Prior SARS-CoV-2 infection and risk of subsequent COVID-19-related hospitalization: a test negative design

ABSTRACT

Background. Studies show that past SARS-CoV-2 infection provides a protective immune response against subsequent COVID-19, but the degree of protection from prior infection has not been determined. History of previous SARS-COV-2 Infection and Current SARS-COV-2 Infection Status at Admission. *Adjusted for chronic respiratory disease and prior COVID-19 vaccination Methods. From May 2021 through Feb 2022, adults (>= 18 years of age) hospitalized at Emory University Hospital and Emory University Hospital Midtown with acute respiratory infection (ARI) symptoms, who were PCR tested for SARS-CoV-2 were enrolled. A prior history of SARS-CoV-2 infection was obtained from patient interview and medical record review. Previous infection was defined as a self-reported prior SARS-CoV-2 infection or previous evidence of a positive SARS-CoV-2 PCR test >= 90 days before ARI hospital admission. We performed a test negative design to evaluate the protection provided by prior SARS-CoV-2 infection against subsequent COVID-19-related hospitalization. Effectiveness was determined using logistic regression analysis adjusted for patient sociodemographic and clinical characteristics and COVID-19 vaccination status. Results. Of 1152 adults hospitalized for ARI, 704/1152 (61%) were SARS-CoV-2 positive. 96/1152 (8%) had a prior SARS-CoV-2 infection before hospital admission. Patients with a previous history of SARS-CoV-2 infection were less likely to test positive for SARS-CoV-2 upon admission for ARI compared to those who did not have evidence of prior infection (31/96 [32%] vs 673/1056 [64%];adjustedOR 0.25 [0.15, 0.41] (Table). Conclusion. Reinfections represented a small proportion (< 10%) of COVID-19-related hospitalizations. Prior SARS-CoV-2 infection provided meaningful protection against subsequent COVID-19-related hospitalization. The durability of this infection-induced immunity, variant-specific estimates, and the additive impact of vaccination are needed to further elucidate these findings.