COVID-19 cases have rarely been reported in children. We sought to analyse the attack rate in paediatric population in Poland, focusing on local variations among the provinces, correlation with the number of tests per capita, and test positivity rate.

Material and methods:
This cross-sectional study involved the 38.38 million population and detected 17,921 cases (age known in 17,822). Data were collected from publicly available registries and were analysed by age group and province of the country.

Children constituted 6.68% of cases (n = 1,191). The attack rate reached 15.49/100,000 children, increasing with age (10.79/100,000 in < 4 y.o. to 21.59/100,000 in 15–19 y.o.). Significant variations in the attack rates were observed: a 9.52-fold ratio between the highest and the lowest attack rates in provinces. The provinces from the first and fourth attack rate quartiles differed in the test positivity rate (4.96% vs. 1.98%, p < 0.05), but not in the number of tests per capita. The lowest quartile provinces showed 1.87- to 5.78-fold lower attack rates, compared to the directly neighbouring provinces, without any known population susceptibility differences. The attack rates in children and adults correlated very strongly (rho = 0.81). The attack rate correlated with the test positivity rate (rho = 0.64 in children and rho = 0.71 in adults) but not with the number of tests per capita.

COVID-19 burden in children is significant. The local differences highlight various testing strategies, but the awareness of SARS-CoV-2 in children is essential. The correlation between attack rates in children and adults shows that the outbreak in children is parallel to the one observed in adults.