Study of family clusters of COVID-19 in the Ústí nad Labem Region with a focus on children - clinical picture, secondary transmission, antibody response.

Objective: The article presents the results of a study of family clusters of COVID-19 whose aim was to describe the clinical course of the disease in children, to identify secondary transmission in households with infected children, and to find out the differences in the antibody response between children and adults. Data were collected from 3 March 2020 to 25 October 2020, that is at the time when the alpha or delta variants were not dominant.

Methods: A retrospective analysis of data on infected children in the Ústí nad Labem Region collected by the Regional Public Health Authority along with questionnaire data reported by their families. Serological tests were performed in study volunteers.

Results: The most common symptoms in children were headache, runny nose, and loss of smell and taste. The hospital admission rates were 0.8% in children and 2.4% in adults. The secondary transmission rate in families where the index case was a child reached 22.6%. It was higher when the index case was a child 11-15 years of age or asymptomatic. The secondary transmission rate in families where the index case was an adult equalled 77.1%. Children had higher IgG antibody levels than adults at post-infection months 4 and 5, but their seropositivity rate was comparable to that of adults.

Conclusion: Children have a nonspecific clinical course of the disease, which is quite similar as other viroses, and rarely require hospital admission. Secondary transmission in families where the index case was a child is not uncommon and is also possible through contact with an asymptomatic child. After recovery, children have higher levels of antibodies at post-infection months 4 and 5.