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The possibility of SARS-CoV-2 reinfection in COVID-19 survivors is recognized, but the rate and severity of such episodes (and the associated immunologic risk factors) remain unclear. Two recent studies add some evidence.
In a retrospective observational study of >75,000 California HMO members with PCR-confirmed COVID-19 diagnoses between March and October 2020, Slezak et al. assessed subsequent positive SARS-CoV-2 tests >90 days after initial infection (indicating reinfection) through January 2021 (mean follow-up, 270 days). Among 315 individuals with suspected reinfection, more were women than men (1.0% vs. 0.7%, P=0.002; adjusted hazard ratio [HR], 1.4). Other significant risk factors included immunocompromising conditions (HR, 2.5), hospitalization during initial infection (HR, 1.6), initial infection after March/May 2020 (HR, 1.3 [June/August]; HR, 2.3 [September/October]), and adult age (HR range, 2.2–2.7). Rates of hospitalization were higher for reinfection than for initial infection (11.4% vs. 5.4%).
Peghin et al. followed 546 individuals (mean age, 53; 54% female) with COVID-19 diagnoses at a single Italian medical center between March and May 2020; prospective follow-up involved monthly serologic testing for a median 10 months. IgG seroconversion at 2 months ranged from 100% (moderately to critically ill patients) to 54% (asymptomatic patients). At 10 months, 47% of participants had loss of detectable antibodies. Reinfection occurred in six individuals a median of 9 months after the initial infection. Of these, two were seronegative, two had seroreverted, and two were seropositive. All six had had mild initial infections and were mildly symptomatic or asymptomatic during reinfection.
Slezak J et al. Rate and severity of suspected SARS-CoV-2 reinfection in a cohort of PCR-positive COVID-19 patients. Clin Microbiol Infect 2021 Jul 28; [e-pub]. (https://doi.org/10.1016/j.cmi.2021.07.030)
Peghin M et al. Low risk of reinfections and relation with serological response after recovery from the first wave of COVID-19. Eur J Clin Microbiol Infect Dis 2021 Aug 11; [e-pub]. (https://doi.org/10.1007/s10096-021-04335-x)
Comment
Taken together, these studies point to a 1% risk for reinfection after an episode of COVID-19. The mechanisms underlying certain factors associated with reinfection (e.g., excess risk in women) need further investigation. Other factors seem more readily explained (e.g., excess risk in immunocompromised patients), but elucidating risk for reinfection despite full vaccination in COVID-19–naive individuals is imperative. My own (Infection 2021 Sep 25) and other research has demonstrated a considerable rise of anti-SARS-CoV-2 antibody levels in COVID-19 survivors after booster vaccination, which will likely lower risk for reinfection further than relying on natural immunity alone.