U.S. Public Health Preparedness and Response to Avian Influenza A(H5N1) Viruses

Courtesy of NIAID

Since 2020-2021, highly pathogenic avian influenza (HPAI) A(H5N1) clade viruses have spread among wild birds worldwide, causing poultry outbreaks and spillover to terrestrial and marine mammals. HPAI A(H5N1) clade viruses were first identified in wild birds in North America in late 2021 and continue to evolve and spread. Since February 2022, in the U.S., HPAI A(H5N1) viruses were detected in wild birds in 49 states, in terrestrial and marine mammals in 27 states, in livestock in a small number of states, and caused outbreaks in commercial poultry or backyard bird flocks in 48 states.

Sporadic human HPAI A(H5N1) virus infections with more than 50% cumulative case-fatality proportion, primarily associated with exposures to sick or dead infected poultry, have been reported in 23 countries. One case of HPAI A(H5N1) was reported in a person who reported fatigue while culling infected poultry in Colorado in April 2022. Although the number of reported human cases of HPAI A(H5N1) worldwide has been small since 2022,5 because HPAI A(H5N1) viruses continue to spread among birds and other animals, the potential for human infections remains. As HPAI A(H5N1) viruses pose pandemic potential, Kojima, et al. (2024) assessed components of public health preparedness and response in the U.S.

In collaboration with the Council of State and Territorial Epidemiologists, the Centers for Disease Control and Prevention (CDC) surveyed State and Territorial Epidemiologists in 55 jurisdictions on public health practices for A(H5N1) virus identification, monitoring of human exposures to infected animals, and recommendations for use of influenza antivirals and potential vaccines. The online survey was conducted from January 10 through March 6, 2024, before HPAI A(H5N1) virus infections were identified among dairy cattle in multiple states4 and a human case of HPAI A(H5N1)–associated conjunctivitis in a dairy farm worker was reported in Texas. Responses were analyzed using descriptive statistics.

Responses were received from all 55 state and territorial jurisdictions surveyed. Since January 2022, persons exposed to A(H5N1) virus–infected animals and monitored for symptoms were reported in 50 (91%) jurisdictions. Of these 50 jurisdictions, human exposures to A(H5N1) virus–infected animals were reported in backyard flocks in 44 (88%), commercial poultry in 41 (82%), wild birds in 27 (54%), and sick or dead mammals in 9 (18%). Among 49 jurisdictions that reported having A(H5) virus testing capacity, 29 (59%) reported testing respiratory specimens from symptomatic persons since January 2022. In 33 of 50 jurisdictions (66%), public health authorities reported difficulties in monitoring A(H5N1) virus–exposed persons due to personnel shortages or lack of funding. Among 50 respondents, 19 (38%) public health authorities reported recommending empirical antiviral treatment before performing influenza testing for persons being monitored after A(H5N1) virus exposure who develop symptoms. Eighteen of 55 jurisdictions (33%) would recommend post-exposure antiviral prophylaxis for close contacts of any person with laboratory-confirmed A(H5N1).

If an influenza A(H5N1) vaccine was available for first responders, public health authorities in 37 (67%) jurisdictions would offer vaccination now for veterinary personnel responding to A(H5N1) virus–infected animals and for public health personnel investigating A(H5N1) virus–exposed persons in 20 (36%) jurisdictions. In 34 (62%) jurisdictions, including 32 of 50 states (64%), public health authorities reported maintaining antiviral stockpiles for pandemic influenza.

Reference: Kojima N, et al. US Public Health Preparedness and Response to Highly Pathogenic Avian Influenza A(H5N1) Viruses. JAMA. Published online May 21, 2024. doi:10.1001/jama.2024.10116