The dawn of a new year often brings with it the potential emergence of novel viral threats.

Viruses from the past are in a constant state of evolution, adapting and changing over time. Our warming planet, coupled with its burgeoning population, increases the likelihood of humans encountering a broader array of viruses. With global travel now more accessible than ever, these viruses can hitch a ride with human hosts, spreading swiftly across international borders.

Patrick Jackson, an infectious disease expert at the University of Virginia, is particularly vigilant about certain viruses as we look toward 2026. His focus is on those that may unexpectedly surge in new regions or in larger numbers than anticipated.

Among these, Influenza A remains a persistent concern. This virus, notorious for its adaptability, affects a wide variety of animals and possesses the capability to mutate swiftly, posing an ongoing challenge to public health.

Influenza A: on the cusp of a pandemic 

Pictured above, a hazmat worker cleans a struck in a quarantine zone during a bird flu outbreak in Victoria, Australia, in 2024

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 US and subsequently became established in herds in several states. In the current outbreak, 71 cases have been detected in humans and one person has died in the US. 

The crossover of the virus from birds to mammals created major concern that it could become adapted to humans, and some studies suggest there have already been many cow-to-human transmissions. 

While almost all patients in the current outbreak had direct contact with infected birds or cattle, a patient in Missouri became the first to be infected without any exposure to these animals in 2024. 

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.

As for more common variants of the flu, H3N2 subclade K, dubbed ‘super flu,’ has swept through the US and shown ‘very high’ activity in 14 states. 

The latest CDC data shows 19 percent came back positive during the week of December 27, finally declining after weeks of surges.

The CDC estimates there have been at least 11 million flu illnesses, 120,000 hospitalizations and 5,000 deaths this season.

Mpox: worldwide and liable to worsen

The above 2024 image shows a patient in the Democratic Republic of the Congo (DRC) infected with Mpox, formerly known as monkeypox

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.

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 the 2022 outbreak, clade II mpox has become established around the world. Several countries in central Africa have also reported an increase in clade I mpox cases since 2024. 

Since August 2025, four clade I mpox cases have occurred in the US, including three people who did not travel to Africa. Clade I has a mortality rate of 10 percent.

Cases of Clade I Mpox in Africa are not closely tracked, but the most recent estimates from the CDC in late 2024 have counted nearly 46,000 suspected cases in the Central and East Africa, namely in the Democratic Republic of the Congo (DRC), and more than 200 deaths. 

It is unclear how mpox outbreaks in the US and abroad will continue to evolve in 2026. 

Oropouche virus: insect-borne and poised to spread 

Pictured above is a biting midge, which carries Oropouche virus (stock image)

Oropouche virus was first identified in the 1950s on the island of Trinidad off the coast of South America. The virus is carried by mosquitoes and small biting midges, also known as no-see-ums. 

Most people with the virus experience fever, headache and muscle aches. The illness usually lasts just a few days, but some patients have weakness that can persist for weeks. The illness can also recur after someone has initially recovered. 

There are many unanswered questions about the Oropouche virus and the disease it causes, and there are no specific treatments or vaccines. For decades, infections in people were thought to occur only in the Amazon region. 

However, beginning in the early 2000s, cases began to show up in a larger area of South America, Central America and the Caribbean. 

Cases in the US are usually among travelers returning from abroad. About 100 Americans import the disease every year, though exact figures are not closely tracked. During 2024-2025, the US saw 110 human cases, CDC data shows. 

The cases were seen in Florida, New York, New Jersey, Kentucky, Wisconsin, Colorado and California. 

In 2026, Oropouche outbreaks will likely continue to affect travelers in the Americas. The biting midge that carries Oropouche virus is found throughout North and South America, including the southeastern US 

The range of the virus could continue to expand. 

Even more viral threats

Chikungunya is transmitted to humans by Aedes aegypti and Aedes albopictus mosquitoes infected with it 

A number of other viruses pose a risk in 2026.

Continuing global outbreaks of chikungunya virus, a mosquito-borne illness, may affect travelers, some of whom may want to consider getting vaccinated for this disease.

Chikungunya is transmitted to humans by Aedes aegypti and Aedes albopictus mosquitoes infected with it and causes sudden high fever and severe, often debilitating, joint pain. 

Other common symptoms include rash, muscle pain, headache and fatigue. 

Measles infected more than 2,000 people in the US last year, the highest number in three decades (stock image) 

Measles cases continue to rise in the US and globally against the backdrop of decreasing vaccination rates. In 2025, more than 2,000 cases of measles were recorded in the US, the most in three decades.

Vaccines are up to 97 percent effective against a measles infection, but, among unvaccinated people, nine in 10 of those exposed to the virus become infected. 

HIV is also poised for a resurgence, despite the availability of effective treatments, due to disruptions in international aid. 

And as-yet-undiscovered viruses can always emerge in the future as humans disrupt ecosystems and travel around the world. 

Around the globe, people, animals and the wider environment are dependent on each other. Vigilance for known and emerging viral threats and the development of new vaccines and treatments can help keep everyone safe. 

This article is adapted from The Conversation, a nonprofit news organization dedicated to sharing the knowledge of experts. It was written by Patrick Jackson, an assistant professor of infectious diseases at the University of Virginia, and edited by Emily Joshu Sterne, a senior health reporter at Daily Mail.