Children are about half as susceptible as adults to contracting COVID-19, according to new research from Israel.
Children in households where someone had coronavirus disease 2019 (COVID-19) were about about half as likely to test positive for the disease as adults, according to a new study, which also found children to be less likely to pass the disease on to others.
The study, published in PLOS Computational Biology, examined data from 637 households in Bnei Brak, Israel, including 3,353 individuals to analyze the susceptibility and infectivity of children compared with adults. Among the households included in the study, at least one member tested positive for COVID-19. Excluding these index cases, 25% of children and 44% of adults tested positive for COVID-19.
“Our research provides evidence that the susceptibility of children to infection with SARS-CoV-2 is significantly lower than that of adults (approximately by half),” Yair Goldberg, PhD, associate professor, at the Faculty of Industrial Engineering & Management at Technion Israel Institute of Technology told Contagion®. “We also estimated somewhat lower infectivity for children who are infected, though results are less clear-cut in this regard.”
PCR testing determined that 1,510 of 3,353 household members were positive for COVID-19. The study found that susceptibility to COVID-19 among children younger than 20 was 43% (95% CI: [31%, 55%]) of the susceptibility of adults and infectivity of children was 63% (95% CI: [37%, 88%]) of infectivity of adults.
The study found that the odds of testing positive for COVID-19 increased with age until about age 20 and remained constant thereafter.
“When we looked at the data we were surprised by the fact that the chance for a child to have been tested positive increased with the age of the child,” Goldberg said. “We were also surprised by the large percentage of infected people in the families we studied (45%).”
Data from serological testing among a subset of participants and PCR testing showed that infections are under-detected and that is more substantial among children.
That difference was expected based on previous findings that children are more likely to have mild or no symptoms. For example, one recent study in the Canadian Medical Association Journal found that about 36% of children who tested positive for COVID-19 were asymptomatic.
However, the difference in under-detection isn’t significant enough to explain the difference in positivity rates between children and adults. Even after adjusting for under-detection, the data still showed lower infections rates for children.
“While there is now good evidence that children are less susceptible to infection than adults when exposed to infected people, and it is clear that children display milder symptoms when infected, it should be kept in mind that transmission is context-dependent and that higher contact rates among children in settings such as schools can offset the effect of lower susceptibility and lead to outbreaks,” Goldberg said. “Therefore, efforts must still be made to protect children, in particular since currently they are not vaccinated.”
Some have feared that COVID-19 may become more severe among children over time. So far that doesn’t seem to be the case, according to one study, that found that the proportions of deaths caused by COVID-19 in children was stable across May, June and July.
More research is needed to better understand the factors that affect transmission along with the role of children in spreading the disease as the pandemic evolves.
“It is important to evaluate the effect of new strains on transmission,” Goldberg said. “While there is strong evidence that new strains are more transmissible, it is not clear whether they change the picture regarding the lower relative susceptibility of children. This an issue that needs to be investigated in the future and household studies such as ours are one useful way to do so.”