(HealthDay News) — Vaccination for influenza for multiple seasons is twice as effective in preventing severe influenza — compared with non-severe influenza — in older patients admitted to hospital, according to a study published in CMAJ, the journal of the Canadian Medical Association.

Itziar Casado, MD, from the Instituto de Salud Pública de Navarra in Pamplona, Spain, and colleagues assessed the effectiveness of vaccination in preventing influenza among community-dwelling adults (≥65 years) who were admitted to 1 of 20 hospitals for laboratory-confirmed influenza (130 inpatients with severe influenza and 598 inpatients with non-severe influenza). Cases were matched with inpatient controls by sex, age, hospital, and admission date (333 and 1493 controls, respectively).

The researchers found that, compared with patients who were unvaccinated in the current and 3 previous seasons, adjusted effectiveness of influenza vaccination in the current and any previous season was 31% in preventing admission to hospital for non-severe influenza, 74% in preventing admissions to the intensive care unit, and 70% in preventing death. There was no significant effect on cases of severe influenza for vaccination in the current season only. There was a reduced risk of severe outcomes from influenza (adjusted odds ratio, 0.45) for vaccination in the current and any previous season.

“These results reinforce recommendations for annual vaccination for influenza in older adults,” the authors write.

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Casado I, Domínguez A, Toledo D, et al. Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case–control study. CMAJ January 08, 2018 190 (1) E3-E12. doi:10.1503/cmaj.170910