Remaining Effect of Influenza Vaccines Received in Prior Seasons.

Martínez-Baz, Iván; Navascués, Ana; Casado, Itziar; Aguinaga, Aitziber; Ezpeleta, Carmen; Castilla, Jesús · J Infect Dis · 2019

prospective_cohort · Level II

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Abstract

This study evaluates the remaining effect of influenza vaccines received in the 5 prior seasons. During 7 influenza seasons, 8933 patients were enrolled and 47% were confirmed for influenza. Compared with unvaccinated individuals in the current and 5 prior seasons, vaccination was protective when the last dose had been received in the current season (40% [95% confidence interval {CI}, 32%-47%]), and 1 (42% [95% CI, 27%-54%]), 2-3 (35% [95% CI, 16%-49%]), or 4-5 seasons (31% [95% CI, 4%-51%]) prior. This effect lasted for fewer seasons in the elderly and in patients with chronic conditions. On average, several recent prior doses were as protective as current-season vaccination.

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