COVID-19 vaccine safety studies- the need for a third group for extended monitoring.

Introduction: Studies assessing COVID-19 vaccine effectiveness have generally categorized individuals into 'vaccinated' and 'unvaccinated' groups. Long-term safety studies are sparse and have usually compared adverse events with background rates. Studies on timing of COVID-19 vaccination as a determinant of long COVID have provided variable results, while there is scarce data on timing of vaccination as a determinant of adverse events.

Areas covered: We discuss some of our observations as well as the global evidence on the timing of COVID-19 vaccination as a determinant of long-COVID and adverse events. This special report is hypothesis-generating and aims to propose a conceptual framework and not establish causality.

Expert opinion: We propose an alternative classification strategy for COVID-19 vaccinees, with special emphasis on individuals who received any dose of vaccination after recovering from natural COVID-19, i.e. the 'vaccine-after-COVID' (VAC) group. These individuals should be followed up for an extended period through multicentric and database studies. This may help in understanding the long-term safety of COVID-19 vaccines and the natural course of long COVID. Immunological characteristics of this group should also be scrutinized. The evidence gained might be useful in planning vaccination policies in the event of future pandemics.