A new strain of H5N1 virus, also known as bird flu, has been found in herds of dairy cows in nine states across the country. So far, only two people have been infected with this strain due to exposure to cows: one farm worker in Texas and one in Michigan, both of whom have since recovered fully. But the large number of infected dairy cows, their close proximity to humans, and the historical precedent for flu to jump from one host to another have scientists and health officials concerned.
We asked Andrew Pavia, MD, chief of the Division of Pediatric Infectious Diseases at University of Utah Health and an infectious disease physician at Intermountain Health, about why health experts are keeping such a close eye on the latest wave of avian flu and what we can do to keep safe.
Is this strain of bird flu dangerous to humans?
In the current iteration of H5N1, we've not seen a lot of human disease. Most of the cases that have been documented in humans due to this strain of H5N1 have been fairly mild. But there's relatively poor tracking of the disease around the world, so there's a lot of uncertainty.
But it's probably safe to say that, right now, the virus is not very effective at transmitting to humans. There's been no human-to-human transmission. So in its current state, by itself, the virus is not posing much of a threat. But that can certainly change.
So why are health officials on alert?
The one thing you can predict about flu is that it's unpredictable. It has unique evolutionary pathways because it can recombine gene segments [the pieces of DNA that make up genes] as well as mutate. And what we've seen in the last roughly two years is very alarming to people who study flu.
The risk to humans right now is very low, but that could change in a nanosecond with a recombination event (a kind of genetic change that could potentially allow the virus to spread from human to human, for instance). That may never happen. But it could also happen next week. We need to be prepared and we need to take it seriously without inducing panic.
What do we know about where H5N1 came from?
H5N1 is changing rapidly. It’s gone from a disease that was very lethal for birds into one that infects mammals. Initially, we saw sporadic cases in mammals like foxes and a bear that had probably been eating dead birds. Then there were outbreaks on mink farms where there was probably mink-to-mink transmission, and then these weird outbreaks among seals and sea lions where there was at least a strong suggestion that it was spreading from seal to seal.
When a related strain of H5N1 first appeared in humans in Hong Kong in 1996, it was quite lethal. Between then and 2017 or so, there were something in the range of 900 documented cases, and there were almost 500 deaths. So, in its original form, it was a very dangerous virus. Very few people caught it, but when they did, they didn't do well.
What should people do to avoid getting sick?
Don’t drink raw milk:
There’s not a lot of threat to people right now. The potential threat out there is raw milk. Infected cows have huge amounts of virus in their milk, and we know that cats that have drunk infected milk have gotten very sick with about a 50% mortality rate. Based on that, there’s a good chance that drinking infected raw milk could be quite dangerous.
Don’t eat fresh raw milk cheese:
We don’t have as much information about raw milk cheese, but most pathogens in raw milk cheese don’t survive aging. So if you do like raw milk cheeses, you should only eat aged raw milk cheeses.
Keep away from dead birds:
There is also still an ongoing outbreak among birds, and if you find dead birds, you should be very careful in handling them. Either leave them alone and call wildlife authorities, or wear gloves and a mask and put them in a bag and inquire about what to do with them. You should keep your animals, like dogs, away from dead birds, too.
If more people become infected, what treatments are available?
We have antivirals for flu, like Tamiflu and Xofluza, and to date almost every H5 virus that’s been tested is sensitive to those drugs. The concern is that if we have a huge outbreak, would we have enough in a timely manner, and can we get them to people quickly? But right now, we have the ability to treat people with drugs that we think would work very well.
There are also vaccines against H5 that are kept in stockpile in small supplies: hundreds of thousands of doses. And there’s bulk agents that would allow the production of maybe a few million doses within a few months. But we have a lot of work to do in terms of having emergency production capacity.
mRNA vaccines for H5N1 are also being studied. If they work, they can be produced faster—and they can be adopted faster than our existing vaccines. But until the tests are run with H5N1 mRNA vaccines, we don’t know if that’s viable.