Medication count, including statin or metformin use, is not associated with influenza vaccine responses in older adults

BACKGROUND: Vaccination helps prevent infections and associated sequelae, especially in older adults. Since the degree to which vaccine responses are influenced by medications is not well described, we examined the association of medication count, including statin or metformin use, with influenza vaccine responsiveness. METHODS: A secondary analysis of data from 542 participants aged 65 years and older randomized to receive either the standard or high dose vaccine during four influenza seasons (2015-2018) was conducted. Medication counts, as well as statin and metformin usage, were self-reported. Associations between vaccine antibody titer responses and medication usage were estimated using mixed model linear regression. RESULTS: Participants reported taking a median of five medications, with 45 % (n = 244) of participants using a statin and 12 % (n = 65) metformin. Medication use was higher with frailty, chronic condition count and in males. Our data showed that medication use was not broadly associated with vaccine responsiveness, which held after adjusting for frailty and number of chronic conditions, and when investigated within sex and vaccine dose strata. However, within diabetics, the strong boosting effect of the high-dose vaccine was significantly dampened for metformin users (n = 64) as compared to non-users (n = 30), but still remained slightly higher than standard-dose responses. This dampening effect was evident in analyses where all antigen-specific responses were combined (i.e. maxRBA, p = 0.002), and for responses against seasonal A/H3N2 (p = 0.007) and B (p = 0.03) antigens. CONCLUSION: Vaccine responses varied little with medication usage among older adults. However, our findings suggest metformin may be associated with reductions in the high-dose vaccine response within diabetics.