Why Finland and others are vaccinating people against bird flu

WORKERS AT POULTRY and fur farms in Finland will, in the coming days, receive vaccines against bird flu. Fourteen other EU countries have signed up to procure bird-flu vaccines through a programme set up by the European Commission. America’s government has also bought vaccines in anticipation of a pandemic. And it recently commissioned Moderna, a pharmaceutical company, to create an mRNA bird-flu vaccine using a technology that was effective in protecting against covid-19. So why are countries vaccinating people against bird flu?

The illness is also called avian flu or highly pathogenic avian influenza. The usual carriers are wild waterfowl; when these birds migrate, so does the virus. It is easily transmitted to domestic poultry and is highly contagious and deadly for them. Usually it is rare for bird flu to infect mammals, including humans. But the strain of the virus that is currently circulating, H5N1, has infected hundreds of mammals. This spring it was found in dairy cows in Texas. It has since been found in dairy herds in at least 12 American states. With each mammal that is infected, there is a possibility that the virus mutates, allowing it to jump to humans more easily.

In the nearly three decades since H5N1 was first detected in geese in China, worldwide around 900 people are known to have been infected, usually from contact with infected birds. Nearly half of them died. Still, mild or asymptomatic infections would have gone undetected, making the fatality rate lower. Since the current outbreak reached Europe and the Americas in 2021, cases have been reported only in Britain (five) and the United States (also five, the latest of them in July). All of them worked on dairy or poultry farms, and their symptoms were mild (including eye infections and respiratory symptoms).

Experts are nevertheless concerned about this outbreak in mammals, and have highlighted gaps in the surveillance of H5N1. Testing of wastewater in America shows that outbreaks are going undetected. And in early May, the Food and Drug Administration found that about 20% of milk samples from store shelves across America contained H5N1 (which is killed by pasteurisation, making the milk safe to drink). Unlike domestic poultry, which show clear symptoms of infection, making their eggs or meat unlikely to reach supermarkets, cows have milder symptoms that are harder to spot. Farm workers in America who feel ill may go unnoticed if they do not get treated; and they may be unwilling to report their symptoms to avoid losing pay.

The current bird-flu vaccines were created using the same method as seasonal influenza jabs. Experts select the virus strain, in this case H5N1, that they predict will circulate in an upcoming bird-flu season, adapt the virus to grow in fertilised chicken eggs (which can take six months) and then inactivate it to distribute in flu shots. This was the technique used by CSL Seqirus, the influenza-vaccine company that created the two-dose shot to  be distributed in Finland. As well as in eggs, the virus can be grown in cells. The American government purchased 4.8m doses of cell-based vaccines from CSL Seqirus in late May. Another type of vaccine makes use of mRNA. Designing these only requires the genetic information of the virus, and can be quickly adapted to new strains. A study led by researchers at the University of Pennsylvania developed an experimental mRNA vaccine for H5N1 which showed promising results in preventing illness in mice.

At the moment experts say that the risk of H5N1 to the public is low. No cases have been detected in Finland, or elsewhere in the EU. It does not seem to be spreading easily between people. And two antiviral oral medications—oseltamivir and baloxavir marboxil—are effective against the virus. Countries are stockpiling vaccines specific to the currently circulating strain of H5N1 as a means of pandemic preparedness, in order to respond quickly if there are signs of human-to-human transmission. Finland plans to vaccinate only those workers at greatest risk in an effort to prevent the virus from evolving further. (Of those, 300 will be enrolled in a study to assess how well the vaccine protects against infection.)

More worrying is the extent to which the virus has been spreading between animals undetected. There are bird-flu vaccines for domestic poultry, but they are not widely used because they are costly, often require two doses and can limit the export of meat (many trade agreements forbid the sale of products from vaccinated animals). Developing H5N1 vaccines for cows is challenging partly because some testing must be done in labs with high levels of biosecurity—few can accommodate cattle. Even if H5N1 does not lead to a pandemic, says Meghan Davis of Johns Hopkins University, the creation of more robust vaccines and surveillance systems is a “good dress rehearsal” for the next one. ■