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If immunisation is too low, dropping temperatures in fall 2021 may lead to epidemic resurgence – as in 1918, 1957 and 2020. Swiss Med Wkly [Internet]. 2021 Aug. 18 [cited 2025 Oct. 14];151(3334):w30014. Available from:
https://www.smw.ch/index.php/smw/article/view/3052