Hey readers,
Dylan Scott here. Since Covid-19 took the world by surprise, scientists and policymakers have been striving to make sure the mistakes that led to the US having one of the highest pandemic death rates in the world are not repeated.
Progress has been fitful. Negotiations over an international pandemic agreement that was supposed to have been ratified this spring stalled in May, and the world's nations have given themselves another year to hammer out a deal.
Meanwhile, the threat of bird flu looms, a reminder that another pandemic will come sooner or later. Experts are urging health authorities around the world to do whatever they can to prevent the H5N1 virus from starting the next global health emergency.
But the truth is, humanity has a limited ability to prevent a pandemic. Stopping pandemics before anybody gets sick would require marshaling immense resources to tackle intractable problems — like climate change and ecological destruction — that create the conditions for disease spillover from animals to humans in the first place. Factory farming is one well-known yet hard to reform risk factor for pandemics, a risk playing out right now amid the H5N1 outbreaks at poultry and dairy farms across the US.
And being prepared for what to do once people get sick is inevitably a challenge, too. The unpredictable mutations necessary for a pathogen to start a pandemic restrict our readiness for a scenario in which it spills into the human population and sparks an outbreak.
Arturo Casadevall, who studies infectious diseases at Johns Hopkins University, put it succinctly in a 2024 Journal of Clinical Investigation essay on what the past century of pandemics has taught us: "All pandemics surprise humanity."
Call it the pandemic paradox: To ignite a worldwide pandemic, a virus would need to evolve to the point that it can easily transmit between humans. Any vaccines or treatments or tests we come up with now, before the emergency actually begins, may not work after that next leap of evolution.
That makes it especially important to understand what is in our control and prepare accordingly. Contingency plans can try to anticipate the problems we might encounter in a public health emergency, helping us war-game how we would disperse protective gear to the public and medical professionals and increase hospital capacity. We could draw up vaccine manufacturing plans and set up fast-track applications for federal approval. We could also do more to monitor emerging threats in real time to identify a public health crisis as early as possible.
The most realistic hope for our preparedness plans is to have an effective playbook once a pandemic starts. We can't expect to stop an infectious disease crisis from arising in the first place, nor can we expect to have perfectly calibrated countermeasures that we can pull off the shelf at a moment's notice. Nature necessarily starts with the upper hand.
The pandemic paradox
With the world now on high alert for H5N1, it can be easy to forget this simple fact: The reason we are not in a pandemic already is because the virus is still not very good at infecting humans and transmitting between them. The WHO reiterated this month that the public health risk from bird flu remains low.
But in that warning is an implied "for now." After all, the reason for recent concern is that the avian flu has adapted to better spread among cattle and dozens of other mammal species such as domestic cats and wild minks.
Still, while cows are much more closely related to humans than birds, it would take another evolutionary leap for H5N1 to become easily transmissible between humans and set off a wider outbreak.
The worst-case scenario would be a virus evolving to be more transmissible while also carrying a high risk of death. H5N1, with its 50 percent fatality rate in the roughly 900 human cases reported over the last 20 years, has been sitting in this pandemic staging area for years.
How could it make the jump? One concerning scenario would be if avian flu started spreading among pigs, a species that is genetically even closer to humans than cows and cats, and has long been considered a petri dish for dangerous pathogens to evolve to better infect humans.
"There's more experience with rearrangement of viruses in pigs, and it could go on to infect humans," Tina Tan, who studies infectious diseases at Northwestern University, said in a recent Infectious Diseases Society of America briefing.
Addressing this very real threat demands balance as we try to monitor H5N1 for signs of increased transmissibility without overreacting and neglecting more immediate health threats.
As STAT's Helen Branswell recently explained, responding to questions about why we aren't already manufacturing millions of vaccines, starting mass production of one of the H5N1 vaccine prototypes already developed would mean pausing the production of next year's seasonal flu vaccine — since both would have to be made in the same factories — for what is now still a theoretical risk.
Likewise, manufacturing millions of diagnostic tests when we can't be sure they'll be accurate if the virus evolves could end up being a costly waste of time and resources.
"There are people out there now who are saying we should be making rapid tests so that all Americans have them when we need it. Let's wait. This virus is going to change. It will need to change," Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health, told me. "We don't yet know if doing that is actually the path to having the tests when we need them."
There are still opportunities to put the lessons of Covid-19 to use in monitoring H5N1's pandemic potential. Experts cite the rapid genomic sequencing of new H5N1 variants in mammals as one example of the pandemic's investments paying off, after $1.7 billion was pumped into lab infrastructure over the past few years. That capacity helps scientists understand how the virus is mutating and provides a baseline for developing tests and vaccines. We have also expanded wastewater surveillance networks that could be deployed as an early warning system.
But the US public health response to bird flu so far has had its shortcomings, too: Monitoring the developing risks on factory farms remains the weakest link in our surveillance system. Experts generally agree there isn't enough testing of farm animals and the human workers who come into close contact with them. Better testing would allow us to more speedily detect a sudden uptick in bird flu activity and put emergency measures into action as soon as the situation demands them. The federal government has attempted to entice farms to test with incentives (rather than mandates), but the industry has largely resisted taking such measures.
The pandemic paradox explains why we'll always start the next emergency a little behind. But there's a lot we can do to make sure we catch up as quickly as possible.
—Dylan Scott, senior correspondent and editor
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