How effective are quadrivalent versus trivalent flu vaccines for the strains circulating in the UK this season?
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Executive summary
The UK has shifted its national programme from quadrivalent to trivalent influenza vaccines because WHO and EU/UK advisers judge B/Yamagata absent since March 2020; all vaccines marketed for 2025–26 in the UK are trivalent and JCVI prefers trivalent formulations where available [1] [2] [3]. Regulatory bodies and expert reviews say trivalent and quadrivalent vaccines from the same manufacturer show similar immunogenicity for the two A strains and the chosen B strain, and that removing B/Yamagata should not reduce protection against currently circulating strains [4] [5] [6].
1. Why the change happened — the disappearance of B/Yamagata
Global surveillance has not confirmed circulation of naturally occurring B/Yamagata lineage viruses since March 2020, prompting WHO, EMA and other experts to advise removing the B/Yamagata component; that recommendation underpins the move from quadrivalent to trivalent vaccines in the EU/UK for 2025–26 [6] [7] [1].
2. What’s happening in the UK programme now
UK authorities report that manufacturers have moved or are moving to trivalent formulations, JCVI prefers trivalent inactivated vaccines if available, and official lists show all vaccines marketed for 2025–26 in the UK are trivalent formulations [8] [3] [2]. UKHSA/Department of Health guidance and professional materials explicitly state that all inactivated vaccines used in the programme will be trivalent [1] [9].
3. How effectiveness compares on the key strains
Immunological and regulatory assessments indicate that, for the shared components (the two A strains and the selected B Victoria strain), trivalent and quadrivalent formulations from the same brand have shown equivalent responses; quadrivalent vaccines mainly added protection against the second B lineage rather than changing protection to the other three strains [5] [4]. Expert reviews conclude updated trivalent vaccines “contain all WHO-selected strains” and maintain vaccine effectiveness for the strains expected to circulate [4].
4. The residual risk: what could be missed by dropping the fourth strain
The principal loss when moving from quadrivalent to trivalent is absence of the B/Yamagata antigen — valuable only if B/Yamagata re-emerges. WHO and EMA judge re-emergence unlikely given no detections since 2020, but they and national bodies note transition should be managed carefully and that quadrivalent production can still be considered if supply issues require it [6] [7] [8]. Available sources do not quantify the small probability and potential impact of an unforeseen B/Yamagata comeback beyond statements of “very low risk” [6].
5. Cost, supply and programmatic rationales
Authorities cite manufacturing, supply resilience and cost considerations in the transition: trivalent vaccines are historically less complex and have been promoted after the WHO recommendation to exclude B/Yamagata, with EMA and WHO framing the move as preserving supply and programme value [6] [7] [1]. JCVI guidance instructs vaccinators to order the preferred (first-line) vaccines regardless of whether labels still say “quadrivalent” or “trivalent” as manufacturers convert production [8].
6. Competing viewpoints and uncertainties
Experts and regulators largely align on the decision, but literature and past analyses show the theoretical advantage of quadrivalent vaccines is protection against mismatch when the second B lineage circulates; that advantage disappears only if that lineage truly vanishes — a premise based on surveillance since 2020 [5] [6]. Some EU guidance allowed contingency for quadrivalent production “if unavoidable” to avoid hampering campaigns, indicating residual caution among regulators [7].
7. Practical takeaway for clinicians and the public
For the 2025–26 UK season, the trivalent vaccines in use are expected to protect against the two A strains and the B Victoria lineage chosen by WHO; JCVI and UK programme documents explicitly say trivalent formulations offer the same protection for those strains and should be used in preference where authorised [1] [3] [9]. If your concern is whether the switch materially reduces protection against currently circulating viruses, UK and international authorities and expert reviews affirm it should not [4] [1].
Limitations: these conclusions are drawn from regulatory statements, JCVI guidance and expert reviews supplied here; they rely on surveillance data that show no B/Yamagata detections since March 2020 and on immunogenicity comparisons between formulations [6] [5] [4]. Available sources do not provide quantified real‑world effectiveness comparisons for the 2025–26 UK season against clinical outcomes, nor do they present modelling of the consequences if B/Yamagata were to reappear.