The emergence of the new subclade K variant of the H3N2 flu virus has raised concerns among experts as they prepare for the 2025-2026 flu season. This new variant, which started spreading in June and July, has genetic changes that could make people more susceptible to getting sick and may reduce the effectiveness of this year’s flu vaccine.
Influenza experts are closely monitoring the situation as flu activity in North America begins to increase. The mutations in the H3N2 virus suggest that the antibodies people have developed may not be as effective against the new subclade K variant. This could lead to a higher burden of flu cases this season, despite vaccination efforts.
While there is concern about the potential impact of the subclade K variant, experts stress the importance of getting a flu shot this year. The flu vaccine still offers protection against other strains of the flu, including H1N1 and flu B. Studies from previous seasons with vaccine mismatches have shown that the flu shot can still provide some level of protection against severe illness requiring hospitalization.
Experts like Scott Hensley and Kanta Subbarao emphasize that even if the vaccine does not prevent infection with the subclade K variant, it can still reduce the severity of illness in those who do get sick. This was seen in the 2014-2015 season, which had a similar vaccine mismatch but still provided some protection against severe illness.
Arnold Monto and Florian Krammer are optimistic that residual immunity from last year’s strong H3N2 season may provide some level of protection against the new variant. However, scientists are closely monitoring the situation as the subclade K variant becomes dominant in countries like the United Kingdom and Japan.
Early studies in the UK have shown promising levels of protection from this year’s flu vaccine against the subclade K variant. However, experts like Danuta Skowronski remain cautious and believe that close monitoring of the situation is necessary as the flu season progresses.
The CDC’s first flu report for the season indicates that flu activity is still low in the United States, but a significant percentage of the viruses analyzed so far are H3N2 strains, with half of them being the subclade K variant. As the winter continues, experts will continue to assess the effectiveness of the flu vaccine against this new threat. The effectiveness of this season’s flu vaccine is still uncertain, as experts are waiting for more data to determine how well it will protect against the circulating viruses. According to Hensley, there is a possibility that the new viruses may have the ability to evade the immunity provided by the flu shot. His lab is currently conducting studies to analyze the antibodies in blood samples from vaccinated individuals and their ability to recognize the subclade K viruses. Results from these studies are expected in the coming weeks.
Australia has already experienced the impact of these viruses, with a flu season that extended beyond its usual timeframe due to the circulation of subclade K viruses. Ian Barr from the World Health Organization’s Collaborating Centre for Reference and Research on Influenza in Melbourne reported a significant number of laboratory-confirmed cases in the country, with a higher count compared to previous years.
Despite the increase in cases, Barr mentioned that there have been no alarming signs indicating that the subclade K viruses are causing more severe illness. The Melbourne collaborating center is closely monitoring the situation to gather more data on the impact of these viruses.
As for the upcoming flu season in North America, experts caution against making predictions, as forecasting flu activity is a challenging task. Subbarao emphasized the unpredictability of flu seasons and refrained from making any forecasts. The focus remains on gathering data and monitoring the situation to provide accurate assessments of flu activity.
In conclusion, the jury is still out on the effectiveness of the flu vaccine for this season, and experts stress the importance of obtaining valid estimates to assess the level of protection provided by the vaccine. Continuous monitoring and research are essential to understand the impact of the circulating viruses and make informed decisions regarding public health measures.
