With bird flu cases continuing to rise in the US and a teenager in Canada now in critical condition after contracting the virus, alarm bells are ringing about how big the outbreak could become.

So far in 2024, 46 people have been infected with the highly pathogenic H5 strain of bird flu, according to data from the Centers for Disease Control and Prevention (CDC). About 25 of these infections have been linked to dairy cattle, 20 to poultry, and one case in Missouri stemmed from an unknown source.

As for the teenager in Canada, who was previously described as “healthy” during a press conference on Tuesday, the source of the infection is also unknown. They had not been exposed to farms, where the virus is most common.

A recent outbreak on a pig farm in Oregon – the first of its kind in the US – raised further concerns because pigs are known to transmit diseases to humans.

According to the CDC, the risk to the general public remains low and no cases of human-to-human transmission have been reported to date.

But with every human infection, the virus has the opportunity to mutate again and spread among the population. According to experts, if there were human-to-human transmission, the consequences would be uncertain but could potentially cause a pandemic.

“Before COVID, influenza was the cause of most of the recent recorded pandemics that we know of,” Jeremy Rossman, a senior lecturer in virology at the University of Kent in Britain, told me. Newsweek.

Rossman explained that the risks of flu pandemics are therefore very high, but bird flu presents a big unknown. Because the population has not been exposed to H5 bird flu, immunity will be much lower than with other flu variants.

He added: “We just don’t know what that would look like and that’s the biggest concern.”

The need for a lockdown would depend on what form the mutation that allows bird flu to spread among humans would take.

“If we start to have human-to-human transmission, especially in the winter in the U.S. when the flu spreads best anyway, there’s a very good chance that this virus is going to spread,” Rossman said.

“Now the implications of that are not clear, because historically bird flu in humans can lead to mortality rates as high as 60 percent. But we’re not seeing that, even with the spillover cases from livestock here.”

In the U.S., human cases so far have generally been mild, the CDC said, with most infected individuals showing little more than conjunctivitis and mild flu-like respiratory symptoms.

“It’s possible that adapting to humans could restore some virulence, but it’s also possible that you could end up with H5N1 that spreads from person to person and still causes mild disease,” Rossman said.

“We just don’t know what it would be like if we did indeed get this human-transmitted bird flu.”

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