A new year might mean new viral threats.
Old viruses are constantly evolving. A warming and increasingly populated planet puts humans in contact with more and different viruses. And increased mobility means that viruses can rapidly travel across the globe along with their human hosts.
As an infectious diseases physician and researcher, I’ll be keeping an eye on a few viruses in 2026 that could be poised to cause infections in unexpected places or in unexpected numbers.
Influenza A – on the cusp of a pandemic
Influenza A is a perennial threat. The virus infects a wide range of animals and has the ability to mutate rapidly. The most recent influenza pandemic – caused by the H1N1 subtype of influenza in 2009 – killed over 280,000 people worldwide in its first year, and the virus continues to circulate today. This virus was often called swine flu because it originated in pigs in Mexico before circulating around the world.
Most recently, scientists have been monitoring the highly-pathogenic avian influenza H5N1 subtype, or bird flu. This virus was first found in humans in southern China in 1997; wild birds helped spread the virus around the world. In 2024, the virus was found for the first time in dairy cattle in the U.S. and subsequently became established in herds in several states.
Avian flu has spread across dairy herds in the U.S.
USDA Agricultural Research Service via AP
The crossover of the virus from birds to mammals created major concern that it could become adapted to humans. Studies suggest there have already been many cow-to-human transmissions.
In 2026, scientists will continue to look for any evidence that H5N1 has changed enough to be transmitted from human to human – a necessary step for the start of a new influenza pandemic. The influenza vaccines currently on the market probably don’t offer protection from H5N1, but scientists are working to create vaccines that would be effective against the virus.
Mpox – worldwide and liable to worsen
Mpox virus, formerly called monkeypox virus, was first discovered in the 1950s. For many decades, it was seen rarely, primarily in sub-Saharan Africa. Contrary to its original name, the virus mostly infects rodents and occasionally crossed over into humans.
Mpox is closely related to smallpox, and infection results in a fever and painful rash that can last for weeks. There are several varieties of mpox, including a generally more severe clade I and a milder clade II. A vaccine for mpox is available, but there are no effective treatments.
Mpox has spread around the world.
NIAID/Wikimedia Commons, CC BY-SA
In 2022, a global outbreak of clade II mpox spread to more than 100 countries that had never seen the virus before. This outbreak was driven by human-to-human transmission of the virus through close contact, often via sex.
While the number of mpox cases has significantly declined since…
