Effectiveness of Influenza Vaccines in the HIVE Household Cohort Over 8 Years: Is There Evidence of Indirect Protection?

Abstract

Background The evidence that influenza vaccination programs regularly provide protection to unvaccinated individuals (ie, indirect effects) of a community is lacking. We sought to determine the direct, indirect, and total effects of influenza vaccine in the Household Influenza Vaccine Evaluation (HIVE) cohort. Methods Using longitudinal data from the HIVE cohort from 2010–11 through 2017–18, we estimated direct, indirect, and total influenza vaccine effectiveness (VE) and the incidence rate ratio of influenza virus infection using adjusted mixed-effect Poisson regression models. Total effectiveness was determined through comparison of vaccinated members of full or partially vaccinated households to unvaccinated individuals in completely unvaccinated households. Results The pooled, direct VE against any influenza 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 A/H3N2 31.7% (10.5 to 47.8) and was higher for young children 42.4% (10.1 to 63.0) than adults 18.6% (−6.3 to 37.7). Influenza incidence was highest in completely unvaccinated households (10.6 per 100 person-seasons) and lower at all other levels of household vaccination coverage. We found little evidence of indirect VE after adjusting for potential confounders. Total VE was 56.4% (30.1–72.9) in low coverage, 43.2% (19.5–59.9) in moderate coverage, and 33.0% (12.1 to 49.0) in fully vaccinated households. Conclusions Influenza vaccines may have a benefit above and beyond the direct effect but that effect in this study was small. Although there may be exceptions, the goal of global vaccine recommendations should remain focused on provision of documented, direct protection to those vaccinated.

Children’s role in the COVID-19 pandemic: a systematic review of early surveillance data on susceptibility, severity, and transmissibility

“…A recent meta-analysis estimating secondary attack rates by age of the index case and their contact found no significant difference by age in transmissibility. When this was limited to household studies there was weak but not statistically significant evidence that children were less transmissible than adults 123 .…”

“…This agrees with a recent meta-analysis that included non-peer reviewed studies, which also estimated a lower susceptibility to infection in children and adolescents with a pooled odds ratio of 0.56 (95% CI: 0.37–0.85) 121 , 122 .Similarly a study carried out using household data in Bnei Brak in Israel found that children were less susceptible to SARS-CoV-2 infection that adults Other meta-analyses investigating data on the age of index cases and their contacts found no significant difference in susceptibility by age. However, when this was limited to household settings only, Thompson et al found that adults were statistically significantly more susceptible to SARS-CoV-2 infection compared to children 123 . Jing et al found similar age-dependent susceptibility in household settings 124 .…”

Respiratory Virus Circulation during the First Year of the COVID-19 Pandemic in the Household Influenza Vaccine Evaluation (HIVE) Cohort

“…Many of the non-pharmaceutical interventions deployed worldwide at the beginning of the COVID-19 pandemic were originally developed as a strategy for early reduction of peak transmission levels during an influenza pandemic, so the reduction in the circulation of many non-SARS-CoV-2 respiratory viruses was concurrent to the adoption of mitigation and continued high levels of influenza vaccination in the study participants was not surprising. [15][16][17][18] However, as influenza pandemics pass through communities in a matter of months, the maintenance of these measures over longer periods during multiple waves of COVID-19 may have disrupted the seasonality of other respiratory viruses to a degree never before seen. [19][20][21][22] The mechanism for the disruption of seasonal respiratory viruses by SARS-CoV-2 circulation-whether via non-pharmaceutical mitigation or an interference effect-remains unclear.…”

Respiratory virus circulation during the first year of the COVID‐19 pandemic in the Household Influenza Vaccine Evaluation (HIVE) cohort

“…wide at the beginning of the COVID-19 pandemic were originally developed as a strategy for early reduction of peak transmission levels during an influenza pandemic, so the reduction in the circulation of many non-SARS-CoV-2 respiratory viruses was concurrent to the adoption of mitigation and continued high levels of influenza vaccination in the study participants was not surprising. [15][16][17][18] However, as influenza pandemics pass through communities in a matter of months, the maintenance of these measures over longer periods during multiple waves of COVID-19 may have disrupted the seasonality of other respiratory viruses to a degree never before seen. [19][20][21][22] The mechanism for the disruption of seasonal respiratory viruses by SARS-CoV-2 circulation-whether via non-pharmaceutical mitigation or an interference effect-remains unclear.…”