COVID-19 was protective against reinfection during a second outbreak of This study was not included in the 2021 systematic review study above. Patients were nursing/care home staff (n5106, no further demographics presented) and residents (n5103, median age 84 years old, about two-thirds female) from two London nursing/ care homes. Previous infection was confirmed with either RT-PCR or antibody tests. The primary outcome was infection with COVID-19 during the second outbreak, determined by a positive RT-PCR test. Patients with an initial COVID-19 infection had a significantly lower incidence of infection compared with those without antibodies (1.1% vs 30.1%; relative risk [RR] 0.04; 95% CI, 0.01-0.27).A 2022 surveillance study (n5550,168) examined the protection of prior COVID-19 infection against reinfection. 4 Patients were 20 years old and older and 56% female. Patients included in this study were identified as either having tested positive or negative for COVID-19 between March 6 and August 31, 2020. Patients who died within 90 days of their initial positive test were excluded. Patients with initial positive COVID-19 tests (n541,647) composed the positive test group and were followed for recurrence of a positive test from 91 days after initial result through December 31, 2020. Patients with a negative test and no subsequent positive test within the study period (n5508,521) composed the testnegative comparison group. The primary outcome was either a positive COVID-19 test by PCR or antigen tests, date of death, or until December 31, 2020. Patients with no previous infection had a significantly higher risk of a positive test compared with individuals with a history of infection (1.4% vs 6.3%; RR 4.4, 95% CI,. This corresponded to a protective effect of 77.3% (95% CI, 75.4%-79.0%) from repeat infection. Study limitations included differences in risk behaviors between cohort groups, and use of antigen testing without confirmation with PCR testing.