What is the chance of a human avian flu pandemic? – 02/27/2023 – Balance and Health

The worst-ever avian flu outbreak has made the disease endemic in some birds, inflicted huge costs on the poultry industry, spread to wild and captive mammals and, in some rare cases, infected humans.

The World Organization for Animal Health (WOAH) said this month that an increasing number of cases have been reported in mammals, “causing morbidity and mortality” in species such as otters and seals. Reports of infections in farmed mink in Spain have raised concerns, WOAH said, because cases involving large numbers of animals kept in close proximity to each other exacerbated the risk of wider transmission.

If the H5N1 virus, the main strain responsible for the last outbreak at the end of 2021, develops mutations that facilitate its transmission to humans, experts fear the emergence of a pandemic that poses more risks to global health than the Covid-19 outbreak. Although bird flu has infected relatively few humans, its fatality rate is around 50%, according to the European Center for Disease Prevention and Control (ECDC).

H5N1 is “a huge concern,” said Jeremy Farrar, an influenza expert and director of the Wellcome Trust. “You would hate to look back in the middle of an H5N1 pandemic and say, ‘Wait, we didn’t see this bird population die all over the world, we started to see mammals die, and what did we do about it?'” he said in a press conference in London this week.

According to him, more vigorous action is needed to increase stocks of vaccines for H5N1 and prevent the circulation of the virus among mammals. “If there was an outbreak tomorrow of H5N1 in humans, we would not be able to vaccinate the world in 2023,” added Farrar, who will become chief scientist at the World Health Organization in May.

What is the likelihood of a human H5N1 pandemic?

Infectious disease experts say the risk remains largely contained to the animal population — 50 million birds, including beef, have been killed by the virus or culled in this outbreak, according to the ECDC. Large-scale culling has been carried out in dozens of countries, including Japan, France and the United States.

The WHO said this month that bird flu “is still an avian virus” and that the threat, including human-to-human transmission, “is low”.

Avian flu is a “recurring problem” characterized by sporadic seasonal outbreaks, according to Gregorio Torres, head of science department at WOAH. But many countries with outbreaks reported cases throughout the year, he said. “The seasonality that [costumávamos] watching no longer exists.”

Changes in poultry farming methods and rising global temperatures that force wild birds to alter their migration patterns, as well as increased movement of animals and humans between countries, are behind the rise in cases, he said.

“The virus can be transmitted through contaminated feed, contaminated food and also contaminated trucks”, added Torres.

A crucial factor is how H5N1 evolves, which scientists say can happen in two ways: through a linear series of mutations that make the virus more efficient at spreading through a given animal species; or by recombination, when two different strains of the virus affect host cells at the same time and exchange genes, leading to greater evolutionary leaps.

“No one can predict when or where [uma mutação] it’s going to happen,” said David Heymann, professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine. “The important thing is that you keep an eye out for infections.”

What is being done to contain the spread?

Experts agree that surveillance measures in place have been adequate to identify and isolate disease, despite the enormous cost to food producers and other groups.

Torres said the focus must continue on “biosecurity”, that is, actively looking for sick animals to isolate them from healthy ones.

“It’s definitely the most effective tool to prevent animals from becoming infected,” Torres said. He added that the risk to humans, while still low overall, “has probably never been higher.”

He warned that the public should be careful when dealing with dead birds in the wild, one of the common routes of transmission to humans. In London and many other cities, city councils have warned against feeding birds in parks.

And what other measures should be taken?

Richard Ebright, professor of chemistry and chemical biology at Rutgers University, said it was “clear” that further steps should be taken to reduce the zoonotic potential of H5N1.

He called for an end to two activities that could allow avian flu viruses to jump to humans — fur farming and gain-of-function research, in which pathogens are manipulated to help scientists understand how they behave.

“The first, in effect, selectively breeds new H5N1 influenza viruses that can be efficiently transmitted in mammals,” said Ebright. “The latter, by definition, deliberately create new H5N1 influenza viruses reasonably anticipated for efficient transmission in mammals.”

“Both are unnatural. Neither offer benefits that outweigh the risks,” he added.

What countermeasures are available?

According to the WHO, vaccines for use in humans against H5N1 infection have been developed, but have not been widely used.

“Several manufacturers have developed prototype H5 vaccines that can be licensed when and if a pandemic strain of H5N1 emerges,” he said, adding that the most important tool is identifying positive cases and monitoring their contacts as part of routine outbreak investigations. . Influenza antivirals are also available.

Only a few countries, such as Russia, China and Egypt, have vaccinated animals against bird flu in the past three years, according to WOAH. But vaccines are unable to provide complete immunity or protection against disease, and many experts say the safest course of action is to separate sick animals from healthy ones.

To protect humans in the long term, Farrar advocates forming a global vaccine pipeline “for every strain of influenza that exists in the animal kingdom until at least phase 1 and phase 2 studies [em humanos]so that vaccines are known to be safe and immunogenic, and that it is possible to manufacture them well”.

^{Translated by Luiz Roberto M. Gonçalves}