Vaccine

Background

There have been inconsistent reports of decreased vaccine effectiveness (VE) against influenza viruses among older adults (aged ≥65 years) compared with younger adults in the United States. A direct comparison of VE over multiple seasons is needed to assess the consistency of these observations.

Methods

We performed a pooled analysis of VE over 5 seasons among adults aged ≥18 years who were systematically enrolled in the U.S. Flu VE Network. Outpatients with medically-attended acute respiratory illness (cough with illness onset ≤7 days prior to enrollment) were tested for influenza by reverse transcription polymerase chain reaction. We compared differences in VE and vaccine failures among older adult age group (65–74, ≥75, and ≥65 years) to adults aged 18–49 years by influenza type and subtype using interaction terms to test for statistical significance and stratified by prior season vaccination status.

Results

Analysis included 20,022 adults aged ≥18 years enrolled during the 2011–12 through 2015–16 influenza seasons; 4,785 (24%) tested positive for influenza. VE among patients aged ≥65 years was not significantly lower than VE among patients aged 18–49 years against any subtype with no significant interaction of age and vaccination. VE against A(H3N2) viruses was 14% (95% confidence interval [CI]−14% to 36%) for adults ≥65 years and 21% (CI 9%-32%) for adults 18–49 years. VE against A(H1N1)pdm09 was 49% (95% CI 22%-66%) for adults ≥65 years and 48% (95% CI 41%-54%) for adults 18–49 years and against B viruses was 62% (95% CI 44%–74%) for adults ≥65 years and 55% (95% CI 45%-63%) for adults 18–49 years. There was no significant interaction of age and vaccination for separate strata of prior vaccination status.

Conclusions

Over 5 seasons, influenza vaccination provided similar levels of protection among older and younger adults, with lower levels of protection against influenza A(H3N2) in all ages.

29402578

PMC5812289

Journal Article

CDC Public Access