The H5N1 outbreak in the United States is heating up. Here’s what you need to know.

I’ve been writing about bird flu for some time now, but I realized I’ve never really talked about what it is, how people are getting sick, and why it’s a threat.

The past few months brought a few worrying twists to the bird flu story:

1. In January, the first person in the U.S. died from H5N1.
2. In February, there were two more separate spillovers into cows.
3. Also in February, two more people were hospitalized — a doubling of hospitalizations from bird flu.

All of this means that H5N1 is a long-term issue that’s not going to go away on its own — and it’s causing serious illness among some people who get sick.

I wrote an explainer for the Guardian about what the symptoms are, how the virus is spreading, and how worried we should be.

Here are a few points I wanted to highlight.

How deadly is bird flu?

Since 2003, there have been more than 950 reported cases of H5N1 globally, and 49% of patients have died.

But in the U.S. outbreak, the mortality rate has been much lower so far. There have been 70 confirmed cases, and several more probable cases, among people in the past year. One person has died.

That doesn’t mean that the virus is getting milder. The most likely reason is that we’re catching more cases.

“The virus can be really nasty for some people,” said Megan Ranney, an emergency physician and dean of the Yale School of Public Health.

We don’t know yet what puts someone at risk of getting really sick, Ranney said.

Flu viruses mutate and evolve quickly. If bird flu begins spreading between humans, there could be changes in how it sickens people, she added. “There’s really no way for me to say, if it becomes a pandemic, that we’re going to have the same case fatality ratio that we’re seeing right now.”

Is there a bird flu vaccine?

Yes, there are bird flu vaccines for people and for animals. But we don’t use them yet.

The official reasons why: there have been few hospitalizations and deaths in the US, there isn’t evidence of person-to-person transmission, and officials worry about hesitation over a new vaccine, according to Nirav Shah, former principal deputy director of the CDC.

But experts say the vaccine should be made available to farm workers, veterinarians and other people at risk.

Not a Doctor is 100% free. Sign up now for more updates on health, science, and technology.

In the meantime, does the seasonal flu shot help at all?

It probably doesn’t offer much protection against H5N1. But the seasonal flu shot is still an important part of preventing a bigger bird flu outbreak.

Here’s why: In rare cases when someone catches H5N1, they might catch the seasonal flu at the same time – and the two variants could mix together in a process called reassortment.

This could cause H5N1 to become more easily transmissible or cause more severe disease, said Meghan Davis, an associate professor of environmental health at the Johns Hopkins Bloomberg School of Public Health. “Brand-new viruses that can transmit easily are the ones that tend to cause epidemics or pandemics.”

Also:

“You should get the seasonal flu vaccine to protect you from seasonal flu,” Davis said.

Is bird flu going to get worse?

Any hopes that the current outbreak would simply pass through “have been dashed,” said Jennifer Nuzzo, a professor of epidemiology and the director of the Pandemic Center at Brown University School of Public Health.

“We have to be looking ahead to what would happen if this virus began spreading more easily between people,” Nuzzo has said. “If it could spread easily between people, we would be in a pandemic, and it would be around the globe in a matter of weeks.”

Experts expect another flu pandemic at some point. It might not be H5N1 – it might be a combination of H5N1 and a different flu variant, or a different type altogether.

That means it’s important for officials to take action: preparing vaccines, treatments and tests, and strengthening healthcare systems.

And it helps immensely when everyday people ask their elected officials to take these actions and to invest in public health before the next crisis hits.

If you found this helpful, please share on social media or forward to a friend!

Top photo: Grassroots Groundswell