• Iván Martínez-Baz, Ana Navascués, Itziar Casado, María Eugenia Portillo, Marcela Guevara, Carlos Gómez-Ibáñez, Cristina Burgui, Carmen Ezpeleta, and Jesús Castilla.
• Instituto de Salud Pública de Navarra - IdiSNA (Martínez-Baz, Casado, Guevara, Gómez-Ibáñez, Burgui, Castilla); Servicio de Microbiología Clínica, Complejo Hospitalario de Navarra - IdiSNA (Navascués, Portillo, Ezpeleta), Pamplona, Spain; CIBER Epidemiología y Salud Pública, (Martínez-Baz, Casado, Guevara, Burgui, Castilla) Madrid, Spain.
• CMAJ. 2021 Jul 26; 193 (29): E1120-E1128.

BackgroundAlthough annual influenza vaccination is recommended for persons with asthma, its effectiveness in this patient population is not well described. We evaluated the effect of influenza vaccination in the current and previous seasons in preventing influenza among people with asthma.MethodsUsing population health data from the Navarre region of Spain for the 2015/16 to 2019/20 influenza seasons, we conducted a test-negative case-control study to assess the effect of influenza vaccination in the current and 5 previous seasons. From patients presenting to hospitals and primary health care centres with influenza-like illness who underwent testing for influenza, we estimated the effects of influenza vaccination among patients with asthma overall and between those presenting as inpatients or outpatients, as well as between patients with and without asthma.ResultsOf 1032 patients who had asthma and were tested, we confirmed that 421 had influenza and the remaining 611 were test-negative controls. We found that the average effect of influenza vaccination was 43% (adjusted odds ratio [OR] 0.57, 95% confidence interval [CI] 0.40 to 0.80) for current-season vaccination regardless of previous doses, and 38% (adjusted OR 0.62, 95% CI 0.39 to 0.96) for vaccination in previous seasons only. Effects were similar for outpatients and inpatients. Among patients with asthma and confirmed influenza, current-season vaccination did not reduce the odds of hospital admission (adjusted OR 1.05, 95% CI 0.51 to 2.18). Influenza vaccination effects were similar for patients with and without asthma.InterpretationWe estimated that, on average, current or previous influenza vaccination of people with asthma prevented almost half of influenza cases. These results support recommendations that people with asthma receive influenza vaccination.© 2021 CMA Joule Inc. or its licensors.

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