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Past SARS-CoV-2 Infection Protection Against Reinfection: A Systematic Review and Meta-Analysis
31 Pages Posted: 6 Jul 2022
More...Abstract
Background: Understanding the level and characteristics of protection from past SARS-CoV-2 infection against subsequent COVID-19 infection, symptomatic disease, and severe disease is essential for predicting future potential disease burden and for designing policies that restrict, on the basis of immune status, travel or access to venues where there is a high risk of transmission.
Methods: We systematically reviewed, identified, and extracted from the scientific literature studies that estimated the reduction in risk of COVID-19 among individuals with a past SARS-CoV-2 infection in comparison to those without a previous infection. We meta-analysed the effectiveness of past infection by outcome (infection, symptomatic disease, and severe disease), variant, and time since infection. A Bayesian meta-regression has been run to estimate the pooled estimates of protection. The systematic review is PRISMA-compliant and is registered with PROSPERO.
FindingsWe identified a total of 43 studies from 17 different countries. Our meta-analyses show that protection from recent infection and any symptomatic disease was high for ancestral, Alpha, Beta, and Delta variants but was substantially lower for the Omicron variant. Pooled effectiveness against reinfection by the Omicron variant was 38.8% (95% uncertainty interval [UI] 31.5–46.3) and 43.7% (18.4–74.4) against Omicron symptomatic disease. Mean pooled effectiveness was greater than 85% against severe disease (hospitalisation and death) for all variants, including Omicron. Protection from reinfection from ancestral, Alpha, and Delta variants declined over time but remained at 78.2% (38.9–95.1) at 40 weeks. Protection against reinfection by the Omicron variant declined more rapidly and was estimated at 29.0% (10.4–64.4) at 40 weeks. There were not enough data to estimate protection against symptomatic disease and severe disease considering time since infection.
Interpretation: Protection from past infection against reinfection from pre-Omicron variants was very high and remained high even after 40 weeks. Protection was substantially lower for the Omicron variant and declined more rapidly over time in comparison to previous variants. The immunity conferred by past infection should be weighed alongside protection from vaccination when assessing future disease burden from COVID-19 and when designing policies that mandate vaccination for workers or restrict access, on the basis of immune status, to settings where the risk of transmission is high, such as travel and high-occupancy indoor settings.
Registration: The systematic review is PRISMA-compliant and is registered with PROSPERO.
Funding: Bill & Melinda Gates Foundation, J. Stanton, T. Gillespie, and J. and E. Nordstrom.
Declaration of Interest: All other authors declare no competing interests.
Keywords: COVID-19, SARS-CoV-2, SARS-CoV-2 variants, Systematic Review, Meta-Analysis
Suggested Citation: Suggested Citation