Journal of medical virology
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Randomized Controlled Trial Multicenter Study
Benefits of increasing the dose of influenza vaccine in residents of long-term care facilities: a randomized placebo-controlled trial.
Increased vaccine doses and mid-season boosting may increase the proportion of residents with protective immunity from influenza in long-term care facilities. In a multi-center study (1997-1998), 815 residents from 14 long-term care facilities were assigned at random to receive 15 or 30 microg of inactivated influenza vaccine, followed by a 15 microg booster vaccine or a placebo vaccine at Day 84. Seroresponses were re-analyzed by hemagglutination-inhibition (> or =4-fold titer increases, protective titer > or =40, geometric mean titers. ⋯ Booster vaccination after an initial 15 microg dose of the vaccine did not increase the protective rate (61.9% vs. 63.9% after placebo). The number of participants needed to vaccinate to protect one additional resident by a dose of 15 microg was 4, by a dose of 30 microg 3, and 15 when using a 30 microg dose instead of 15 microg. Doubling the dose of influenza vaccine increased protection-related responses among residents of long-term care facilities, especially in those with low pre-vaccination titers.