DEFCON 3 for H5N1. (DEFCON 1 is the worst.)

Why my threat assessment has changed.

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Among all the bird flu cases in humans during the summer and fall of 2024, there was only one that really worried me. It was the case of an otherwise healthy teenager in British Columbia, Canada. Somehow, the boy acquired bird flu (H5N1) and he became critically ill, apparently requiring a medically induced coma and a breathing machine.

Until December 18th, there had been 65 cases of H5N1 in the United States. All of these cases were mild. In addition, there were probably hundreds (if not thousands) more that went undetected, according to both common sense and CDC antibody testing data. These cases were almost certainly mild if not asymptomatic. If there had been an uptick in severe disease (even in young healthy people), the CDC would have been able to detect that.

But on December 18th, a second case bothered me: the first severe case of H5N1 in a US resident, which occurred in an older man exposed to birds, and which was announced by the CDC. This case raised my concern, for some obvious and some non-obvious reasons. I began to write an Inside Medicine about this but realized (as sometimes occurs) that the piece probably warranted a broader audience. So, I sent it to Slate where it was published today. Please have a look at it and let me know if you have questions.

All told, I think a severe case of H5N1 coming on the cusp of the forthcoming peak of flu season merits an increase in our threat assessment of the overall situation. I’d say we are now at the equivalent of DEFCON 3 with H5N1. DEFCON 3 is defined by Military.com as “as a standby level of alert, and it is the highest level of alert during peacetime.” Late March of 2020 in New York City was what I’d call DEFCON 1.

Where are we going from here?

Nobody knows what will happen next. Are we on the precipice of another horrible pandemic? Or will we dodge a bullet? As I wrote on Threads and Bluesky, it’s okay to admit that we don’t know whether H5N1 will cause a major emergency in humans. What is undeniable is that our current circumstance is akin to a game of Russian Roulette—and there have never been more bullets in the chamber. As I outlined in the Slate piece, I’m worried about the possibility of a novel variant of H5N1 emerging from a coinfection—that is, a single person getting seasonal flu and bird flu at the same time, which is a recipe for a potentially horrific flu pandemic.

Walking the line.

The trick here is that we want to balance concern against something called “alarm fatigue.” We want the public to be aware of a potential threat, but we don’t want to say we are in DEFCON 1 (or even DEFCON 2) if ground conditions do not support such a claim. If we tell the public that everything is an emergency, pretty soon nothing is. We can’t cry wolf, lest the public tune us out and we regret it later.

Action items.

Regardless, the current action items are mainly directed at governments—things like increased testing in high-risk settings (farms) and better PPE for high-risk people (farmworkers). At some point, the federal government should also consider increasing our supplies of H5N1 vaccines and consider administering them to high-risk individuals like farmworkers (in whom most of the US cases have been detected so far). When this will be done is unclear, and there’s no single indicator or threshold for taking this action. One bellwether to watch for is any evidence of human-to-human spread, something we have not detected so far, thankfully.

What can the public do? Not a lot, other than the usual—which is to take whatever precautions you’d normally take to avoid a respiratory illness. But, as I’ve said before, there’s one thing some people can do: Get your seasonal flu shot now if you haven’t already. We’re rapidly headed into peak flu season and these seasonal shots tend to work well within a week or two, temporarily decreasing the risk of infection and (for a longer period) severe illness. In the present environment, that action could be even more important because you are less likely to have a coinfection if you’re protected against one of the viruses.

Want a seasonal flu shot? It’s not too late! Find one here!

What are your questions about H5N1? Join the discussion in the Comments section.