There isn’t just one “new virus” making headlines right now. Several emerging viral threats have gained attention in 2024 and 2025, each posing different levels of risk. The ones generating the most concern are H5N1 bird flu spreading through U.S. livestock, a more dangerous strain of mpox circulating in Africa, and lesser-known viruses like Oropouche and Chandipura causing outbreaks in specific regions. Here’s what you need to know about each.
H5N1 Bird Flu in Humans
H5N1 avian influenza has been the most widely covered emerging virus in the U.S. over the past year. The virus has circulated in wild birds for decades, but recent outbreaks in dairy cows and poultry brought it into closer contact with people. As of December 31, 2024, the CDC had identified 66 human cases of H5 bird flu in the United States, nearly all linked to direct exposure to infected animals.
The risk to the general public remains low. The people getting infected are overwhelmingly farmworkers and others who handle infected poultry, dairy cows, or raw milk without adequate protective equipment. The CDC has monitored more than 10,600 people following animal exposures and tested over 540 of them. There is no evidence of sustained person-to-person spread, which is the threshold that would signal a broader public health emergency.
The concern with H5N1 isn’t what it’s doing now. It’s what it could do. Influenza viruses mutate rapidly, and every human infection gives the virus another opportunity to adapt to human cells. If H5N1 gained the ability to spread easily between people, it could trigger a pandemic. Health agencies are stockpiling vaccines and closely tracking genetic changes in the virus for exactly this reason.
Mpox Clade Ib
Mpox (formerly monkeypox) returned to global attention in 2024 with the emergence of Clade Ib, a strain first identified in Central and East Africa. This strain prompted the WHO to declare a public health emergency of international concern in August 2024. Unlike the Clade IIb strain that spread globally in 2022, Clade Ib was initially thought to carry a higher fatality rate, though real-world data has been more reassuring in some settings.
In Kenya, where 48 confirmed Clade Ib cases were tracked between July 2024 and February 2025, 47 patients recovered and one died. That single death occurred in a patient with advanced, untreated HIV and other serious infections. Sexual contact was the suspected transmission route in about 63% of cases, with the outbreak concentrated among truck drivers, sex workers, and people in surrounding communities. Close household contact accounted for a smaller share of cases.
A two-dose vaccine called Jynneos is available and effective. Studies from the UK estimated it at roughly 80% effective at preventing infection. Among vaccinated people who did get mpox, none required hospitalization, while unvaccinated patients made up the vast majority of those needing hospital care.
Oropouche Virus (Sloth Fever)
Oropouche virus grabbed attention in 2024 after a major outbreak in Brazil, where more than 8,000 cases were reported between January and August. The virus, sometimes called “sloth fever,” is spread by biting midges and possibly certain mosquitoes. It had been known for decades in South America but had never caused an outbreak this large or this severe.
Symptoms look a lot like dengue or Zika: sudden fever, chills, headache, muscle and joint pain, and sometimes eye pain, light sensitivity, nausea, vomiting, or rash. Most people recover, but two previously healthy women died during the 2024 outbreak, marking the first known fatalities from the virus.
More alarming was the discovery that the virus can pass from a pregnant person to the fetus. Brazil reported five cases of vertical transmission associated with fetal death or congenital abnormalities, including microcephaly, a condition where a baby’s head is abnormally small. This was the first time such complications had been documented with Oropouche, drawing immediate comparisons to the Zika crisis of 2015-2016. There is currently no vaccine or specific treatment.
Chandipura Virus in India
Chandipura virus caused an outbreak in India in mid-2024 that was especially deadly among children. Between early June and mid-August, India reported 245 cases of acute encephalitis syndrome linked to the virus, with 82 deaths, a fatality rate of 33%. The virus primarily affects children under 15, starting with a fever that can rapidly progress to seizures, coma, and death.
The case fatality rate from Chandipura infection historically ranges from 56% to 75%, and there is no specific treatment or vaccine. The virus is spread by sandflies, making it a regional threat in parts of South Asia. While it poses little risk outside these areas, its lethality in children makes it one of the most dangerous viruses on the current global radar.
Borealpox (Formerly Alaskapox)
A much smaller but novel threat emerged from Alaska. Borealpox, originally called Alaskapox, is a newly identified virus in the same family as smallpox and mpox. Only six human cases have ever been reported, all in Alaska. Symptoms include one or more skin bumps or pustules, swollen lymph nodes, and joint or muscle pain.
The virus appears to circulate in small mammals, particularly red-backed voles and shrews. Domestic cats and dogs may also play a role in spreading it to humans. One immunocompromised patient died from the infection in early 2024, making it the first known fatality. For most people, the risk is extremely low, but the discovery of an entirely new poxvirus in North America underscored how many unknown pathogens still exist in animal populations.
What “Disease X” Means
You may have also seen the term “Disease X” in headlines. This isn’t an actual virus. It’s a placeholder concept used by the WHO and global health organizations to represent the next pandemic pathogen, one that hasn’t been identified yet. The idea is to encourage governments and researchers to build flexible preparedness systems (rapid vaccine platforms, surveillance networks, stockpiled supplies) that can respond to any new threat, not just the ones we already know about.
Organizations like CEPI maintain priority pathogen lists that include known threats such as Ebola, Nipah, Lassa fever, and Rift Valley fever alongside Disease X. The goal is to fund research into these viruses before they cause large outbreaks, rather than scrambling to respond after the fact.
How These Viruses Compare
- Highest immediate risk globally: H5N1, because of its pandemic potential if it adapts to human-to-human spread.
- Most active outbreaks: Mpox Clade Ib in Africa and Oropouche in South America both caused thousands of cases in 2024.
- Most lethal per case: Chandipura virus, with fatality rates above 50% in confirmed infections, predominantly in children.
- Most novel: Borealpox, an entirely new virus with only six known human cases.
- Vaccine available: Only mpox (Jynneos, roughly 80% effective). H5N1 vaccines exist in stockpile but are not widely distributed. No vaccines exist for Oropouche, Chandipura, or borealpox.
For most people outside of outbreak zones or high-risk occupations, the day-to-day risk from these viruses remains low. The reason they make news is their potential to change quickly, whether through mutation, geographic spread, or a jump into new animal or human populations.