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An unresolved question about COVID-19 is whether prior infection with non–SARS-CoV-2 coronaviruses provides cross-reactive protective humoral or cell-mediated immunity to SARS-CoV-2. The existence of such immunity is supported by the observation that, before vaccine rollout, young children with recent prior coronavirus infections were less likely to need hospitalization or ICU care for COVID-19. To assess this possibility in adults, researchers used data from the Kaiser Permanente Northern California integrated healthcare delivery system to determine risk for severe COVID-19 in adults living with or without children through January 2021. They performed 1:1 propensity matching of adults without children to those with children aged 0–5 years, 6–11 years, and 12–18 years; risk factors for severe COVID-19 included age, race/ethnicity, comorbidities, and socioeconomic status.
Of >3.1 million adults, 743,814 had children and 274,316 had a child aged 0–5 years. Rates of COVID-19 infection were slightly higher in adults living with children aged 6–11 and 12–18 years compared to those living with children aged 0–5 years, but rates of severe COVID-19 did not differ. However, compared to adults living with children aged 0–5 years, those without children had significantly lower rates of COVID-19 infections (p<0.0001) but significantly higher rates of hospitalizations (p=0.0014) and ICU admissions for COVID-19 (p=0.0437).
Solomon MD et al. Risk of severe COVID-19 infection among adults with prior exposure to children. Proc Natl Acad Sci U S A 2022 Aug 16; 119:e2204141119. (https://doi.org/10.1073/pnas.2204141119)
Comment
As the authors note, study limitations included potentially failing to control for important confounding factors and possibly misclassifying adult exposures to children. Still, given the high likelihood that adults living with children aged 0–5 years would have contracted a recent coronavirus infection, the findings suggest that cross-reactive protection against severe COVID-19 does develop. This is consistent with current pandemic experiences in which new SARS-CoV-2 variants have been associated with higher rates of infection, but lower rates of severe disease.