While the US declared its intention to leave the World Health Organization (WHO) on 20 January, the process of severing ties with the international public health body formally takes one year. Yet US health agencies have already retreated from nearly all coordinated global health efforts around influenza surveillance. The move could jeopardise the efficacy of the next batch of flu vaccines both for the US and the rest of the world.
This comes as the US is in the midst of its most severe flu season in 15 years. At least in the country have caught the illness since October and roughly 16,000 have died from it – and the season is only half over.
Numerous factors are probably behind the surge, including lower vaccination rates, says at Johns Hopkins University in Maryland. While adult flu vaccination rates are nearly the same as they were this time last year – about of US adults have had the shot as of 8 February – childhood vaccination rates have dipped. In early February 2024, nearly 51 per cent of adolescents were inoculated against seasonal influenza. Now, only 46 per cent are.
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The efficacy of this season’s flu shot may also be to blame, though it is too early to say for certain. The two predominant influenza strains circulating in the US are the same ones that dominated the southern hemisphere’s flu season, which ran from April to September 2024. Data from five South American countries suggests the flu vaccine reduced people’s risk of hospitalisation for influenza by about , which is on the lower end of the typical efficacy range. If a similar rate is seen in the northern hemisphere, it suggests this year’s flu shot was a weak match.
All of this underscores the importance of an upcoming WHO meeting. Scheduled for , the meeting will bring together influenza experts from around the world to select which strains the next flu shot will target. This decision is based on influenza samples collected from . The samples will then be further analysed at WHO collaborating centres – located in the – to characterise how the virus spreads, evolves and interacts with vaccines and other treatments.
These seven collaborating centres, two of which are based in the US, play a major role in global influenza surveillance and response preparedness, says at the WHO. The trouble is, the US centres stopped communicating with the WHO on 24 January, mere days after US president Donald Trump took office and ordered the withdrawal from the WHO. “We are communicating with them, but we haven’t heard anything back,” says Van Kerkhove.
This means the US has stopped sharing influenza data with the WHO and participating in crucial meetings on influenza preparedness. It is also highly unlikely that US representatives will partake in the upcoming meeting to determine the composition of next season’s flu shot – a massive loss given the US Centers for Disease Control and Prevention (CDC) is the largest global resource for the control of pandemic and seasonal influenza, says Sorrell.
The WHO is currently working with other collaborating centres to fill the information gap left by the US, says Van Kerkhove. The halt in US communication shouldn’t impact the WHO’s ability to develop an effective flu vaccine for next season, she says. But it will certainly make it more challenging to do so in the future.
It will also have ramifications for US public health. “We don’t get to provide our input on strains that we are most concerned about in the US and discuss mutations that we are observing here. Our technical experts, who are some of the best in the world, are not able to contribute to that conversation,” says Sorrell. “So, we are not only putting the world at a disadvantage, but absolutely the average American who would be looking to be vaccinated next year against seasonal flu.”
It is unclear whether the US will have any input on the development of influenza shots moving forward. The CDC didn’t respond to a request for comment. A spokesperson for Sanofi – the largest flu vaccine manufacturer in the world – said it will continue to play a role in providing influenza protection both inside and outside the US, and that it “will be ready to support final strain selections in time for the season”. They declined to answer whether final strain selection will take place with individual countries, such as the US, in addition to the WHO.
“We have no guarantees about what the next flu season will be like,” says Sorrell. “We’re essentially putting blinders on to be able to respond effectively.”
Will bird flu affect vaccine production?
A bird flu virus, known as H5N1, is decimating global poultry flocks. In the US alone, more than birds in commercial and backyard flocks have been killed because of the virus so far this year. As a result, egg prices in the US rose more than in January.
Given that the majority of influenza vaccines are made using chicken eggs – necessitating millions of fertilised chicken eggs each year – this has raised concerns about whether bird flu will impact vaccine production.
But a spokesperson for Sanofi, the world’s largest flu vaccine manufacturer, says it uses pharmaceutical grade eggs. “Our biosecurity protocols are designed to prevent pathogens from entering sites where eggs and egg-based vaccines are made”, which should protect flocks from H5N1, they say.
