Here we are, on the cusp of the midway point in a decade that has been, in global health and infectious diseases terms, a lot.
The 2020s started with the most severe pandemic since the 1918 Spanish flu. Just as the worst of Covid-19 was starting to ease, the world was introduced to mpox, a cousin of smallpox that went from occasionally infecting people who had contact with infected rodents in forested parts of West and Central Africa to spreading from person to person in Europe, the Americas, and beyond, mainly via sex. In 2024, bird flu became cow flu, or moo flu, as some researchers like to refer to it. Between outbreaks in dairy cows, outbreaks in poultry operations, and outbreaks in wild birds, the amount of H5N1 virus in the environment has reached unsettling levels.
So what does 2025 have in store for us on the global health front? Unfortunately, it doesn’t feel like the 2020s are ready to cut us any breaks. The list of things we at STAT are watching is long, but here are three that we’re pretty sure will be grabbing headlines in the new year.
What’s going to happen with H5N1 bird flu?
H5N1, a viral family that traces its lineage back to an influenza virus isolated in China’s Guangdong province in 1996, has often had the scientific world on edge over the ensuing three decades. After a period of relative quiet in the second half of the previous decade, it has roared back in the past couple of years, infecting an astonishing array of mammals. (Astonishing because this is, after all, a bird version of flu.) In 2024, the world discovered the virus was transmitting among dairy cows in the United States, a stark reminder that you should always expect the unexpected with H5N1.
Flu viruses that don’t circulate among people could trigger pandemics, if they acquire the capacity to easily infect us. There are two ways they can make that jump. The first is by mutation — the acquisition of random genetic changes that would let a virus currently suited to infecting birds become a virus that can easily infect people. Spending time infecting a mammalian species like cows could set H5N1 on that path.
The second is a process called reassortment. When different flu viruses co-infect a host — a duck, a pig, maybe a cow or a person — they can swap genes, giving rise to hybrids of the original viruses. With flu season settling in across the country, some farmworkers will contract seasonal flu, and some of them will go to work sick. If someone were to catch both seasonal flu and H5N1 at the same time, the former could give the latter some genes that could make H5N1 transmissible to and among people.
Will that happen? There’s no way to estimate the odds. If H5N1 does start a pandemic, would it be a deadly one? That’s another unanswerable question. But having this virus circulating in dairy cows is like allowing Mother Nature to keep throwing dice at a craps table. The house normally wins. But it doesn’t always.
In the time since H5N1 found its way into cows it has been making regular forays into people. By Dec. 23, the Centers for Disease Control and Prevention had confirmed 65 human infections in 10 states in 2024. And that’s only part of the story. There were plenty of anecdotal reports of dairy workers with similar symptoms who didn’t go for testing. Studies looking for missed cases by studying the blood of exposed people have found more people have been infected than have been confirmed as cases. With the exception of a case in Louisiana recorded earlier this month, all known cases in the U.S. have been mild.
From the start, the dairy industry has treated this outbreak as if it is merely a cow problem, one to be soldiered through. The U.S. Department of Agriculture hasn’t challenged that in any significant way, asserting without any discernible evidence that the virus will eventually burn itself out. Only recently has the department decided to actively go looking for the virus, with a mandatory bulk testing program that started only in six states but has since been expanded to seven more.
Whether the virus will burn itself out in cows is yet another of the unanswerable H5N1 questions. States that had infected herds early on — Kansas, for example — haven’t reported new infections for months. Is that because there are none? Or because farmers won’t test their cows? These questions have answers, but getting them requires political will that, in a presidential election year, has been absent.
An answer may come from California, the country’s largest dairy producer, where the virus has stormed through more than two-thirds of the state’s herds — 675 —since the first infections were detected at the end of August. California is actively looking, both for infections in cows and infections in people, and it is reporting its findings. Presumably if the virus starts to cycle through herds for a second or third time, that will be detected there.
Meanwhile, studies of the specific version of the virus currently circulating suggest there may be fewer hurdles standing in the way of this iteration of H5N1, known as clade 2.3.4.4b, acquiring the capacity to easily infect people than there were for earlier versions of the virus.
Is the stage being set for an H5N1 pandemic? We don’t know. But we’ll continue to watch this story closely.
Can the spread of mpox be stopped?
In the spring of 2022, health authorities in Britain startled the world when they announced they had detected local transmission of monkeypox, a disease caused by a member of the poxvirus family. It soon became apparent that the virus was being transmitted from person to person, in multiple countries, through sexual contact. Mpox, as the disease has since been renamed, had found an express lane to make its way around the world.
In 2022, the outbreak was largely occurring in communities of gay, bisexual and other men who have sex with men. Behavioral changes and deployment of vaccines developed to protect against smallpox (the viruses are related) slowed the spread of the virus, though cases of that version of mpox, called clade IIb, are still popping up in parts of the world where mpox previously was not found.
