Up until now, most of us have only really seen the effects of this in our grocery bill.

But then, on January 6th, someone in Louisiana died.

It was the first reported human death from avian flu in the United States, which is pretty alarming.

But the TLDR here is you don't actually have to panic.

So far, there have only been 67 human cases in the United States, and infections are typically very mild.

It's unlikely this will be another COVID.

And maybe that's all you care to know.

That being said, avian flu isn't going anywhere anytime soon.

It's been found in every U.S. state and on every continent except Australia.

Public health experts are concerned, because there is a chance this could get worse.

So what I wanted to know was this, if we're not worried now, is there a point when we should be?

Avian flu viruses are naturally found in waterfowl, like geese or ducks.

H5N1, the type of avian flu circulating right now, was first identified in geese in 1996 in China.

In 2020, a variant of that original strain was found in wild birds in Europe.

By late 2021, it was in the U.S. and Canada.

Typically, a duck, goose, or other natural host shows no symptoms, but can spread the virus through dropping saliva or mucus.

When an infected bird comes in contact with poultry is when we start to see disease.

And this is usually categorized in one of two ways.

The first is low pathogenicity, which shows very little sign of illness.

Maybe a chicken will lay less eggs or stop laying eggs altogether.

The second is high pathogenicity, which is incredibly infectious and can result in 100% death rate.

You can guess which one we're currently dealing with.

When either version of avian flu turns up on poultry farms, it has devastating effects.

Farmers are often forced to cull all animals to prevent further spread. 4.2 million chickens on Iowa egg farms as of last July, 100,000 ducks on Long Island in January, another million chickens in the United Kingdom.

The economic loss to farmers is in the billions.

But over 100 million dead domesticated birds later and the virus is still spreading.

The reason we're concerned now about this particular avian flu is that it is spilling over more often than we see other avian flu viruses do.

This particular gene constellation seems to be causing much more ability to spread across species areas.

Everybody I spoke to for this story really wanted to drive home this point.

This virus has affected an overwhelming diversity of animals.

Experts are calling it panzootic, a pandemic among animals.

It's been detected in nearly 500 species of birds worldwide, including the endangered California condor, and at least 70 species of mammals, seals, minks, foxes.

It's killed sea lions by the thousands, bears and pigs and dolphins, otters, ferrets and cats, and most recently, dairy cows, which is weird and concerning for two main reasons.

One, where it's being found in the cow, influenza viruses, for humans, tends to be a respiratory pathogen.

This virus in particular, it's replicating in a mammalian species in a tissue site that's not common for influenza.

Avian flu is being found in especially high levels in milk.

Luckily, pasteurization, the simple process of heating milk before packaging it, keeps consumers safe from exactly this sort of thing.

Now, the second problem is more obvious.

Avian flu in dairy cows brings avian flu closer to humans, but that is a bigger problem than a person just getting sick.

Here's why.

The flu virus changes in two ways, mutation and reassortment.

The mutation is sort of like what happens every year with seasonal flu viruses.

Every year, as the virus replicates in us, the virus will change.

This is the new version of the same virus.

It just made a mistake while replicating itself.

Reassortment, on the other hand, is when two different viruses meet in a cell and swap genetic material.

Let's say this virus infected a human during flu season, and you have sick kids at home and all of a sudden you also have human seasonal flu, and you have this H5N1 because you work on a dairy farm.

Now, all of those genomes, while distinct, are related, right?

They're all influenza.

And they can reassort or intermingle within that cell and generate new viruses.

Reassortment of avian flu resulted in two pandemics, in 1957 and 1968.

And reassortment of swine flu resulted in the 2009 swine flu pandemic.

The reason we worry about that so much is that seasonal influenza viruses are epidemiologically very successful.

They spread so easily from person to person.

Now, what does it take for a virus to cause a pandemic?

You have to have a virus that is novel, that infects humans and causes disease.

The population has to be susceptible.

The way we usually think about it, it means that you don't have antibodies to that subtype.

But very importantly, the virus has to be able to spread efficiently from person to person through sustained chains of community transmission.

This is generally what public health experts are on the lookout for, and why monitoring this virus is really important.

So what the H5N1 viruses have are that they're novel, they infect people, they cause disease, and the population is susceptible.

But they have not yet demonstrated the ability to spread efficiently from person to person.

If this virus starts spreading between humans, then our problems have extended beyond dead birds and egg prices.

Luckily, there are still a few other things on our side here.

For one, the disease so far is mild in humans, and two, reassortment in humans is way less likely than it is in pigs or birds for some reason.

As for vaccines, our seasonal flu shot is very specific, so it's unlikely it will give us any immunity to this.

However, previous exposure to the flu virus might give us a slight edge.

The people that should be more concerned and more proactive are the ones that are in public health, decision-making and public health funding and so on.

The best we can do right now is be aware of what's happening.

As it stands, the avian flu is getting a lot of chances to change and become a bigger problem for humans.

We haven't stopped it yet.

I'm far less certain that we can put the genie back in the body.

Well, what a comforting way to end a video after telling you not to panic.

Anyway, I sincerely hope that this was helpful.

After two years of following this story and thinking of all the different ways I could get over it, I ultimately just landed here, a piece that tries to answer your biggest questions without freaking you out too much.

I've been at Vox for over seven years, and I've come to realize that I really try to answer two types of questions.

The dire ones that feel like they need answering right now, and some that just spark curiosity to remind us that, sure, things are chaotic, but the world is also wild and full of wonder.

If you like that mission and want to help, you can join our membership program at vox.com slash memberships.

Thanks for being here.

I'm your host, Vox Machina.