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Five years on from the start of the covid pandemic, are we ready for a potential avian influenza outbreak?

This week marks a strange anniversary-it's five years since most of us first heard about a virus causing a mysterious "pneumonia." A virus that we later learned could cause a disease called covid-19. A virus that swept the globe and has since been reported to have been responsible for -and counting.

Human cases in the US are on the rise and the virus is turning up in cows and dairy products. Luckily, we have some vaccines ready to go if needed.

I first covered the virus in an article published on January 7, 2020, which had the headline "." For that article, and many others that followed it, I spoke to people who were experts on viruses, infectious disease, and epidemiology. Frequently, their answers to my questions about the virus, how it might spread, and the risks of a pandemic were the same: "We don't know."

We are facing the same uncertainty now with H5N1, the virus commonly known as bird flu. This virus has been decimating bird populations for years, and now a variant is . We know it can cause severe disease in animals, and we know it can pass from animals to people who are in close contact with them. As of this Monday this week, we also know that it can cause severe disease in people-.

Scientists are increasingly concerned about a potential bird flu pandemic. The question is, given all the enduring uncertainty around the virus, what should we be doing now to prepare for the possibility? Can stockpiled vaccines save us? And, importantly, have we learned any lessons from a covid pandemic that still hasn't entirely fizzled out?

Part of the challenge here is that it is impossible to predict how H5N1 will evolve.

A variant of the virus caused disease in people in 1997, when there was a small but deadly outbreak in Hong Kong. Eighteen people had confirmed diagnoses, and six of them died. Since then, there have been sporadic cases around the world-but no large outbreaks.

As far as H5N1 is concerned, we've been relatively lucky, says Ali Khan, dean of the college of public health at the University of Nebraska. "Influenza presents the greatest infectious-disease pandemic threat to humans, period," says Khan. The was caused by a type of influenza virus called H1N1 that appears to have jumped from birds to people. It is thought to have infected a third of the world's population, and to have been responsible for around 50 million deaths.

Another H1N1 virus was responsible for the 2009 "swine flu" pandemic. That virus hit younger people hardest, as they were less likely to have been exposed to similar variants and thus had much less immunity. It was responsible for somewhere between that year.

Avian flu in dairy cows could stick around on US farms forever, and is raising the risk of outbreaks in mammals-including humans-around the world.

To cause a pandemic, the H5N1 variants currently circulating in birds and dairy cattle in the US would need to undergo genetic changes that allow them to spread more easily from animals to people, spread more easily between people, and become more deadly in people. Unfortunately, we know from experience that viruses need only a few such changes to become more easily transmissible.

And with each and every infection, the risk that a virus will acquire these dangerous genetic changes increases. Once a virus infects a host, it can evolve and , whether it's a bird, a pig, a cow, or a person. "It's a big gambling game," says Marion Koopmans, a virologist at the Erasmus University Medical Center in Rotterdam, the Netherlands. "And the gambling is going on at too large a scale for comfort."

There are ways to improve our odds. For the best chance at preventing another pandemic, we need to get a handle on, and limit, the spread of the virus. Here, the US could have done a better job at limiting the spread in dairy cows, says Khan. "It should have been found a lot earlier," he says. "There should have been more aggressive measures to prevent transmission, to recognize what disease looks like within our communities, and to protect workers."

States could also have done better at testing farm workers for infection, says Koopmans. "I'm surprised that I haven't heard of an effort to eradicate it from cattle," she adds. "A country like the US should be able to do that."

The good news is that there are already systems in place for tracking the general spread of flu in people. The World Health Organization's collects and analyzes samples of viruses collected from countries around the world. It allows the organization to make recommendations about seasonal flu vaccines and also helps scientists . That's something we didn't have for the covid-19 virus when it first took off.

We are also better placed to make vaccines. Some countries, including the US, are already stockpiling vaccines that should be at least somewhat effective against H5N1 (although it is difficult to predict exactly how effective they will be against some future variant). The US Administration for Strategic Preparedness and Response plans to have "up to 10 million doses of prefilled syringes and multidose vials" prepared by the end of March, according to an email from a representative.

If we want our vaccine production process to be more robust and faster, we'll have to stop relying on chicken eggs.

The US Department of Health and Human Services has also said it -using .

Some question whether these vaccines should have already been offered to dairy farm workers in affected parts of the US. Many of these individuals have been exposed to the virus, , and some of them have become ill. If the decision had been up to Khan, he says, they would have been offered the H5N1 vaccine by now. And we should ensure they are offered seasonal flu vaccines in order to limit the risk that the two flu viruses will mingle inside one person, he adds.

Others worry that 10 million vaccine doses aren't enough for a country with a population of around 341 million. But health agencies "walk a razor-thin line between having too much vaccine for something and not having enough," says Khan. If an outbreak never transpires, 340 million doses of vaccine will feel like an enormous waste of resources.

We can't predict how well these viruses will work, either. Flu viruses mutate all the time, and even seasonal flu vaccines are notoriously unpredictable in their efficacy. "I think we've become a little bit spoiled with the covid vaccines," says Koopmans. "We were really, really lucky [to develop] vaccines with high efficacy."

One vaccine lesson we should have learned from the covid-19 pandemic is the importance of equitable access to vaccines around the world. Unfortunately, it's unlikely that we have. "It is doubtful that low-income countries will have early access to [a pandemic influenza] vaccine unless the world takes action," Nicole Lurie of the Coalition for Epidemic Preparedness Innovations (CEPI) said in for Gavi, a public-private alliance for vaccine equity.

And another is . Making vaccines might not be a problem-but convincing people to take them might be, says Khan. "We have an incoming administration that has lots of vaccine hesitancy," he points out. "So while we may end up having … vaccines available, it's not very clear to me if we have the political and social will to actually implement good public health measures."

This is another outcome that is impossible to predict, and I won't attempt to do so. But I am hoping that the relevant administrations will step up our defenses. And that this will be enough to prevent another devastating pandemic.