Russia has seen a rise in ARVI and influenza cases over the past two weeks, with eight regions already exceeding epidemic thresholds. Most cases are still linked to non-influenza respiratory infections, but among flu viruses as much as 80% is now attributed to A(H3N2), the strain known as Hong Kong flu. Specialists expect it to remain dominant. A similar pattern is being reported in other countries, including England, Canada and Japan.
Doctors are paying particular attention to this variant because of its high transmissibility and its tendency to cause more severe illness. The first H3N2 outbreak was recorded in 1968 in Hong Kong. The virus then spread rapidly across several continents, and the pandemic, which lasted two years, is estimated to have caused up to 4 million deaths. It was after that outbreak that the World Health Organization began updating the antigenic composition of flu vaccines every year.
The symptoms of H3N2 are generally typical of influenza: a sudden high fever, headache, muscle aches, dry cough, sore throat and nasal congestion. Specialists note, however, that influenza A usually runs a more severe course than influenza B and more often leads to complications, including pneumonia and damage to the respiratory tract and nervous system. Another feature of H3N2 is its short incubation period, which allows the illness to progress quickly.
For the 2025/2026 season, vaccine formulations included A(H1N1), A(H3N2) and influenza B strains. But according to Ancha Baranova, a professor at George Mason University’s School of Systems Biology, H3N2 acquired seven new mutations over the summer and became better at evading immune responses. She said a separate branch now dominates the season and is identified as the “K lineage.”
“The vaccine was not a perfect match, but we still have nothing better. It still provides cross-protection and strengthens the immune response,” a Russian infectious disease specialist told the publication on condition of anonymity.
St. Petersburg’s Pasteur Research Institute of Epidemiology and Microbiology said early data showed vaccinated people had protective antibody levels capable of neutralizing the circulating A(H3N2) strain by 80–90%. Foreign experts are more cautious. Baranova said a British study found that neutralizing the mutated virus required eight times more antibodies than are typically produced after vaccination against the older version of the strain.
Specialists are not offering precise forecasts for the season. Some expect a moderate epidemic period, while others warn that winter may be difficult, citing Australia’s severe season. In Russia, flu incidence usually peaks in December and January. Experts advise those who were not vaccinated to use familiar precautions from the coronavirus pandemic: wear a mask in crowded places, wash hands frequently, disinfect gadgets and stay home when sick.