Which virus could cause the next pandemic after COVID-19?

The COVID-19 pandemic is over, but scientists warn that another global outbreak is not a question of “if” but “when.” The WHO states a new pandemic could arrive “in 20 years or tomorrow,” while analysts at Airfinity have estimated the probability of encountering a major new virus within the next ten years at roughly 27.5%. Russian Academy of Sciences epidemiologist Gennady Onishchenko has offered a more specific — though personal — forecast, suggesting a new crisis could emerge around 2035–2036. None of these figures amount to a confirmed timetable; viral mutations are inherently unpredictable.

The next pandemic could arrive very suddenly

How a new pandemic could begin

For a genuine global threat to materialize, several conditions must align simultaneously:

• A pathogen must jump from an animal host into a human;
• The virus must acquire the ability to spread easily between people;
• The general population must lack pre-existing immunity;
• Public-health systems must fail to contain the initial outbreak.

Many dangerous infections have existed for years without ever reaching the stage of global spread. Based on historical patterns, the most probable window of elevated risk falls in the late 2020s through the mid-2030s — but this is a statistical observation, not a prediction. The WHO emphasizes that while new pandemics are inevitable, pinpointing their exact timing or geographic origin is impossible.

Influenza A: the historically dominant threat

When researchers model the next pandemic, influenza A is typically the first candidate. It was responsible for the global outbreaks of 1918, 1957, 1968, and 2009, and its chief weapon is extraordinary genetic variability.

A particularly dangerous scenario involves reassortment — the mixing of different influenza strains inside a single host organism. Pigs are often described as ideal “mixing vessels” because their cells can be simultaneously infected by both avian and human flu viruses. A plausible chain of events:

1. An animal is co-infected with a bird flu virus and a human flu virus;
2. Genetic material is exchanged inside the animal’s cells;
3. A new hybrid strain emerges and infects a farm worker;
4. After further random mutations, the infection begins transmitting easily between people.

Although avian influenza H5N1 has attracted significant attention, the WHO currently assesses the risk to the general public as low. The virus has not yet acquired the ability to transmit stably from person to person; nearly all confirmed human cases have involved direct contact with infected birds. For H5N1 to become a global threat, it would need to gain new properties enabling it to efficiently enter human respiratory-tract cells.

What is “Disease X”?

Headlines about a terrifying “Disease X” circulate regularly on social media, but the term is not a secret bioweapon or a hidden laboratory virus. It is a placeholder designation coined by the WHO to represent an as-yet-unknown pathogen that could potentially trigger an international epidemic. The purpose is to ensure that medical preparedness extends beyond known threats.

In 2024, experts analyzed more than 1,600 different microorganisms to assess where the next danger might originate. “Disease X” could ultimately turn out to be an unknown strain of the Nipah virus, an antibiotic-resistant bacterium, or an entirely new family of infections.

Coronaviruses also remain under close surveillance. Some scientists note that the emergence of a new coronavirus from an animal reservoir is one of the most realistic scenarios. Viruses related to SARS and MERS have large genomes, mutate readily, and periodically cross the species barrier.

Scientists are analyzing thousands of viruses to prepare in advance for unknown threats

Why pandemic risk is growing

The world has not become inherently more fragile, but human behavior has changed in ways that increase exposure. WHO statistics indicate that more than 60% of new infectious diseases originate in animals — and the chances of such cross-species encounters are rising.

Deforestation and the expansion of farming push wildlife into closer contact with humans and livestock. On large-scale industrial farms, thousands of genetically similar animals are housed together; if an infection enters such a facility, it gains an ideal testing ground for mutations.

Globalization amplifies the speed of spread. In earlier eras, a person carrying a dangerous disease might never have traveled far from their village. Today, an infected passenger can cross a continent in hours, distributing a virus through international airports before the first symptoms appear. Climate change adds another dimension: warming temperatures are expanding the habitats of ticks and mosquitoes, carrying tropical fevers into previously unaffected regions.

How prepared is the world?

The early phase of a future pandemic would likely resemble the beginning of COVID-19 — localized reports of unusual pneumonia, debates over transmissibility, and a lack of reliable diagnostic tests. However, this does not necessarily mean a repeat of the strict lockdowns of 2020. The response would depend on the specific virus’s severity, speed of transmission, and susceptibility to basic countermeasures such as masks.

Despite alarming forecasts, the world is significantly better equipped than it was a few years ago. Scientists can now sequence the genome of an unknown pathogen within days, and modern vaccine platforms can produce candidates in record time. The priority should not be trying to guess the exact year of the next crisis, but rather strengthening laboratory networks and global public-health infrastructure to break chains of transmission before they paralyze the planet.