What to know
- CDC has developed strategic priorities for improving global influenza control, prevention, preparedness, and response. These priorities guide research and surveillance activities around seasonal and pandemic influenza preparedness and response.
- CDC works to address these strategic priorities through ongoing collaboration with public and animal health partners at the local, state, and national level.
- CDC has identified the following primary HPAI A(H5N1) scientific response objectives for the current outbreak of HPAI A(H5N1) in dairy cattle, other animals, and people.
Overview
Beginning the week of March 25, 2024, the U.S. Department of Agriculture confirmed detections of highly pathogenic avian influenza HPAI A(H5N1) virus infection in dairy cows in the United States. On April 4, 2024, CDC initiated a center (National Center for Immunization and Respiratory Diseases)-led emergency response for the HPAI A(H5N1) outbreak in dairy cows with a One Health approach. Since April 2024, several human cases of H5N1 have been detected in association with the ongoing outbreak of HPAI A(H5N1) in dairy cows and other animals. Human infections have occurred in dairy workers who had direct exposure to cattle presumed to be infected with HPAI A(H5N1) virus (H5N1 Bird Flu: Current Situation).
The HPAI A(H5N1) viruses currently circulating in the United States have thus far not demonstrated the ability to efficiently bind to receptors that predominate in the human upper respiratory tract. This is a major reason why CDC assesses the current risk to the public from HPAI A(H5N1) viruses to be low. However, influenza viruses have potential to rapidly evolve and HPAI A(H5N1) viruses are widely prevalent globally in wild birds. Therefore, continued comprehensive and coordinated, multisectoral surveillance across public health and animal health for these viruses in wild birds, poultry, mammals, and people worldwide, are critical to determine the public health risk.
CDC has developed strategic priorities for improving global influenza control, prevention, preparedness, and response. These priorities guide research and surveillance activities around seasonal and pandemic influenza preparedness and response. CDC works to address these strategic priorities through ongoing collaboration with public and animal health partners at the local, state, and national level. Additionally, CDC has identified the following primary HPAI A(H5N1) scientific response objectives for the current outbreak of HPAI A(H5N1) in dairy cattle, other animals, and people.
Objective 1
Prevent infection and illness in people exposed to HPAI A(H5N1) viruses.
Focus Area: Understanding the risk of infection among people exposed to infected dairy cattle, other animals, and their environment or contaminated animal products (e.g., raw milk).
Focus Area: Determining what measures most minimize the risk of infection among exposed persons. This includes personal protective equipment (PPE), and administrative and engineering controls.
Focus Area: Identifying host, pathogen, and exposure risk indicators for severe illness.
Focus Area: Monitoring and evaluating the effectiveness of influenza antiviral medications in preventing and attenuating illness, and public health interventions, including A(H5N1) vaccine (should it be employed).
Objective 2
Understand human infection and illness with HPAI A(H5N1) virus (clinical, virologic, and epidemiologic characteristics).
Focus Area: Monitoring for human infections using existing influenza surveillance platforms and developing strategies for enhanced surveillance and laboratory testing.
Focus Area: Determining how widespread human exposure and infection are. This includes estimating the prevalence and incidence of human infections.
Focus Area: Identifying the primary means of transmission for HPAI A(H5N1) human infections. This includes animal-to-human zoonotic transmission and transmission via fomites. It also includes assessment of how the virus gains entry and replicates in humans.
Focus Area: Describing the spectrum of human clinical illness, including prevalence of severe illness, illness resulting in hospitalization or death, and asymptomatic and pauci-symptomatic cases.
Focus Area: Describing parameters important to human infection and resolution of illness, including estimated incubation period and duration of infectiousness.
Focus Area: Employing animal models to help describe clinical presentation, virulence, and transmissibility of these HPAI A(H5N1) viruses compared to seasonal and other zoonotic influenza viruses.
Focus Area: Identifying virologic characteristics of HPAI A(H5N1) viruses. Identifying genetic markers associated with increased infectivity, transmissibility or reduced antiviral susceptibility. Tracking genetic changes that occur in the virus during animal and human infections.
Objective 3
Prepare for and mitigate the possibility of an HPAI A(H5N1) virus pandemic.
Focus Area: Estimating the pandemic potential of this HPAI A(H5N1) virus with the Influenza Risk Assessment Tool (IRAT).
Focus Area: Conducting comprehensive antigenic, phenotypic, genotypic, and evolutionary characterization of HPAI A(H5N1) viruses detected in humans and animals.
Focus Area: Identifying candidate vaccine viruses (CVVs) expected to provide protection against currently circulating HPAI A(H5N1) viruses in animals; evaluating antiviral drugs to assess emergence of drug resistant viruses; and developing diagnostic test methods and additional assays to rapidly and accurately identify HPAI A(H5N1) virus infections.
Focus Area: Estimating the impact of nonpharmaceutical interventions and medical counter measures, including pre-pandemic H5 vaccines and potential H5 vaccines made using existing candidate vaccine viruses in preventing infection and/or severe illness, should widespread person-to-person transmission occur.
Focus Area: Coordinating with the WHO's Global Influenza Programme and the Global Influenza Surveillance and Response System (GISRS) and the OFFLU animal health network (World Organisation for Animal Health, Food and Agriculture Organization, and reference laboratories) to support rapid information and resource sharing. As a WHO Influenza Collaborating Centre, the CDC Influenza Division actively supports global surveillance efforts and contributes materials, technical assistance, and data to global veterinary and public health partners to guide pandemic preparedness planning, including development/deployment of H5 diagnostic tests, monitoring for antiviral resistance, recommendations/development of vaccine candidates, and virus risk assessment.
Focus Area: Conducting immunologic and virologic pandemic risk assessment of novel influenza viruses in animal models and other model system.
Focus Area: Determining virus and host factors that impact virulence and transmission of novel influenza viruses, including conducting serology studies to determine the population immunity among the general population to HPAI A(H5N1) viruses.
Focus Area: Evaluating strategies to increase uptake of public health interventions such as vaccines.