Near real-time safety surveillance of COVID-19 vaccines during vaccine rollout is necessary.

A web-based prospective cohort analysis of patient-reported outcomes is useful for vaccine surveillance.

Well-known systemic adverse events following immunization (AEFIs) were most often experienced by participants receiving the first dose of the AstraZeneca vaccine and the Janssen vaccine and the second dose of the Moderna vaccine.

The frequency of serious AEFIs was low (approximately 0.228% for the first dose of the AstraZeneca vaccine).

Participants with a history of COVID-19 infection, women and younger people experienced at least one well-known systemic AEFI more often than their counterparts.