RESUMEN
We report a decentralized prospective cohort study of self-reported adverse events and antibody responses to COVID vaccines derived from dried blood spots. Data is presented for 911 older (aged >70 years) and 375 younger (30-50 years) recruits to 48 weeks after the primary vaccine series. After a single vaccine, 83% younger and 45% older participants had overall seropositivity (p<0.0001) increasing to 100/98% with the second dose respectively (p=0.084). A cancer diagnosis (p=.009), no mRNA1273 vaccine doses (p<.0001) and older age (p <.0001) predicted lower responses. Antibody levels declined in both cohorts at 12 and 24 weeks increasing with booster doses. At 48 weeks, for participants with 3 vaccine doses, the median antibody levels were higher in the older cohort (p=.04) with any dose of mRNA-1273 (p<.0001) and with COVID infection (p<.001). The vaccines were well tolerated. Breakthrough COVID infections were uncommon (16% older cohort, 29% younger cohort;p<0.0001) and mild. Graphical abstract