Czy mutacje A(H3N2) w 2025 roku wpływają na konieczność aktualizacji szczepionki?
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Executive summary
Mutations that created A(H3N2) “subclade K” (also called J.2.4.1) emerged after the 2025 vaccine strains were selected and show reduced lab reactivity to the vaccine reference viruses, prompting concern about mismatch; WHO and UK data nonetheless report that current vaccines still protect against severe outcomes, with UKHSA estimating 70–75% effectiveness against hospital attendance in children and 30–40% in adults [1] [2] [3] [4]. Available sources do not state that regulators have recommended an immediate reformulation of the 2025–26 vaccines [3] [5].
1. What changed in A(H3N2) and when it happened
Genetic surveillance detected a rapidly spreading H3N2 branch called subclade K (J.2.4.1) beginning around June–August 2025; the variant carries a set of HA mutations (including T135K and K189R plus others) that distinguish it from the J and J.2 viruses used when vaccine strains were chosen earlier in 2025 [6] [2] [3].
2. Laboratory signals: reduced reactivity, not automatic obsolescence
Ferret antisera and human serology testing showed reduced antigenic reactivity of subclade K viruses to the NH 2025/26 vaccine reference strains and to post-infection ferret antisera raised against vaccine strains, a laboratory sign of antigenic drift that can lower vaccine match [2] [7] [5]. Reduced lab reactivity raises the need for close monitoring but is not by itself a regulatory instruction to change vaccine composition [7] [5].
3. Real-world effectiveness: evidence that vaccines still prevent severe outcomes
Despite antigenic drift signals, surveillance and early effectiveness data indicate the 2025–26 vaccines continue to confer important protection: WHO and UK sources say vaccines are still expected to protect against severe illness, and UKHSA early estimates report 70–75% effectiveness against hospital attendance in children and 30–40% in adults [3] [4] [2]. Public-health agencies therefore continue to recommend vaccination to reduce severe disease and hospital burden [3] [4].
4. Why a lab mismatch does not always mean immediate reformulation
Vaccine strain selection follows a global timetable; vaccines for the Northern Hemisphere 2025–26 season were chosen before subclade K’s rise, so the emergence after selection explains the mismatch timing [6] [1]. WHO, the ECDC and national authorities use a combination of genetic, antigenic (lab) and real-world epidemiological data to decide on future composition — not a single mutation — which is why sources note monitoring and analysis rather than emergency reformulation recommendations [5] [7] [3].
5. Where authorities stand and what they’re asking of surveillance systems
WHO and EU/EEA guidance emphasize sustained surveillance and prompt sharing of sequences and epidemiologic data (EpiPulse, GISAID) so vaccine composition meetings can assess whether future updates are warranted; ECDC’s technical notes and WHO reports highlight subclade K’s divergence and call for continued reporting, not an immediate overhaul of existing deployed vaccines [5] [7] [3].
6. Competing perspectives in the coverage
Scientists and reporters emphasize two competing facts: lab assays show reduced reactivity (a signal of drift) while early real-world data show vaccines still preventing severe outcomes [2] [4]. Outlets such as CT Mirror and STAT stress the timing problem—K emerged after vaccine selection—and note continued benefit from vaccination [1] [6]. Gavi and public agencies stress that lab measures are only part of the story and that vaccination remains protective [8] [3].
7. Practical advice implied by the evidence
Given the documented antigenic changes yet retained protection against severe disease, public-health agencies cited in current reporting continue to recommend vaccination to reduce hospitalization and death, while urging continued surveillance to inform next season’s vaccine composition [3] [4] [2]. Available sources do not mention new emergency booster campaigns or an official call to replace 2025–26 vaccine lots mid-season [3] [5].
8. Limitations and open questions
Existing reporting documents reduced lab reactivity and early VE estimates but notes limited real-world effectiveness data overall for the 2025–26 vaccines; it remains uncertain how clinical disease protection will evolve across locales and age groups as the season progresses [5] [2]. Decisions about reformulating vaccines for future seasons will rely on ongoing virological, serological and VE studies that sources say are still underway [7] [3].
Bottom line: the mutations that define A(H3N2) subclade K created a measurable antigenic drift after the 2025 vaccine strains were fixed, prompting concern and intensified surveillance, but current international reporting and early real-world data indicate the present vaccines still reduce severe outcomes — so authorities are monitoring and collecting more VE data rather than ordering an immediate change to the 2025–26 vaccine formulation [6] [2] [3] [4].