A Systematic Review of the Protective Effect of Prior SARS-CoV-2 Infection on Repeat Infection

Abstract

Introduction: We systematically reviewed studies to estimate the risk of SARS-CoV-2 reinfection among those previously infected with SARS-CoV-2. Methods: For this systematic review, we searched scientific publications on PubMed and, the pre-print server, MedRxiv through August 18, 2021. Eligible studies were retrieved on August 18, 2021. We used the following search term on PubMed: (((Cohort Studies [Majr]) AND (COVID-19 [Mesh] OR SARS-CoV-2 [Mesh])) OR Reinfection [Majr]) OR Reinfection [Mesh]. We used the following search term on MedRxiv: Cohort Studies AND COVID-19 OR SARS-CoV-2 AND Reinfection. The search terms were broad to encompass all possibilities for applicable studies. There were no restrictions on the date of publication. Studies that did not describe cohorts with estimates of the risk of SARS-CoV-2 reinfection among those with previous infection were excluded. Studies that included vaccinated participants were either excluded or limited to sub-groups of non-vaccinated individuals. To identify relevant studies with appropriate control groups, we developed the following criteria for studies to be included in the systematic analysis: (1) baseline polymerase chain reaction (PCR) testing, (2) a negative comparison group, (3) longitudinal follow-up, (4) a cohort of human participants, i.e., not a case report or case series, and (5) outcome determined by PCR. The review was conducted following PRISMA guidelines. We assessed for selection, information, and analysis bias, per PRISMA guidelines. Results: We identified 1,392 reports. Of those, 10 studies were eligible for our systematic review. The weighted average risk reduction against reinfection was 90.4% with a standard deviation of 7.7%. Protection against SARS-CoV-2 reinfection was observed for up to 10 months. Studies had potential information, selection, and analysis biases. Conclusions: The protective effect of prior SARS-CoV-2 infection on re-infection is high and similar to the protective effect of vaccination. More research is needed to characterize the duration of protection and the impact of different SARS-CoV-2 variants.

A systematic review of COVID-19 vaccine efficacy and effectiveness against SARS-CoV-2 infection and disease

“…Unvaccinated individuals previously infected with SARS-CoV-2 have some protection against re-infection, estimated in recent study to be ∼90% 185,186 . Consequently, including previously-infected persons in the unvaccinated group of studies could bias estimates of effectiveness downward.…”

Effect of prior infection, vaccination, and hybrid immunity against symptomatic BA.1 and BA.2 Omicron infections and severe COVID-19 in Qatar

“…SARS-CoV-2 reinfection is conventionally defined as a documented infection ≥90 days after an earlier infection, to avoid misclassification of prolonged PCR positivity as reinfection, if a shorter time interval is used. 3,30,31 Prior infection was thus defined as a PCR-positive test ≥90 days before this study’s PCR test. Individuals with a PCR-positive test <90 days before the study’s PCR test were excluded from both cases and controls.…”

Protection of Omicron sub-lineage infection against reinfection with another Omicron sub-lineage

“…Ideally, SARS-CoV-2 reinfection is defined as a documented infection ≥90 days after an earlier infection, to avoid misclassification of prolonged infections as reinfections, if a shorter time interval is used. [20][21][22] Since the Omicron wave started only few weeks ago, this definition could not be used. Analysis of durations of follow-up was conducted to identify the longest time interval possible while maintaining adequate durations of follow-up and precision of estimates.…”