This article, published in February 2021, shows a large multi-center prospective study done in 2020 in England. At enrollment, participants were assigned to either the positive cohort ( people who had COVID-19-antibody positive or prior PCR/antibody test positive) or negative cohort (people who never had COVID-19 antibody negative, not previously known to be PCR/antibody positive). Participants underwent regular SARS-CoV-2 PCR and antibody testing (every 2-4 weeks) and completed frequent questionnaires on symptoms and exposures.
The incidence of positive COVID-19 cases per 100,000 person days between June and November 2020 was 3.2 reinfections in the positive cohort, compared with 22.4 infections in the negative cohort.
A prior history of SARS-CoV-2 infection was associated with an 83% lower risk of infection, the observed time after original infection was 5 months. This study clearly shows the importance of a history of prior infection when evaluating the risk of a new infection and the need for vaccination. Keep in mind that this study was done during 2020