As the number of people — particularly agricultural workers — who have fallen ill with avian influenza (AI) has increased, the US government has already allocated $72 million to expand its vaccine stockpiles.
Amid an outbreak of avian influenza in poultry and dairy cattle, the Biden administration announced in the first fortnight of October 2024 this increase in funding for three vaccine manufacturers in order to expand the production of human vaccines, should they prove necessary.
The H5N1 virus has affected millions of wild and commercial birds across the country, and in March it made the leap to dairy cattle for the first time. As the number of affected animals grows, so does concern about transmission to humans. In the past, H5N1 has caused mortality in humans and scientists are closely monitoring it to determine whether it poses a pandemic risk. The United States government holds a stockpile of two approved H5N1 vaccines, but plans to double it with vaccines from CSL Seqirus, GSK, and Sanofi.
“We expect to have a total of just over 10 million completed doses by the end of the first quarter of 2025″, said David Boucher, Director of Infectious Disease Preparedness and Response at the Administration for Strategic Preparedness and Response, on 4 October.
Moderna, Pfizer, and GSK are also working on mRNA vaccines against avian influenza, but these must undergo human trials and receive approval from the US Food and Drug Administration before they can be used.
In 2024, 16 people in the US have been infected with avian influenza. The US Centers for Disease Control and Prevention (CDC) confirmed the two most recent cases, both in California, both agricultural workers who had contact with infected dairy cattle at two facilities in the Central Valley. Both presented mild symptoms, including eye redness, and are being treated with antiviral medications, with no respiratory symptoms or requirement for hospitalisation.
According to the CDC, the new cases do not change its risk assessment for the general public, which remains low, and the findings were not unexpected, as the greater the number of positive herds, the more workers are exposed and the higher the likelihood of human infection.
In the coming days, the CDC will conduct additional testing on the virus samples, including genetic sequencing to monitor any changes in the virus to determine whether it is developing new mutations that could make person-to-person transmission more likely. The agency states that, at present, there is no evidence that the virus can spread from person to person.
Of the 16 confirmed human cases, six have been linked to exposure to sick or infected dairy cattle, while nine involved exposure to infected poultry. The source of infection has not been determined for one case in Missouri, confirmed in September, in which the virus was detected through routine influenza surveillance, making it the first known case of human AI in the country with no known exposure to a sick or infected animal. In late August, the individual was hospitalised in Missouri due to underlying medical conditions, though presenting no respiratory symptoms and not being critically ill, but tested positive for AI as part of routine screening.
The CDC is also attempting to reconstruct the genetic sequence of the virus from the hospitalised patient’s sample, which could reveal its origin. Analysis of the virus has proved difficult, as only a small quantity of viral genetic material could be isolated from the patient’s sample.
In the absence of specific AI vaccines, health officials are encouraging poultry and dairy workers and other high-risk individuals to receive their seasonal influenza vaccination as a means of protection.