Transmission of SARS-CoV-2 among children and staff in German daycare centers: results from the COALA study

Background: Whereas the majority of children under 6 years of age attend daycare centers in Germany, evidence on the role of daycare centers in the transmission of SARS-CoV-2 is scarce. Aims: This study aims to investigate the transmission risk in daycare centers among children and staff and the spread of infections to associated households. Methods: 30 daycare groups with at least one recent laboratory-confirmed SARS-CoV-2 case (child or staff) were enrolled in the study (10/2020-06/2021). Close contacts within the daycare group and households were examined over a 12-day period (repeated SARS-CoV-2 PCR tests, genetic sequencing of viruses, documentation of symptoms). Households, local health authorities and daycare staff were interviewed to gain comprehensive information on each outbreak. We determined primary cases for all daycare groups. Results: The number of secondary cases varied considerably between daycare groups. The pooled secondary attack rate (SAR) across all 30 daycare centers was 9.6%. The SAR tended to be higher in daycare centers in which the Alpha variant of the virus was detected (15.9% vs. 5.1% with evidence of wild type). The SAR in households was 53.3%. Exposed children were less likely to get infected with SARS-CoV-2 in daycare centers, compared to adults (7.7% vs. 15.5%). Conclusion: Containment measures in daycare programs are critical and become increasingly important with highly transmissible new variants to reduce SARS-CoV-2 transmission, especially to avoid spread to associated households. Virus variants may modify transmission dynamics in daycare programs.