Protection afforded by prior infection against SARS-CoV-2 reinfection with the Omicron variant

Abstract

BACKGROUND: Natural SARS-CoV-2 infection elicits strong protection against reinfection with the Alpha (B.1.1.7), Beta (B.1.351), and Delta (B.1.617.2) variants. However, the Omicron (B.1.1.529) variant harbors multiple mutations that can mediate immune evasion. We estimated effectiveness of prior infection in preventing reinfection (PES) with Omicron and other SARS-CoV-2 variants in Qatar. METHODS: PES was estimated using the test-negative, case-control study design, employing a methodology that was recently investigated and validated for derivation of robust estimates for PES. Cases (PCR-positive persons with a variant infection) and controls (PCR-negative persons) were exact-matched by sex, 10-year age group, nationality, and calendar time of PCR test, to control for known differences in the risk of exposure to SARS-CoV-2 infection in Qatar. RESULTS: PES against symptomatic reinfection was estimated at 90.2% (95% CI: 60.2-97.6) for Alpha, 84.8% (95% CI: 74.5-91.0) for Beta, 92.0% (95% CI: 87.9-94.7) for Delta, and 56.0% (95% CI: 50.6-60.9) for Omicron. Only 1 Alpha, 2 Beta, 0 Delta, and 2 Omicron reinfections progressed to severe COVID-19. None progressed to critical or fatal COVID-19. PES against hospitalization or death due to reinfection was estimated at 69.4% (95% CI: -143.6-96.2) for Alpha, 88.0% (95% CI: 50.7-97.1) for Beta, 100% (95% CI: 43.3-99.8) for Delta, and 87.8% (95% CI: 47.5-97.1) for Omicron. CONCLUSIONS: Protection afforded by prior infection in preventing symptomatic reinfection with Alpha, Beta, or Delta is robust, at about 90%. While such protection against reinfection with Omicron is lower, it is still considerable at nearly 60%. Prior-infection protection against hospitalization or death at reinfection appears robust, regardless of variant.

Increased risk of infection with SARS-CoV-2 Omicron BA.1 compared with Delta in vaccinated and previously infected individuals, the Netherlands, 22 November 2021 to 19 January 2022

“…This contrasts with what we observed in a previous analysis, where we did not find an increased risk of infection with the Delta, Beta (B.1.351) and Gamma (P.1) variants vs the Alpha variant in previously infected individuals [ 21 ]. Our finding of reduced protection against reinfection with Omicron is in line with reports showing increased risk of reinfections with the Omicron variant [ 22 - 24 ].…”

SARS-CoV-2 Omicron symptomatic infections in previously infected or vaccinated South African healthcare workers

“…We show that prior SARS-CoV-2 infection prevented symptomatic reinfection with Omicron at 45%-60%, what is consistent with results from a large population study in Qatar [7]. Although it has been suggested that Omicron is evasive to neutralizing antibodies induced by natural infection from previous variants or vaccine-elicited[8], we show that HCW who were not infected by Omicron during the five week period of this analysis had higher concentration of anti-spike IgG prior the symptomatic visit, with >1549BAU/mL being the threshold suggestive of significant reduction in the risk of symptomatic Omicron infection.…”

Clinical outcomes associated with Omicron (B.1.1.529) variant and BA.1/BA.1.1 or BA.2 subvariant infection in southern California

“…We have quantified two aspects of comparative severity of Omicron vs. Delta variant infections: the risk of progression to severe endpoints among diagnosed cases, and the risk of progression to acute respiratory symptoms among those first diagnosed before symptoms onset. While attenuation of disease severity in association with the Omicron variant is an encouraging finding, prior evidence of higher transmissibility of Omicron variant infections [27], as well as immune evasion from prior infection [28] and vaccination [6–8], are concerning. Rapid spread of the Omicron variant in a compressed time period has led to unprecedented surges in COVID-19 among our study population and others globally.…”