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Protective Effect Conferred by Prior Infection and Vaccination on COVID-19 in a Healthcare Worker Cohort in South India

23 Pages Posted: 31 Aug 2021

See all articles by Malathi Murugesan

Malathi Murugesan

Christian Medical College

Prasad Mathews

Christian Medical College

Hema Paul

Christian Medical College

Rajiv Karthik

Christian Medical College - Department of Infectious Diseases

Joy John Mammen

Christian Medical College - Department of Transfusion Medicine and Immunohaematology

Priscilla Rupali

Christian Medical College - Department of Infectious Diseases

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Abstract

Background: The emergence of newer variants with the immune escape potential raises concerns about breakthroughs and re-infections resulting in future waves of infection. We examined the infection rates among a cohort of healthcare workers (HCW) in South India during the second wave driven mainly by the delta variant and examined the protective effect of prior COVID-19 disease and vaccination.  

Methods: Symptomatic HCWs were routinely tested by RT-PCR per institutional policy. Vaccination was offered to all HCWs between January and June 2021, and the details were documented. We set up a non-concurrent cohort to estimate infection rates and estimated efficacy of prior infection and vaccination between 16th Apr to 30th May, 2021, using a cox-proportional hazards model with time-varying covariates adjusting for daily incidence. 

Findings: Between June 2020 and May 2021, 2735 (23.9%) of 11,405 HCWs were infected, with 1412, including 32 re-infections, reported during the second wave. 6863 HCWs received two doses of vaccine and 1905 one dose. The protective efficacy of prior infection against symptomatic infection was 86.0% (95%CI 76.7% - 91.6%). Vaccination combined with prior infection provided 91.1% (95%CI 84.1% - 94.9%) efficacy. In the absence of prior infection, vaccine efficacy against symptomatic infection during the second wave was 31.8% (95%CI 23.5% – 39.1%). 

Interpretation: Prior infection provided substantial protection against symptomatic re-infection and severe disease during a delta variant driven second wave. Deferring vaccination for previously symptomatically infected individuals is a pragmatic strategy to overcome vaccine supply constraints. However, the duration of protection requires further evaluation.

Funding None to declare.

Declaration of Interest: None to declare.

Ethical Approval: This study was approved by the institutional ethics committee and research
board (IRB Min no. 13980).

Suggested Citation

Murugesan, Malathi and Mathews, Prasad and Paul, Hema and Karthik, Rajiv and Mammen, Joy John and Rupali, Priscilla, Protective Effect Conferred by Prior Infection and Vaccination on COVID-19 in a Healthcare Worker Cohort in South India. Available at SSRN: https://ssrn.com/abstract=3914633 or http://dx.doi.org/10.2139/ssrn.3914633

Malathi Murugesan

Christian Medical College ( email )

Vellore, Tamil Nadu
India

Prasad Mathews

Christian Medical College ( email )

Vellore, Tamil Nadu
India

Hema Paul

Christian Medical College ( email )

Vellore, Tamil Nadu
India

Rajiv Karthik

Christian Medical College - Department of Infectious Diseases ( email )

Joy John Mammen

Christian Medical College - Department of Transfusion Medicine and Immunohaematology ( email )

Vellore, Tamil Nadu 632004
India
+91 416 228 2536 (Phone)
+91 416 223 2035 (Fax)

Priscilla Rupali (Contact Author)

Christian Medical College - Department of Infectious Diseases ( email )

Tamil Nadu
India

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