In a recent study published on the preprint server medRxiv*, researchers evaluated protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection.
Study: Immune protection against SARS-CoV-2 reinfection and immune imprinting. Image credit: eamesBot/Shutterstock
In general, the global population has a heterogeneous immune history due to multiple exposures to SARS-CoV-2 variants and vaccinations. Evidence suggests that prior SARS-CoV-2 infection could negatively imprint subsequent protective immunity. Specifically, immune responses against Omicron SARS-CoV-2 subvariants could be compromised due to differential imprinting in individuals with prior infection with ancestral SARS-CoV-2 or pre-Omicron variants.
About the study
The present study investigated the epidemiological evidence of immune imprinting in the Qatari population. The researchers obtained data on SARS-CoV-2 laboratory testing, vaccination, hospitalization, and deaths from the National Digital Health Information Platform.
The incidence of SARS-CoV-2 reinfection with Omicron BA.1 or BA.2 in individuals previously infected with pre-Omicron variants (reinfection cohort) was compared with the incidence of reinfection in individuals with a primary infection documented by Omicron (primary infection cohort). ).
Individuals with a documented reinfection from December 19, 2021 to August 15, 2022 were included in the reinfection cohort. In the same period, those with primary infection (Omicron) were included in the primary infection cohort. The primary outcome of the study was the incidence of SARS-CoV-2 infection; Secondary outcomes included the incidence of severe, critical or fatal coronavirus disease 2019 (COVID-19).
Individuals in the reinfection cohort were exactly 1:3 matched to those in the primary infection cohort by sex, nationality, comorbidities, and calendar week of primary infection or reinfection. Reinfection was defined as the recurrence of infection a minimum of 90 days after the primary infection. Subjects were followed until documented SARS-CoV-2 infection, vaccination, or death.
The team calculated the cumulative incidence of infection using the Kaplan-Meier estimator method. Hazard ratios (HR) and corresponding 95% confidence intervals were estimated using Cox regression, adjusting for concordant variables. In addition, subgroup analysis was performed to calculate HRs adjusted for time since reinfection.
discoveries
After matching, the reinfection cohort consisted of 7,873 individuals, while the primary infection cohort had 22,349 subjects, all of whom were unvaccinated. There were 63 and 343 reinfections in the reinfection and primary infection cohorts, respectively. None of the two cohorts developed severe COVID-19 outcomes. The cumulative incidence of SARS-CoV-2 infection was 1.1% and 2.1% for the reinfection and primary infection cohorts, respectively, after 135 days of follow-up.
When the incidence of infection was compared between the two cohorts, the adjusted HR was estimated at 0.52. The adjusted HR was 0.59 in a subgroup analysis where primary infections in the reinfection cohort were limited to ancestral SARS-CoV-2 or the Alpha variant. Adjusted HR was 0.92 in the first 70 days of follow-up when Omicron BA.2 was prevalent.
About 45% and 38% of subjects in the reinfection and primary infection cohorts underwent SARS-CoV-2 testing during the follow-up period, with a frequency of 0.79 and 0.64 tests/individual , respectively. After adjusting for testing frequency between the two cohorts, the HR was 0.42, confirming the findings.
Conclusions
The study found no evidence that immune imprinting compromised protective immunity against Omicron SARS-CoV-2 subvariants. The authors found that primary infection with pre-Omicron variants and reinfection with Omicron resulted in stronger protection against later Omicron subvariants than (primary) infection with Omicron alone.
In particular, undocumented or undocumented infections might have boosted immune responses, given that only documented infections were examined. Furthermore, the findings could not be generalized to populations in other countries and older adults because the majority of the population in Qatar is predominantly young.
*Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.