In 2024, the mpox story took a new unwelcome twist. Human-to-human spread of two other versions of the virus, clades Ia and Ib, took off in a number of African countries. They, too, are being spread through sex in some cases; in others, household contacts of infected people are contracting the virus as well.
Transmission of clade I viruses outside of Africa has not yet reached the levels seen in 2022 with the clade II viruses. But a number of African countries are struggling to contain their spread. Twenty countries on the continent have reported nearly 14,000 laboratory-confirmed cases and 60 deaths this year; lab-confirmed cases capture only a portion of the actual transmission. Globally there have been nearly 22,500 confirmed cases and 78 deaths reported from 82 countries this year.
The world’s capacity to make mpox vaccine is based on the size of the previous market for the product. The purpose of that market was not to vaccinate at-risk people in multiple countries, rather it was to produce vaccine for the emergency stockpiles that wealthy countries hold in case smallpox is released as a weapon of bioterrorism. As a result stores of the main product available, Bavarian Nordic’s two-dose Jynneos vaccine, are limited and its cost is high. Donated doses are being used in a number of countries, but need exceeds supply.
The global vulnerability to mpox stems from the decisions decades ago to stop vaccinating against smallpox, a virus that was declared eradicated in 1980. Cessation of those vaccination efforts has created a growing pool of children, adolescents, and adults with no immunity to poxviruses. The vast majority of the confirmed cases since 2022 have been in people aged 18 to 49, according to data collated by the World Health Organization.
In July 2022, the WHO declared the spread of mpox a public health emergency of international concern. It lifted the emergency in May of 2023, by which point international spread of mpox had slowed, but had not stopped entirely. In August of this year, a second mpox PHEIC was declared.
As the world looks to 2025, a question begs answering: Can spread of these viruses be beaten back? Or is human-to-human transmission of mpox a fact of life in a world with declining immunity to poxviruses?
Is the sun starting to set on American influence in global health?
The first Trump administration served notice in July of 2020 — just months into the Covid-19 pandemic — that it intended to withdraw the United States from the WHO. Before the withdrawal could be finalized Donald Trump lost his bid for reelection. On his first day in office, President Joe Biden rescinded the withdrawal notice.
Fast-forward four years: A second Trump presidency is about to begin. The incoming administration is already making noises about announcing a U.S. withdrawal from the WHO on day 1. The soon-to-be-reinaugurated president denounced the Geneva-based global health agency’s handling of the Covid pandemic, accused it of being in the thrall of China, and in general feels that the U.S. carries more than its share of the cost of international institutions.
The WHO’s constitution does not include provisions for member states to withdraw. But the resolution that Congress adopted in 1948 allowing the U.S. to join the WHO lays out the rules under which the country can revoke its membership. It requires a one-year notice and the payment of any outstanding financial obligations before leaving. The U.S. dues for 2025 amount to slightly more than $130 million, far more than the dues owed by any other member country. (China’s assessed contribution, as WHO’s membership dues are called, is second, at about $87.6 million.) Dues are only a portion of the funding affluent nations like the United States provide the WHO. In terms of voluntary contributions — which are typically earmarked for specific programs the donor wants to support — the U.S. is also the biggest single giver. Overall, the U.S. is the WHO’s largest member state contributor.
The WHO has been trying to diversify its funding sources, but losing the U.S. would be an enormous blow to the agency. In addition to the loss of funding, it would call into question the role the U.S. plays in myriad programs run by the WHO, such as the selection of virus strains for flu vaccine or the country’s contribution — in terms of human expertise — to health emergency responses.
No country — let alone one that plays such a big role in the agency — has ever withdrawn from the WHO before. “We don’t know what all breaks if we pull out,” a global health expert told STAT.
One likely outcome: Far fewer Americans working in the WHO’s Geneva headquarters, where the American contingent has long been large. In fact, a U.S. withdrawal could actually effectuate the situation Trump has complained about — greater Chinese influence in Geneva. It’s hard to imagine China, the European Union, or other major contributors to the WHO wouldn’t demand the seats at the tables that U.S. scientists currently hold.
The status of the U.S. membership in the WHO is not the only place where American influence in the global health sphere could decline. The potential for big cuts to research efforts (at the CDC) and funding (through the National Institutes of Health) could drive scientists to seek new homes.
Some in Europe are already anticipating a scientific exodus. Isabella Eckerle, director of Switzerland’s Geneva Centre for Emerging Viral Diseases, has been predicting European institutions are about to face “a golden opportunity” to recruit top-flight U.S. talent.
“I believe at least in the infectious disease research field the U.S. will see an unprecedented brain drain of academics,” Eckerle said on the social media network Bluesky, suggesting the influx she predicts would “boost European infectious disease research and drive innovation in tools, data science, drug and vaccine development etc…. [S]trategically, major win for Europe for coming decades!”
All this to say that if you have any downtime scheduled over the holidays, rest up. 2025 could be pretty rock ’n roll.