For a study, it was determined that there was no proof that influenza vaccination programs regularly protect unvaccinated individuals in a community (i.e., indirect effects). In the Household Influenza Vaccine Evaluation (HIVE) cohort, the researchers wanted to know the influenza vaccine’s direct, indirect, and overall impact. Using adjusted mixed-effect Poisson regression models, the researchers calculated direct, indirect, and total influenza vaccine efficacy (VE) and the incidence rate ratio of influenza virus infection using longitudinal data from the HIVE cohort from 2010–11 to 2017–18. Vaccinated members of fully or partially vaccinated homes were compared to unvaccinated persons in completely unvaccinated households to establish total effectiveness. The total VE against any influenza strain was 30.2% (14.0–43.4). Direct VE was higher for influenza A/H1N1 43.9% (3.9 to 63.5) and B 46.7% (17.2 to 57.5) than for influenza A/H3N2 31.7% (10.5 to 47.8) and for small children 42.4% (10.1 to 63.0) than for adults 18.6% (6.3 to 37.7). Incomplete unvaccinated households had the highest influenza incidence (10.6 per 100 person-seasons), while all other categories of household vaccination coverage had the lowest. After correcting for various confounders, the researchers observed little evidence of indirect VE. Low coverage had 56.4% (30.1–72.9) VE, moderate coverage had 43.2% (19.5–59.9) VE, and fully vaccinated households had 33.0% (12.1–49.0) VE. Influenza vaccines may provide benefits in addition to the direct effect; however, the effect was minimal in the trial. Exceptions notwithstanding, the purpose of global vaccine recommendations should remain the provision of verifiable, direct protection to those who have been vaccinated.
Has Influenza Vaccine Efficacy Been Demonstrated in the HIVE Household Cohort Over 8 Years? Is There Evidence of Indirect Protection?
