• A retrospective cohort study was recently published in the journal Clinical Infectious Diseases which suggested that previous infection with COVID-19 protects against reinfection and symptomatic disease.
• The study of one multi-hospital health system included 150,325 patients who were tested for COVID-19 through PCR between March 12 and August 30, 2020. Testing performed up to February 24, 2021 in these patients was included for evaluation. The main outcome measure included reinfection (infection ≥ 90 days after initial testing). Secondary outcomes included symptomatic infection and protection of prior infection against reinfection.
• Among the recruited patients, 5.9% tested positive and 94.1% tested negative before August 30. Around 14.4% of the positive patients were retested 90 days later, and 62 appeared to have possible reinfection. Thirty one of these (50%) were symptomatic. Of the participants with an initial negative testing, 5,449 (3.9%) were subsequently found to be positive; 3,191 of these (58.5%) were symptomatic. Protection offered from prior infection was 81.8%, and against symptomatic infection was 84.5%. The protection was found to increase over time.
• Prior infection in patients with COVID-19 was thus reported to be highly protective against reinfection and symptomatic disease. 
• The protection increased over time. The findings suggest that viral shedding or ongoing immune response may persist after 90 days and may not indicate true reinfection. 
• Considering limited vaccine supply, patients with history of COVID-19 could delay early vaccination in order to enable the most vulnerable to have access to the vaccines and decrease transmission.

 (Clin Infect Dis. 2021 Mar 15)

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA