Influenza Vaccination Coverage Among Adults — National Health Interview Survey, United States, 2008–09 Influenza Season

Walter W. Williams, MD

Peng-Jun Lu, MD, PhD

Megan C. Lindley MPH

Erin D. Kennedy DVM

James A. Singleton, PhD

Immunization Services Division, National Center for Immunization and Respiratory Diseases

Corresponding author: Walter W. Williams, MD, Immunization Services Division, CDC, 1600 Clifton Rd, NE, MS A-19, Atlanta, GA 30333. Telephone: 404-718-8734; Fax: 404-235-1751; E-mail: www1@cdc.gov.

Introduction

In the United States, annual influenza epidemics typically occur during the late fall through early spring. During these epidemics, rates of serious illness and death are highest among adults aged ≥65 years, children aged <2 years, and persons of any age who have medical conditions that increase their risk for complications from influenza (1–4). Adults aged 50–64 years who have underlying medical conditions have a substantially increased risk for hospitalization during the influenza season (5). Influenza illness among healthy adults aged 18–64 years typically is not as severe as the illness among adults aged ≥65 years, pregnant women, or persons with chronic medical conditions and less frequently results in hospitalization. However, influenza among healthy adults aged 18–49 years is an important cause of outpatient medical visits and worker absenteeism. An economic analysis estimated an annual average of approximately 5 million illnesses, 2.4 million outpatient visits, 32,000 hospitalizations, and 680 deaths from influenza among adults aged 18–49 years who did not have a medical condition that increased their risk for influenza complications (6). In this analysis, adults aged 18–49 years accounted for 10% of the total economic cost from influenza, or approximately $8.7 billion (6).

The most effective strategy for preventing influenza is annual influenza vaccination. Routine influenza vaccination has been recommended since the 2010–11 influenza season for all persons aged ≥6 months (4). Before this recommendation, the only group that was not recommended for routine vaccination was healthy nonpregnant adults aged 18–49 years who did not have an occupational risk for influenza exposure and who were not close contacts of persons at higher risk for influenza-related complications. According to the Patient Protection and Affordable Care Act of 2010 as amended by the Healthcare and Education Reconciliation Act of 2010 (referred to collectively as the Affordable Care Act [ACA]), as of January 1, 2014, all newly qualified health plans operating in the exchanges* must provide coverage without cost sharing for all persons, including those aged 18–64 years, for vaccinations recommended by the Advisory Committee on Immunization Practices (ACIP) (7). Influenza vaccination for adults aged ≥65 years has been a covered benefit for many years under Medicare (4). Adults aged ≥65 years have had higher influenza vaccination coverage (>62%) than persons in all other age groups (4). This report examines factors associated with influenza vaccination during the 2008–09 influenza season and suggests ways that the provisions of the Affordable Care Act might improve access to vaccination and influenza vaccination coverage. The information in this report is intended for all persons involved in annual influenza vaccination, as well as those for whom annual influenza vaccination is recommended. The results can serve as a baseline to monitor the progress and impact of clinical preventive services.

Methods

To estimate seasonal influenza vaccination coverage among adults aged 18–64 years during the 2008–09 influenza season, CDC analyzed data from the 2009 National Health Interview Survey (NHIS). NHIS collects information about the health and health care of the noninstitutionalized, civilian population in the United States and is designed to produce nationally representative samples. The NHIS questionnaire includes a set of basic health and demographic questions and questions on access to health care and use. Interviews are conducted in respondents' homes continuously throughout the year by interviewers of the U.S. Census Bureau for CDC.

To ascertain coverage estimates, participants were asked the following questions: 1) "During the past 12 months, have you had a flu shot?" and 2) "During what year and month did you receive your flu vaccine?" To ascertain coverage among persons with higher risk for complications from influenza, respondents were asked whether they had ever been told by a physician or other health professional that they have diabetes, emphysema, cancer or a malignancy of any kind (excluding nonmelanoma skin cancer), lymphoma, leukemia, or blood cancer or had coronary heart disease, angina, a heart attack, or another heart condition. Respondents also were asked whether, in the past 12 months, they had experienced an asthma episode or attack or had been told by a physician they have chronic bronchitis or weak or failing kidneys. Covariates were selected to measure associations among influenza vaccination and selected demographic and health-care access characteristics: age group, sex, race and ethnicity, marital status, educational level, employment status, poverty level, health insurance status, primary provider status, physician contacts in the previous year, hospitalization within the past year, having certain high-risk conditions, and current employment as health-care personnel.

Poverty status was defined using 2009 poverty thresholds published by the U.S. Census Bureau; below poverty was defined as a total family income of <$21,756 for a family of four (available at http://www.census.gov/hhes/www/poverty/data/threshld/thresh09.html). Respondents were classified as health-care personnel if they were currently employed in a health-care occupation or in a health-care industry setting, based on standard occupation and industry categories recoded into categories by CDC. Respondents were classified as having a regular physician if they answered affirmatively to the question, "Is there a place that you usually go to when you are sick or need advice about your health?" Although female respondents were asked whether they were pregnant at the time of the interview, estimates of influenza vaccination among pregnant women are not presented because they might be misleading. Women who became pregnant at other times during the influenza vaccination period would not be counted in the analysis, and information on the stage of pregnancy or estimated date of delivery was not available.

Kaplan-Meier survival analysis was used to determine the cumulative influenza vaccination coverage during August 2008–May 2009 using monthly interview data collected during September 2008–June 2009. Data weighting procedures are described in more detail elsewhere (8). Point estimates and estimates of corresponding variances for this analysis were calculated using statistical software to account for the complex sampling design of NHIS. Chi-square tests were used to examine significance between age groups, and t-tests were used to determine significance within strata with multiple levels. Statistical significance was defined as p<0.05.

Results

A total of 11,963 adults aged 18–64 years were included in the analysis. An estimated 70.1% were aged 18–49 years, and 29.9% were aged 50–64 years (Table 1). Most respondents (72.1%) indicated that they were employed; 13.4% of respondents had incomes below the poverty level. Most respondents (67.2%) had private insurance; however, 20.3% of respondents aged 18–64 years reported having no insurance, including 23.6% of those aged 18–49 years. A total of 81.4% of respondents reported having a regular physician, and 79.2% had at least one or more physician contacts within the past year. Among adults aged 18–64 years, 20.2% reported having a high-risk condition. Health-care personnel comprised 8.8% of respondents.

Influenza vaccination coverage overall during the 2008–09 influenza season for adults aged 18–64 years was 28.2% (Table 2). Coverage was significantly higher among adults aged 50–64 years than among those aged 18–49 years, both overall and by most demographic and health-care access characteristics examined. Influenza vaccination coverage for Hispanic adults aged 18–49 and 50–64 years was significantly lower than coverage among non-Hispanic whites in those age groups. Influenza vaccination coverage among non-Hispanic blacks and non-Hispanic whites aged 18–49 and 50–64 years was similar. Respondents aged 18–49 years and 50–64 years who were at or above the poverty level had higher influenza vaccination coverage (23.6% and 42.8%, respectively) than those who were below poverty (16.7% and 34.9%, respectively). In both age groups (18–49 and 50–64 years), influenza vaccination coverage was higher among adults with high-risk conditions (31.9% and 51.2%, respectively) compared with those without identified high-risk conditions (20.8% and 37.2%, respectively). Respondents with diabetes had higher influenza vaccination levels (49.0%) than those with heart disease (42.5%) or asthma (38.7%). Overall, influenza vaccination coverage among adults with high-risk conditions was 41.4%. Respondents who were health-care personnel had significantly higher influenza vaccination coverage (53.0%) than those who were not health-care personnel (25.8%). Women aged 18–49 years and 50–64 years had statistically higher influenza vaccination coverage than men in the same age groups (26.7% vs. 18.0% and 44.2% vs. 39.3%, respectively).

Influenza vaccination coverage was substantially higher among younger (18–49 years) and older (50–64 years) adults who had health insurance (whether private or public) than adults who did not have insurance (Table 2). However, influenza vaccination coverage was higher among adults aged 18–49 years who had private insurance than among those aged 18–49 years who had public insurance. Those who had some type of health insurance were more likely to have a regular physician and to have had two or more provider contacts within the past year than those who did not have insurance (Table 3). Coverage was twofold to threefold higher among those who had a regular physician compared with those who did not (Tables 2 and 3). In addition, influenza vaccination coverage was higher among persons who had any physician contacts within the past year compared with those who had none, with coverage increasing with increasing number of physician contacts (Tables 2 and 3). However, most respondents (56.7%–77.6%) with one or more provider contacts were not vaccinated (Table 2).

Discussion

The most effective strategy for preventing influenza is annual influenza vaccination (4). The Healthy People 2020 immunization and infectious diseases objective 12 (objective IID-12) is to increase the percentage of children and adults who are vaccinated annually against seasonal influenza (9). The Healthy People 2020 objectives for influenza vaccination range from 80% to 90% for population groups including noninstitutionalized healthy adults aged 18–64 years and adults with high-risk conditions aged 18–64 years, health-care personnel, and pregnant women. The findings reported here indicate that influenza vaccination coverage is well below the Healthy People 2020 objectives (9). Substantial improvement in influenza vaccination coverage is needed to achieve Healthy People 2020 targets.

Although the influenza vaccination level of 41.4% for noninstitutionalized adults aged 18–64 years with high-risk conditions was higher than that for adults without high-risk conditions (24.8%), the percentage is well below the Healthy People 2020 target of 90%. Vaccination of healthy adults aged <65 years can decrease work absenteeism and use of health-care resources, including use of antibiotics, when the vaccine and circulating viruses are well matched (10–12). Vaccine effectiveness among adults aged <65 years with high-risk conditions is typically lower than that reported for healthy adults; however, substantial data exist regarding the benefits of influenza vaccination in persons with high-risk conditions (4,13). The higher influenza vaccination coverage among persons with diabetes might reflect interventions to improve vaccination in this population, including support by professional organizations incorporating influenza vaccination recommendations into clinical care guidelines (4,13,14).

The findings in this report are consistent with previous reports indicating that persons who have insurance coverage, a usual place for health care or medical home, and who seek medical care one or more times during the year are more likely to be vaccinated against influenza and receive other preventive services, compared with those who are uninsured and do not have a usual place for health care (15–19). As indicated in this report and NHIS data for the 2005–06 influenza season (15), the likelihood of receiving an influenza vaccination increased with increasing numbers of health-care visits. However, many opportunities for vaccination likely are being missed; even among persons with health insurance and >10 physician contacts within the past year, approximately 57% were not vaccinated. Persons without insurance were less likely to receive influenza vaccination than their counterparts who had either private or public insurance. Uninsured persons who obtain insurance might not be able to rapidly catch up with their already-insured peers in regard to use of preventive services. Although insurance provides access to care, a relatively long period might elapse before appropriate prevention services are received (18). However, receipt of preventive services, including influenza vaccination, can increase substantially among adults who have insurance and a usual place for health care (19).

The lower seasonal influenza vaccination coverage for Hispanics and blacks compared with whites has been observed in previous influenza seasons among adults (20–22). Numerous factors play a role in these racial/ethnic disparities, including differences in attitudes toward vaccination and preventive care, propensity to seek and accept vaccination, variations in likelihood that providers recommend vaccination, and differences in quality of care received by racial/ethnic populations (4,23–32). Broad use of interventions to remove barriers to access to care and to make vaccination services in health-care and other settings a routine practice are important components of efforts to reduce these disparities (33,34).

Pregnant women have an increased risk for complications from influenza (35–42) and are a priority group for vaccination (4). Estimates for women who might have been pregnant during the 2008–09 influenza season are not included in this report because the estimates might be misleading. Pregnant women identified by NHIS were those who were pregnant at the time of the survey, and information on the stage of pregnancy or estimated date of delivery was not available. Some women who were pregnant during the vaccination period might have been missed, and some who were not pregnant during the vaccination period might have been included. A more accurate estimate of the influenza vaccination status among pregnant women can be derived by ascertaining pregnancy status during the influenza vaccination period. Starting with the 2012 NHIS, this survey will collect information on influenza vaccination before, during, or after a recent or current pregnancy to ascertain whether a woman was pregnant during the influenza vaccination period. Other data sources that more specifically ascertain which women were pregnant during the influenza vaccination period are available (43–45).

ACIP recommends that all health-care personnel be vaccinated for influenza and certain other vaccine-preventable diseases to safeguard the health of personnel and protect patients from influenza virus infection through exposure to workers with influenza (4,46). Persons who should be vaccinated include all persons working in health-care settings, who have the potential for exposure to patients or residents or to infectious materials, including body substances, contaminated medical supplies and equipment, environmental surfaces, or contaminated air. Despite annual influenza vaccination being recommended by ACIP and being one of the standards for adult immunization practice (47), influenza vaccination coverage among health-care personnel is not optimal. The rate found in this report (53.0%) is well below the 90% Healthy People 2020 target. With moderate effort, organized campaigns can attain higher vaccination levels among health-care personnel, and mandatory influenza vaccination policies for health-care personnel have been demonstrated to be a highly effective approach to achieving high vaccination coverage in this population (4).

The findings in this report are subject to at least two limitations. First, the determination of vaccination status and identification of high-risk conditions in NHIS were not validated by medical records; self-report of vaccination can introduce recall bias and might result in an overestimation of rates. However, adult self-reported influenza vaccination status has been shown to be sensitive and specific (48–50). Second, information was not available for certain high-risk conditions (such as chronic neurologic conditions) identified by ACIP.

Conclusion

Substantial improvement in annual influenza vaccination of recommended groups is needed to reduce the health impact of influenza. Successful influenza vaccination programs combine education of potential vaccine recipients and publicity, increased access to influenza vaccination in medical and complementary settings such as workplaces and commercial establishments (e.g., pharmacies and chain stores), and use of practices shown to improve vaccination coverage, including reminder and recall systems, efforts to remove administrative and financial barriers to vaccination, use of standing orders programs for influenza vaccination, and assessment of practice-level vaccination rates with feedback to staff (4). The Affordable Care Act requires that certain clinical preventive services be provided without cost sharing in Medicare and by newly qualified health plans. The Affordable Care Act also encourages state Medicaid programs to offer selected clinical preventive services with no cost sharing (7). Beginning in 2013, state Medicaid programs that eliminate cost sharing for these preventive services may receive enhanced federal matching funds for them (7,51). The expanded enrollment in public and private insurance programs expected from provisions of the Affordable Care Act might improve access to health-care services, including vaccination, for persons who were previously uninsured. Although health insurance coverage can improve access to health-care services, insurance alone might not be sufficient to achieve optimal influenza vaccination levels (or coverage). The findings in this report indicate that even among those with health insurance and >10 contacts with physicians within the past year, influenza vaccination coverage did not meet the Healthy People 2020 target. Other provisions of the Affordable Care Act that create incentives for primary care, including increased payments for primary care services provided by primary care doctors and coverage without cost sharing (34) for vaccines recommended by ACIP, also should help to improve influenza vaccination coverage.

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