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the claim
The flu vaccine is updated every year because flu viruses are constantly changing.
the verdict
SUPPORTED
the evidence backs this
Recorded sources
6 sources for · 0 against
Is it true that the flu vaccine is updated every year because flu viruses are constantly changing?
Yes. The annual updating of the flu vaccine is necessary because circulating influenza viruses undergo continuous antigenic drift and rapid genetic evolution.
Verdict: SUPPORTED · 6 sources for, 0 against · Last checked
The analysis
The retrieved papers consistently confirm that influenza viruses evolve rapidly via antigenic drift, which requires annual reformulation and updates of seasonal flu vaccines to maintain efficacy.
Evidence for · 6
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F, B., N, P., G, C., F, S., M, G., & M, C. (2026). Influenza A(H3N2) Subclade K (J.2.4.1): Molecular Characterization, Antigenic Divergence, and Global Spread During the 2025/26 Season.. doi.org. https://doi.org/10.3390/idr18020037
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More for · 5
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R, H., C, W., AM, B., D, G., P, S., M, G., D, B., YW, C., J, B., H, W., H, W., KE, B., A, J., A, A., G, A., E, F., EL, V., A, R., O, H., K, B., C, S., B, W., S, G., S, G., EJ, C., NS, L., EC, W., & MY, W. (2026). Assessment of human immunity to A/H3N2 influenza subclade K during 2025 emergence.. doi.org. https://doi.org/10.1016/j.ebiom.2026.106332
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RK, G., KR, A., & JL, C. (2026). Low effectiveness of influenza vaccines vis-à-vis mechanism of protection by vaccines - potential causes and recommendations to improve control of influenza.. doi.org. https://doi.org/10.3389/fimmu.2026.1816148
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MV, S., P, K., Y, D., E, R., V, K., J, B., MA, S., I, K., & D, L. (2026). Duration of the Humoral Immune Response to Influenza Vaccination in a Cohort of Repeatedly Vaccinated Adults over Four Consecutive Epidemic Seasons: 2018/19-2021/22 Observational Study.. doi.org. https://doi.org/10.3390/vaccines14090800
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Y, A., M, C., C, Z., M, Z., X, W., W, H., X, Z., & Y, W. (2026). Consensus H3N2 HA immunogens incorporating key antigenic mutations elicit broad-spectrum neutralizing responses.. doi.org. https://doi.org/10.1080/22221751.2026.2731497
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Pan, Y. & Deem, M. W. (2016). Prediction of Influenza B Vaccine Effectiveness from Sequence Data. arxiv.org. https://doi.org/10.1016/j.vaccine.2016.07.015
What does the evidence say?
The retrieved papers consistently confirm that influenza viruses evolve rapidly via antigenic drift, which requires annual reformulation and updates of seasonal flu vaccines to maintain efficacy.
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