Durability of Spike Immunoglobin G Antibodies to SARS-CoV-2 Among Health Care Workers With Prior Infection

This cohort study examines the durability of spike antibodies to SARS-CoV-2 among a cohort of US health workers.


Introduction
Herd immunity is needed to reduce deaths, prevent transmission, and minimize the emergence of SARS-CoV-2 variants.The durability of serum antibodies against the spike protein of this virus provides insights into immunologic memory following natural infection. 1Recent literature supports that the levels of spike antibodies induced by natural infection correlate with neutralization and protect against subsequent infection. 2We evaluated the durability of naturally acquired spike immunoglobin (Ig) G antibodies to SARS-CoV-2 among a cohort of health care workers.

Methods
Beginning in June 2020, 3015 hospital workers (HWs) at 5 regional hospitals in the Johns Hopkins Health System consented to participate and were enrolled in a prospective cohort study to determine the seroprevalence of spike antibodies to SARS-CoV-2.This study was approved by the Johns Hopkins University institutional review board.Cohort results followed the Strengthening the IgG measurement prior to vaccination were included in this analysis.Serum specimens were tested using an enzyme-linked immunosorbent assay (Euroimmun) that targets the S1 subunit of the SARS-CoV-2 spike protein and measures optical density ratios.We applied an internally derived IgG cutoff ratio (>1.23) for greater sensitivity and specificity with an upper threshold of 11 based on assay saturation. 3,4dian serum IgG ratios as a function of time (ie, days from positive PCR test) were visualized
a Demographic data for sex were collected through multiple choice survey questions.Listed options were male, female, and other.
b Demographic data for race were collected through multiple choice survey questions.Other was a listed option on the survey; multiple answers were allowed.

Discussion
Our results demonstrated the durability of spike antibodies to SARS-CoV-2 up to 10 months after natural infection.The Centers for Disease Control and Prevention acknowledges that prior SARS-CoV-2 infection reduces the risk of reinfection for a minimum 90-day period.Our data demonstrate durability of IgG titers well beyond this period and extend recently published intervals of 6 to 8 months. 2,5is study was limited by its use of a convenience sample nested within a longitudinal cohort of hospital workers, which means results may not be generalizable.Additional studies are also needed to determine whether antibody levels represent lasting immunity to the evolving SARS-CoV-2.
As vaccine supply remains limited globally, those with naturally derived antibodies may contribute to herd immunity.Therefore, some countries may consider prioritizing vaccination for those without measurable antibodies, a strategy used in prior vaccination campaigns when shortages exist. 6However, more research is needed to understand protection against emerging variants based on natural vs vaccine-derived immunity.
Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.Data were analyzed March 2021.Participants provided serum samples and completed surveys (including providing demographic data and exposures) every 3 to 4 months after enrollment.SARS-CoV-2 polymerase chain reaction (PCR)-testing and immunization data were collected from electronic health records.A convenience sample of HWs who tested positive for SARS-CoV-2 and then had at least 1 positive anti-SARS-CoV-2 using a natural cubic spline (with 2 df) with 95% bootstrap CIs to account for multiple serum samples within HWs.A linear mixed model with random intercept for each HW quantified the relative change in serum IgG ratio per day from a positive PCR test.A sensitivity analysis, including only HWs with multiple serum samples, estimated the within-participant relative change in IgG by separating the cross-sectional and longitudinal effect of time.Analysis was conducted using R version 4.0.2(R Project for Statistical Computing).The threshold for statistical significance was α < .05 in 2sided tests.