Background: The strength and duration of immunity from infection with SARS-CoV-2 are important for public health planning and clinical practice.
Purpose: To synthesize evidence on protection against reinfection after SARS-CoV-2 infection.
Data sources: MEDLINE (Ovid), the World Health Organization global literature database, ClinicalTrials.gov, COVID19reviews.org, and reference lists.
Study selection: Longitudinal studies that compared the risk for reinfection after SARS-CoV-2 infection versus infection risk in individuals with no prior infection.
Data extraction: Two investigators sequentially extracted study data and rated quality.
Data synthesis: Across 18 eligible studies, reinfection risk ranged from 0% to 2.2%. In persons with recent SARS-CoV-2 infection compared with unvaccinated, previously uninfected individuals, 80% to 98% of symptomatic infections with wild-type or Alpha variants were prevented (high strength of evidence). In the meta-analysis, previous infection reduced risk for reinfection by 87% (95% CI, 84% to 90%), equaling 4.3 fewer infections per 100 persons in both the general population (risk difference, -0.043 [CI, -0.071 to -0.015]) and health care workers (risk difference, -0.043 [CI, -0.069 to -0.016]), and 26.6 fewer infections per 100 persons in care facilities (risk difference, -0.266 [CI, -0.449 to -0.083]). Protection remained above 80% for at least 7 months, but no study followed patients after the emergence of the Delta or Omicron variant. Results for the elderly were conflicting.
Limitation: Methods to ascertain and diagnose infections varied.
Conclusion: Before the emergence of the Delta and Omicron variants, persons with recent infection had strong protection against symptomatic reinfections for 7 months compared with unvaccinated, previously uninfected individuals. Protection in immunocompromised persons, racial and ethnic subgroups, and asymptomatic index case patients is unclear. The durability of protection in the setting of the Delta and Omicron variants is unknown.
Primary funding source: Agency for Healthcare Research and Quality. (PROSPERO: CRD42020207098).