Why scientists are worried about bird flu

Why Scientists are Alarmed by the Growing Threat of Avian Influenza

a hen. Illustrated | Getty Images

The 2022-2023 bird flu outbreak is officially the worst on record. Since last winter, around 208 million birds have died or been culled from H5N1 worldwide, driving up egg and chicken prices worldwide. In recent days, scientists have expressed increasing concern that a mutation could cause a “spillover” event, in which H5N1 is transmitted more efficiently from person to person.

Why are scientists concerned?

Revelations about the spread of bird flu at a Spanish mink farm in October have raised alarm. The mink were infected with an H5N1 variant called 2.3.4.4b, which was discovered in 2020 and has since made its way around the world. While it’s not uncommon for mammals to contract bird flu after direct contact with infected birds, the mink farm showed evidence of transmission between the mink themselves, “unprecedented in mammals,” wrote Columbia University professor Zeynep Tufekci The New York Times.

Samples obtained from the mink showed a mutation that made it easier for the virus to gain a foothold in mammals, and this appears to be the first case of such transmission outside of laboratory settings. What the virus can do to mink, it can do to us. That said virologist Tom Peacock from Imperial College London Science this “is a clear mechanism for the onset of an H5 pandemic.” Dutch virologist Marion Koopmans said on Twitter that “we are playing with fire”. The more animal species are infected with H5N1, the more opportunities the virus has to enter humans via an intermediate host. The incident at a mink farm is one of 119 outbreaks in animals since October 2021, according to the BBC. During that period there have been five confirmed human cases and one death.

How deadly is H5N1 to humans?

World Health Organization data shows that over the past 20 years there have been 868 documented human H5N1 infections who contracted the virus through direct contact with the saliva, mucus and droppings of infected birds. Of these cases, 457 resulted in deaths, giving H5N1 a known case fatality rate (CFR) of over 53 percent. While the infection fatality rate (IFR), an estimate that accounts for asymptomatic or mild cases that go unreported, may not be as high, there is no question that if the virus could spread easily between people, it would cause a grave crisis of public health. In 2008, a group of Canadian researchers estimated that the human CFR of a mutant avian influenza pandemic would range from 14 percent to 33 percent, making the COVID-19 crisis tiny in comparison. Other researchers are more optimistic, believing that the mortality rate of the existing strain, which infects humans through direct contact with birds, is much lower than WHO estimates due to missed cases.

Why was this outbreak so bad?

The 2022-2023 disaster is ongoing and nearing the one-year mark, and scientists don’t have a clear answer as to why this outbreak is so much worse than those in the past.

Avian flu kills nearly all the birds it infects and can burn through entire flocks in a matter of days. At least 80 bird species have been infected during this outbreak, which has affected countries around the world. Health authorities have taken different approaches to combating the outbreak. China is vaccinating commercial birds, while French and British authorities have encouraged farmers to bring their flocks indoors to avoid infection from passing wild birds. U.S. farmers are being encouraged to implement a range of biosecurity measures, including limiting the number of people entering and exiting farm facilities and placing “disinfecting footbaths” at entrances to stalls. Other producers have effectively gone into lockdown to limit their own outreach.

Other countries, including France and the Netherlands, are experimenting with new vaccines in what has so far been a last resort. Vaccinated birds and their eggs are difficult to export commercially – paradoxically because vaccination is taken as evidence that avian influenza is rampant in the exporting country and because vaccinated birds may not show any symptoms if infected. But the most common approach, and the one used in the United States, is to cull domesticated herds, which can be excruciating and financially ruinous for farmers.

How concerned should we be?

Experts have been warning of the occurrence of a pandemic-capable bird flu in humans for years. No mutations that would facilitate transmission between humans have been found in humans infected with the virus, and the risk to humans not in direct contact with infected birds is negligible. In the past, there have been cases where people have been shown to be infected with versions of H5N1 that carry mutations of concern, but still did not result in a pandemic. “But it seems foolish to rely on it,” Tufekci wrote. After all, “deadly influenza pandemics have occurred regularly throughout human history.”

Efforts to develop human vaccines are ongoing. There are already existing vaccines that would likely help, but production would need to be increased dramatically and adaptations made to accommodate the new strain of flu. Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at Sheba Medical Center in Israel, said last year: “I don’t think anyone should panic about this because avian flu has existed in various places for a long time and has not yet existed at one pandemic, highly pathogenic influenza.”