (similar to the management of patients with varicella).

Daycares/Preschools

• In outbreaks among preschool-aged children, 2-dose vaccination is recommended for optimal protection and children vaccinated with one dose should receive their second dose provided three months have elapsed since the first dose.
• Managing varicella outbreaks in daycares can pose challenges because children <12 months of age are not eligible for varicella vaccination. Exclusion of these children may not be feasible because parents would need to keep them at home until 21 days after the onset of the last varicella case in the daycare. Options to manage outbreaks in these setting may include cohorting the susceptible, exposed children together and monitoring daily for varicella-related symptoms. If a child develops fever and rash, the child should be excluded from daycare immediately until lesions crust or no new lesions appear within 24 hours. If fever is the only symptom and rash does not develop within two days of fever onset, they can return to the setting and continue daily monitoring. Children aged 6–11 months have been shown to be at higher risk of more severe varicella because maternal antibodies decline substantially by 6 months of age.39 Therefore, protecting these older infants from exposure by cohorting exposed children could help decrease risk of infection.

Residential institutions and healthcare settings

• These institutions are environments where transmission of VZV is likely to occur; residents and staff are at high risk for exposure. Risk for severe disease and complications may be higher among persons without evidence of immunity because of age or immune status.
• Varicella cases: Patients with varicella should be immediately isolated in a closed-door room (negative pressure room if available) until they are no longer infectious. Staff with varicella should be excluded from the setting and should self-isolate at home until they are no longer infectious. Airborne infection isolation (i.e., negative air-flow rooms), contact, and standard precautions should be followed for varicella, disseminated herpes zoster, or localized herpes zoster in an immunocompromised person; standard precautions should be followed for localized herpes zoster in an immunocompetent person.40 If negative air-flow rooms are not available, patients with varicella should be isolated in closed rooms with no contact with persons without evidence of immunity.
• Only staff with evidence of immunity should care for patients with varicella. Birth before 1980 is not considered evidence of immunity for health care staff.
• Screening residents and/or staff of residential and healthcare settings for evidence of immunity to varicella prior to residence or employment, and having this information readily available, will help with implementing a rapid response in the event of a varicella exposure or outbreak.
  • If serologic testing is conducted to determine persons with evidence of immunity, exposed persons who are found to be VZV IgG positive can be released from exclusion or cohorting.
• Herpes zoster cases: For immunocompetent residents or patients with localized herpes zoster, lesions should be completely covered and standard precautions should be followed. For immunocompromised persons with herpes zoster or persons with disseminated herpes zoster, the management is similar to that of patients with varicella. For healthcare personnel who develop herpes zoster, lesions should be completely covered with a taped dressing and, in addition to standard contact precautions, the healthcare worker should be removed from direct care of patients at high risk for severe complications from varicella. A healthcare worker with disseminated herpes zoster should be excluded from work until lesions have crusted over.
• For more information, see: Preventing Varicella-Zoster Virus (VZV) Transmission from Herpes Zoster in Healthcare Settings.
• Cohorting: If exposure occurs in a residential institution setting where exclusion of exposed persons without evidence of immunity is not feasible, the exposed group can be cohorted together to decrease risk of exposure to others in the setting. If cohorting is not possible, grouping with persons with documented evidence of immunity would be acceptable. These persons should be monitored closely daily during the 8–21 days postexposure for symptoms suggestive of varicella. If anyone develops symptoms, they should be immediately isolated until they are no longer infectious.
• In healthcare settings, contacts include patients sharing the same hospital room with an infectious patient or direct face-to-face contact. Exposure or contact in a healthcare setting also depends on where the exposure occurred and the type of exposure. For example, if the exposure occurred in a large waiting room, and the patient did not move then that can be taken into consideration when determining exposure; other criteria used include being in the same room for at least one hour. Additionally, consideration should be given to potential exposure due to the air flow in the facility or movement of infectious patients outside of their rooms.
• The amount of time that a room previously occupied by a patient with varicella should remain vacant to clear the air of airborne contaminants depends on the air changes per hour of the room. Table B1 "Air changes/hour (ACH) and time required for airborne-contaminant removal by efficiency" from the 2003 Guidelines for Environmental Infection Control in Health-Care Facilities helps determine the length of time a room must be vacant for air contaminant removal for infectious diseases such as tuberculosis, varicella, and measles.
• Other guidance specific for healthcare settings can be found here:
  • Guideline for Isolation Precautions
  • Preventing Transmission of Infectious Agents in Healthcare Settings
  • Infection Control in Healthcare Personnel
  • Immunization of Healthcare Personnel
• VZV is very sensitive to heat and dryness. The virus is also sensitive to standard cleaning disinfectants so those can be used to clean surfaces that were in contact with a person or respiratory tract secretions of a person with varicella.

Correctional/detention facilities

• Recommendations about cohorting, serologic testing and screening in residential settings also apply to correctional/detention facilities.
• Additional guidance can be found on the Bureau of Prison's documents: Varicella Zoster Virus Infections (2016) & Varicella Timeline Calculator (2011).

Ships/Flights

• Varicella is not internationally notifiable and contact tracing is not done if there is an exposure.
• Additional guidance for ships can be found here: Guidance for Cruise Ships on Varicella (Chickenpox) Management
• General guidance for flights: Airline Guidance

Resources

• Webcast related to this manual
• CDC Varicella disease web site
• Varicella vaccination
• CDC Varicella Website: Chickenpox (Varicella)
• Fact sheet for parents in English: Chickenpox Vaccines for Children | CDC
• Fact sheet for parents in Spanish: Vacunas contra la varicela para niños | CDC
• Infographic in English and Spanish: Chickenpox Vaccine Saves Lives Infographic | CDC
• Chickenpox Vaccine Information Statement (English | Other languages)
• Combined Measles, Mumps, Rubella and Varicella Vaccine Information Statement (English | Other languages)
• Varicella (Chickenpox) – Preventive Measures for Travelers
• Varicella Clinical Diagnosis Fact Sheet for Providers (English | Spanish)
• Varicella Breakthrough Infographic for Providers: Do You Know What Breakthrough Varicella (Chickenpox) Looks Like?