In light of the ongoing global spread of the H5N1 avian influenza, U.S. public health experts are reassured that current treatments and vaccines are effective against severe disease.
The virus, which has caused sporadic human cases, remains primarily a threat to birds and mammals, with limited transmission to humans. Health authorities emphasize the importance of balanced vigilance and maintaining standard routines while continuing to monitor and respond to the evolving situation.
H5N1 Avian Influenza Risks and Responses
The highly pathogenic H5N1 avian influenza virus (HPAI H5N1) poses a low risk to the general public, according to U.S. public health experts. They believe current treatments and vaccines, along with those under development, are adequate to prevent severe illness. Despite this, the National Institutes of Health (NIH) and its federal partners continue to closely monitor the virus and assess any changes, as emphasized by officials from the NIH’s National Institute of Allergy and Infectious Diseases (NIAID).
In a commentary published on December 30 in the New England Journal of Medicine, NIAID Director Dr. Jeanne M. Marrazzo and Dr. Michael G. Ison, Chief of the Respiratory Diseases Branch, urge the public to strike a balance between heightened awareness and maintaining normal routines when it comes to HPAI H5N1.
Global Spread and Recent Developments of H5N1
Since 1996, HPAI H5N1 influenza viruses have circulated in at least 23 countries. In late 2021, HPAI H5N1 spread from Europe to North America causing sporadic infections among wild birds and poultry farms. In 2022, the virus spread to South America where it devastated birds and marine mammals. In March 2024, USDA scientists identified HPAI H5N1 in U.S. dairy cows, and it subsequently reached herds in 16 states. The virus has been detected in dairy herds in three states over the past 30 days, according to USDA/APHIS. In 2024, the virus has caused 66 confirmed and 7 probable cases of influenza in people in the U.S. and one case in Canada. These human cases have been caused by either the H5N1 type circulating in birds (D1.1) or the type circulating in dairy cows (B3.13).
Against this backdrop, Drs. Marrazzo and Ison say there are four keys to controlling the current outbreak. The first imperative is timely, effective collaborations among investigators in human and veterinary medicine, public health, health care, and occupational workers, such as dairy and poultry workers.
Strategic Response to H5N1 Challenges
This involves cultivating trust not only between numerous entities, but with people seeking care for symptoms of concern, including conjunctivitis, the authors write. Fortunately, so far most U.S. cases of HPAI H5N1 have been mild and resolved on their own without the need for treatment.
Their second key is a focus on the Canadian HPAI H5N1 patient, who developed respiratory failure and required life-saving medical intervention and treatment before recovering. The authors write that mutations found in the virus in this patient highlight an urgent need for vigilant disease surveillance to identify and assess viral changes to evaluate the risk for person-to-person transmission. Effective surveillance, they say, requires that complete genomic sequencing data from animals and people are made rapidly and readily available.
Without information pertaining to where and when isolates were collected, the data cannot be linked phylogenetically to other reported sequences, limiting insight into how the virus is spreading, they write. These data would also provide opportunity for early detection of mutations that might portend avidity for human respiratory epithelium, which may require as little as one mutation in the virus.
Continuing Medical Innovation and Prevention Measures
Third, researchers must continue to develop and test medical countermeasures—such as vaccines and therapies that eliminate or alleviate disease—against H5N1 and other influenza viruses. Fortunately, current vaccine candidates neutralize the circulating strains, which so far are susceptible to antivirals that could mitigate transmission and severity of illness, they write.
Lastly, Drs. Marrazzo and Ison encourage people to take precautions to prevent exposure to the virus and minimize the risk of infection. For example, people who work with poultry and cows should use personal protective equipment and educate themselves about occupational risks when working with birds and mammals, as CDC and USDA have repeatedly recommended.
Ideally, following these four steps will help scientists and public health officials investigating HPAI H5N1 to answer the many remaining questions more quickly about how the virus is spreading, evolving, and affecting people, other mammals, and birds.
Reference: “The Emerging Threat of H5N1 to Human Health” by Michael G. Ison and Jeanne Marrazzo, 30 December 2024, New England Journal of Medicine.
DOI: 10.1056/NEJMe2416323
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