SARS-CoV-2 antibodies protect against reinfection for at least 6 months in a multicentre seroepidemiological workplace cohort

Abstract

Identifying the potential for SARS-CoV-2 reinfection is crucial for understanding possible long-term epidemic dynamics. We analysed longitudinal PCR and serological testing data from a prospective cohort of 4,411 United States employees in 4 states between April 2020 and February 2021. We conducted a multivariable logistic regression investigating the association between baseline serological status and subsequent PCR test result in order to calculate an odds ratio for reinfection. We estimated an odds ratio for reinfection ranging from 0.14 (95% CI: 0.019 to 0.63) to 0.28 (95% CI: 0.05 to 1.1), implying that the presence of SARS-CoV-2 antibodies at baseline is associated with around 72% to 86% reduced odds of a subsequent PCR positive test based on our point estimates. This suggests that primary infection with SARS-CoV-2 provides protection against reinfection in the majority of individuals, at least over a 6-month time period. We also highlight 2 major sources of bias and uncertainty to be considered when estimating the relative risk of reinfection, confounders and the choice of baseline time point, and show how to account for both in reinfection analysis.

Fig 1

(A) Number of PCR tests and PCR positive tests in the cohort between April 5, 2020 and January 31, 2021 from 3,296 participants. (B) Number of serological tests and seropositive tests between March 29, 2020 and August 23, 2020 from 4,411 participants. Data underlying this figure can be found in https://github.com/EmilieFinch/covid-reinfection.

Fig 2

(A) PCR positivity (%) in the cohort between April 5, 2020 and January 31, 2021. (B) Percentage ever seropositive in the cohort (number ever seropositive/cumulative number enrolled) between March 29, 2020 and August 23, 2020. Note that the percentage ever positive decreases initially as participants continue to be enrolled in the study. (C) Number of possible reinfections in cohort over time (defined as a new positive PCR test more than 30 days after initial seropositive result). (D) Odds ratio estimates comparing odds of reinfection in the seropositive group with odds of primary infection in the seronegative group, estimated using logistic regression and adjusted for potential confounders. The estimates are presented with their associated 95% CIs and with the cutoff week used to define baseline seroprevalence on the x-axis. Data underlying this figure can be found in https://github.com/EmilieFinch/covid-reinfection.

Fig 3

(A) Unadjusted odds ratio estimates comparing odds of reinfection in the seropositive group with odds of primary infection in the seronegative group. The estimates are presented with their associated 95% CIs and with the cutoff week used to define baseline seroprevalence on the x-axis. (B) Odds ratio estimates comparing odds of reinfection in the seropositive group with odds of primary infection in the seronegative group, estimated using logistic regression and adjusted for potential confounders. The estimates are presented with their associated 95% CIs and with the cutoff week used to define baseline seroprevalence on the x-axis. Data underlying this figure can be found in https://github.com/EmilieFinch/covid-reinfection.

Fig 4. Propensity to seek a PCR test between the seronegative and seropositive groups, for each cutoff week considered in the main analysis.

This was calculated as the percentage of those enrolled by the cutoff week shown on the x-axis who received at least 1 PCR test in the subsequent observation period. Data underlying this figure can be found in https://github.com/EmilieFinch/covid-reinfection.