Mobile-app-based cohort event monitoring study (CEM) of COVID-19 vaccines

Vaccine pharmacovigilance is critically important to ensure transparent information related to vaccine safety. We conducted a prospective, non-interventional, population-based cohort study, SafeVac2.0, in order to supplement passive surveillance of COVID-19 vaccines by collecting self-reported adverse events (AEs). Participation via smartphone app was allowed within 48 h after the administration of the first or second dose of a COVID-19 vaccine. Adverse events were collected up to 3 weeks after the first vaccination, 8 weeks after the second vaccination, and 7 days after the booster dose. Participants were also asked about their health condition 6 and 12 months after the first dose registered. The study was conducted from December 26, 2020 to September 30, 2022. A total of 739,216 persons met the primary inclusion criteria, of which 732,864 documented at least one vaccination. Data on 1,436,039 vaccinations were collected. At least one AE was reported for 68% of the vaccinations and in total 4,007,149 AEs were reported. 88% of AEs consisted of solicited local and systemic reactogenicity. Age, sex, vaccine product and dose were potential predictors for solicited adverse events. The need for medical care was reported in 0.36% of vaccinations. Overall, the study results provide reassurance of the safety profile of COVID-19 vaccines. The use of a native app to monitor self-reported adverse events represents an innovative pharmacovigilance approach.