Influenza Vaccine Uptake in the Year After Concurrent vs Separate Influenza and Zoster Immunization

IMPORTANCE: Fewer than half of US adults receive the influenza vaccine each year; many cite concerns about side effects, which occur infrequently. By contrast, the recombinant zoster vaccine causes systemic side effects in a large proportion of patients. OBJECTIVE: To determine whether concurrent administration of the influenza and zoster vaccines was associated with a reduced likelihood of influenza vaccination in the subsequent year. DESIGN, SETTING, AND PARTICIPANTS: This cohort study included patients aged 50 years or older who received the influenza vaccine between August 1, 2018, and March 31, 2019, and received the zoster vaccine on the same day or separately (within the prior 180 days). Data were gathered from a national claims database of patients with commercial insurance and Medicare Advantage plans. Logistic regression analysis was used to adjust for baseline demographic characteristics, comorbidities, influenza vaccine month and location (pharmacy vs medical office), and health care use (including influenza vaccination in the prior year). EXPOSURES: Concurrent vs separate influenza and zoster vaccine administration. MAIN OUTCOMES AND MEASURES: Receipt of the influenza vaccine in the subsequent year (August 1, 2019, to March 31, 2020). RESULTS: Among 89 237 individuals included in this study, the median age was 72 years (IQR, 67-77 years), 58.3% were women, 70.1% were White, and 85.7% had at least 1 comorbidity. Influenza vaccine uptake in 2019-2020 was lower among 27 161 individuals who received concurrent influenza and zoster vaccines compared with the 62 076 individuals who received the vaccines on separate days (87.3% vs 91.3%; adjusted odds ratio, 0.74; 95% CI, 0.71-0.78; P < .001). Results were similar across subgroups. CONCLUSIONS AND RELEVANCE: Results of this cohort study suggest that concurrent administration of influenza and zoster vaccines was associated with a reduction in receipt of the influenza vaccine the following year. One possible explanation is that some patients could have misattributed systemic side effects caused by the zoster vaccine to the influenza vaccine. It may be preferable to administer these 2 vaccines separately or enhance patient counseling about expected vaccine side effects.