A comprehensive study published in the New England Journal of Medicine reveals that while H5N1 avian influenza remains a significant concern, U.S. cases have followed a notably different pattern than historical outbreaks, with leading health officials continuing to advocate for heightened vigilance without alarm.
Of 46 U.S. cases documented between March and October 2024, all but one were linked to occupational exposure, with most patients experiencing mild symptoms and none requiring hospitalization. The study found that 25 cases involved exposure to infected dairy cows, 20 to infected poultry, and one case had no identified exposure source.
The virus remains low risk to the general public, emphasize NIAID Director Jeanne M. Marrazzo and respiratory diseases chief Michael G. Ison in their recent commentary, though they stress the importance of careful monitoring as the virus continues to demonstrate its adaptability.
The new research reveals a distinct symptom pattern, with 93% of occupationally exposed patients developing conjunctivitis, while only 36% experienced respiratory symptoms. This profile differs significantly from historical H5N1 cases, which have shown a roughly 50% mortality rate globally since 2003.
Recent developments underscore the virus’s expanding reach. In Arizona, wastewater monitoring has detected the virus in Phoenix, Surprise, and Tempe, though local health officials maintain risk levels remain low. “Given that there is no recent documented spread of H5N1 influenza from human to human, the overall risk of avian flu to people remains low,” says Dr. Nick Staab of Maricopa County Department of Public Health.
The virus’s adaptability has become increasingly evident. In Arizona alone, December saw infections in diverse species at the Wildlife World Zoo, including a cheetah, mountain lion, and white tiger, while British Columbia reported Canada’s first presumptive human case in November.
The NEJM study identified suboptimal use of personal protective equipment among exposed workers as a key concern, with only 71% using gloves, 60% using eye protection, and 47% using face masks. This finding aligns with the NIH officials’ emphasis on improved collaboration between human and veterinary medicine sectors.
Surveillance remains particularly crucial after recent severe cases, including the first “severe” U.S. case in Louisiana requiring hospitalization. The virus mutations identified in serious cases highlight the need for rapid genomic sequencing and data sharing to track potential person-to-person transmission risk.
Current vaccine candidates show promise against circulating strains, which remain susceptible to available antivirals. The study found that 87% of cases received prompt antiviral treatment, with most patients starting treatment within two days of symptom onset.
These findings reinforce the NIH officials’ call for a balanced approach that combines enhanced monitoring with practical prevention measures, particularly as the virus affects new species and environments. The CDC notes that while most wild birds carry the virus without illness, it can be fatal for domesticated birds and has shown increasing ability to infect mammals.
The research suggests that while current U.S. cases have been predominantly mild, continued vigilance and improved protective measures for exposed workers remain essential as the virus continues to evolve and spread across species barriers.