The world is facing a complex viral landscape, with three viruses – avian influenza H5N1, mpox, and Oropouche – drawing increasing concern from infectious disease specialists. This comes as the globe continues to grapple with the lingering effects of the COVID-19 pandemic.
A confluence of factors, including global warming, population growth, and increased human mobility, is creating conditions favorable for viral evolution and rapid spread, according to experts. Patrick Jackson, an adjunct professor of Infectious Diseases at the University of Virginia, highlighted these three viruses as particularly noteworthy in 2026.
Whereas distinct, all three have recently expanded their geographic reach, prompting calls for strategic vigilance rather than alarm. The World Health Organization (WHO) is actively monitoring the situation and coordinating international responses.
Oropouche Virus: A Growing Threat in the Americas
Perhaps the least known of the three, the Oropouche virus is transmitted by tiny midges and causes flu-like symptoms. Initially identified in Trinidad and Tobago in the 1950s, it was long considered confined to the Amazon region. Still, since the 2000s, it has been spreading across South and Central America, and the Caribbean.
The virus resurged in 2023, and in 2024, deaths linked to Oropouche were documented for the first time in Brazil. By August 2025, Brazil accounted for 90% of cases in the Americas, spanning 20 states, with five confirmed deaths – four in Rio de Janeiro and one in Espírito Santo. Cases linked to travelers have also begun to appear in Europe, according to IFL Science. Cases of vertical transmission – from mother to child – have been reported, and a possible link to microcephaly and fetal deaths is under investigation.
The virus’s vector, a biting midge, has adapted to a wide range of habitats across the continent. Currently, there is no vaccine or specific treatment available. On January 5, 2026, the WHO proposed accelerating the development of prevention and control tools against Oropouche.
Avian Influenza H5N1: Crossing the Species Barrier
Avian influenza has long been a concern due to its rapid mutation rate and ability to infect various species. The 2009 H1N1 swine flu pandemic caused over 280,000 deaths in its first year. Now, attention is focused on H5N1. The virus moved beyond birds in 2024, with its first detection in U.S. Dairy cows. This species jump raised concerns, particularly as the pathogen reappeared in herds across multiple American states.
Studies suggest multiple cow-to-human transmissions, often without apparent symptoms. A case of avian influenza was confirmed in a commercial farm in Brazil in 2025. The primary fear is that the virus will adapt to transmit efficiently between humans, a necessary step for a new pandemic to emerge. As of early 2026, the U.S. Centers for Disease Control and Prevention (CDC) has recorded 71 human cases and two deaths since 2024, with no evidence of sustained community transmission.
Vaccines specific to this strain are under development, as current formulations may not provide sufficient protection. Brazil’s Butantan Institute is conducting pre-clinical safety studies on a potential vaccine.
Mpox: Two Clades in Global Circulation
For decades, mpox was a rare disease, largely confined to specific regions of Africa. This changed in 2022, when the clade IIb strain spread to over one hundred countries. Transmission through close physical contact, often during sexual activity, established this variant as a recurrent virus in many nations.
Concurrently, since 2024, Central African countries have seen a rise in infections from clade I, considered more severe. The United States has recently reported cases in individuals with no history of travel to Africa. While a vaccine exists, there is no specific treatment, and experts warn that viral evolution throughout 2026 could present new public health challenges.
Other Emerging Viral Threats
Beyond these three, other viruses are also raising concerns. Chikungunya caused over 445,000 suspected and confirmed cases in 2025, with at least 155 deaths as of September, according to IFL Science. Brazil alone reported 129,000 cases and 121 deaths, according to the Ministry of Health’s arbovirus monitoring panel. The Nipah virus has also resurfaced following a recent outbreak in the Indian state of West Bengal, though experts currently believe it does not pose a pandemic threat. The Brazilian Ministry of Health has confirmed no cases within the country.
Resurgent diseases previously thought to be under control, such as measles, are also appearing due to declining vaccination rates, potentially jeopardizing eradication efforts in places like the United States. Some experts also caution that viruses like HIV could resurge if international health cooperation programs continue to be cut.
