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Comparisons of LAIV and TIV Efficacy Both TIV and LAIV have been demonstrated to be effective in children and adults, but data directly comparing the efficacy or effectiveness of these two types of influenza vaccines are limited. Studies comparing the efficacy of TIV to that of LAIV have been conducted in a variety of settings and populations using several different clinical endpoints. One randomized, double-blind, placebo-controlled challenge study among 92 healthy adults aged 18-41 years assessed the efficacy of both LAIV and TIV in preventing influenza infection when challenged with wild-type strains that were antigenically similar to vaccine strains (249). The overall efficacy in preventing laboratory-documented influenza from all three influenza strains combined was 85% and 71%, respectively, when challenged 28 days after vaccination by viruses to which study participants were susceptible before vaccination. The difference in efficacy between the two vaccines was not statistically significant in this limited study, but efficacy at timepoints later than 28 days after vaccination was not determined. In a randomized, double-blind, placebo-controlled trial, conducted among young adults during an influenza season when the majority of circulating H3N2 viruses were antigenically drifted from that season's vaccine viruses, the efficacy of LAIV and TIV against culture-confirmed influenza was 57% and 77%, respectively. The difference in efficacy was not statistically significant and was based largely upon a difference in efficacy against influenza B (135). Although LAIV is not currently licensed for use in children aged <5 years or in persons with risk factors for influenza complications, several studies have compared the efficacy of LAIV to TIV in these groups. LAIV provided 32% increased protection in preventing culture-confirmed influenza compared with TIV in one study conducted among children aged >6 years and adolescents with asthma (245) and 52% increased protection among children aged 6-71 months with recurrent respiratory tract infections (245). Another study conducted among children aged 6-71 months during 2004-2005 demonstrated a 55% reduction in cases of culture-confirmed influenza among children who received LAIV compared with those who received TIV (242). |