A horde of influenza viruses is sweeping through wild bird populations around the world. If any gain the ability to spread between humans, we may face a deadly flu pandemic.
Last week, World Health Organization (WHO) head Tedros Adhanom Ghebreyesus said that while the risk to humans is low, “we cannot assume that will remain the case and we must prepare for any change in the status quo”. So, how ready are we for such a pandemic?
Flu viruses constantly mutate. Periodically, they can cross over from animals to people, or hybrid animal-human strains emerge, and these can be more dangerous.
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Since 1997, there have been multiple deadly outbreaks in poultry farms of a subtype of the bird flu virus called H5N1, which doesn’t readily infect humans.
In birds, H5N1 has diverged into more than 30 genetic variants, which have caused a large number of deaths in wild bird populations and killed some mammals that feed on birds, although there is as yet no evidence the variants are being passed between mammals.
Animal health experts are tracking flu cases, including bird flu, among animals around the world. at the UK’s Animal and Plant Health Agency says parts of South America may need help with this. The region has seen several large outbreaks in wild birds and may be under-resourced for tracking, he says.
If bird flu does evolve to spread between people, vaccines based on that specific strain would be needed. Many new types of flu vaccine are in development, including ones made from mRNA, the basis for some of the vaccines for covid-19, which is caused by a coronavirus.
Nevertheless, the tried and tested flu vaccines already have a huge industry behind them and would be the mainstay of the vaccine response, says Wenqing Zhang at the WHO.
Manufacturers such as GlaxoSmithKline and Sanofi already change the flu strains in their seasonal vaccines each year, depending on what has recently been circulating. It takes only about four months from selecting the strains to producing a vaccine.
The WHO has sent samples of some H5N1 viruses to vaccine manufacturers, but mass production can’t begin because we don’t know which of its genetic variants may cause a pandemic, says Zhang. It might not even be one of the 30 variants that are circulating, but one with further changes that hasn’t yet emerged.
“For a vaccine to be effective, you need to make sure that the viruses contained in the vaccines match well those viruses causing infections,” says Zhang.
Unlike at the start of the covid-19 pandemic, some antiviral drugs are available that can be given to people with severe flu, such as oseltamivir. The WHO is in talks with manufacturers about donating such medicines to low and middle-income countries if a bird flu pandemic were to start.
But we must “cross our fingers” that any pandemic bird flu virus would be susceptible to these antivirals, as new pathogens can evolve resistance, says Zhang.
Lateral flow tests, also known as rapid antigen tests, proved useful during coronavirus surges to let people know if they should isolate. These are available for flu viruses that infect people and could be scaled up for bird flu.
Overall, Zhang says that if a bird flu pandemic begins, the world would be more prepared than it was before covid-19. “Lessons learned and experience gained from covid-19 are valuable for preparing for future pandemics,” she says.
