Risk of SARS-CoV-2 reinfections in children: prospective national surveillance, January 2020 to July 2021, England
Authors: Mensah Anna A , Campbell Helen , Stowe Julia , Seghezzo Giulia , Simmons Ruth , Lacy Joanne , Bukasa Antoaneta , O’Boyle Shennae , Ramsay Mary E , Brown Kevin , Ladhani Shamez 
Published: December 2021

AbstractBackgroundReinfection after primary SARS-CoV-2 infection is uncommon in adults, but little is known about the risks, characteristics, severity or outcomes of reinfection in children.MethodsWe used national SARS-CoV-2 testing data in England to estimate the risk of reinfection ≥90 days after primary infection from 01 January 2020 to 31 July 2021, which encompassed both the Alpha and Delta waves in England. Disease severity was assessed by linking reinfection cases to national hospitalisation, intensive care admission and death registrations datasets.FindingsReinfection rates closely followed community infection rates, with a small peak during the Alpha wave and a larger peak during the Delta wave. In children aged ≤16 years, there were 688,418 primary infections and 2,343 reinfections. The overall reinfection rate was 66·88/100,000 population, being higher in adults (72.53/100,000) than in children (21·53/100,000). Reinfection rates after primary infection were 0·68% overall, 0·73% in adults and 0·34% in children. Of the 109 reinfections in children admitted to hospital, 78 (72%) had underlying comorbidities. Hospitalisation rates were similar for the first (64/2343, 2·73%) and second episode (57/2343, 2·43%). Intensive care admission was rare after primary infection (n=7) or reinfection (n=4), mainly in children with comorbidities. 44 deaths occurred after primary infection within 28 days of diagnosis (44/688,418, 0·01%), none after possible reinfections.InterpretationThe risk of SARS-CoV-2 reinfection is strongly related to exposure due to community infection rates, especially during the Delta variant wave. Children had a lower risk of reinfection than adults, but reinfections were not associated with more severe disease or fatal outcomes.FundingPHE/UKHSAResearch in ContextEvidence Before this studyWe searched PubMed with the terms “COVID-19” or “SARS-CoV-2” with “reinfection” to identify publications relating to SARS-CoV-2 reinfections from 01 January until 15 November 2021. There were few publications relating to SARS-CoV-2 reinfections, and these primarily related to adults. Published studies reported very low rates of reinfection during the first few months after primary infection in adults. COVID-19 vaccines provide effective immune protection against SARS-CoV-2 infection, but recent studies have reported increasing risk of breakthrough infection with time since primary vaccination due to waning immunity. Several SARS-CoV-2 variants, including the beta, gamma and delta variants have been shown to partially evade immunity after natural infection and vaccination, potentially increasing the risk of reinfections and breakthrough infections, respectively. Data on reinfections in children are lacking and restricted mainly to case reports in immunocompromised children.Added Value of This StudyWe used national SARS-CoV-2 testing data during the first 19 months of the pandemic to estimate the risk of reinfection in children compared to adults during a period that encompassed both the Alpha and the Delta variant waves in England. We found that the risk of reinfection correlated with the risk of SARS-CoV-2 exposure and therefore, closely reflected community infection rates, with most reinfections occurring during the Delta variant wave. Whilst acknowledging the limitation of using national testing data, we found that children had a lower risk of reinfection compared to adults and that the risk of reinfection in children increased with age. Reinfections were not associated with severe disease in terms of hospitalization or intensive care admission and there were no fatalities within 28 days of the reinfection episode in children.Implications of all the Available EvidenceSARS-CoV-2 reinfections are rare in children, especially younger children, and occurred mainly during the Delta wave in England. Reinfections were not associated with more severe disease or fatal outcomes in children. COVID-19 vaccination will provide further protection against primary infections and reinfections in children.