Children were less likely than adults to acquire a COVID-19 infection from an index case, a meta-analysis found.

Across 32 contact tracing or population testing studies comparing SARS-CoV-2 prevalence in children and adults, children younger than 14 were less likely to be infected from an index case overall (odds ratio 0.56, 95% CI 0.37-0.85), and specifically in studies examining household transmission (OR 0.41, 95% CI 0.22-0.76), reported Russell M. Viner, PhD, of the UCL Great Ormond Street Institute of Child Health in London, and colleagues.

However, adolescents 14 and older did not have a significantly lower risk of infection compared with adults (OR 1.23, 95% CI 0.64-2.36), they wrote in JAMA Pediatrics.

Seroprevalence appeared to be lower in children than adults, especially for children younger than 14, who had 48% lower odds of infection compared with young adults 20 and over, they reported.

While “we found few data that were informative on the onward transmission of SARS-CoV-2 from children to others,” the findings suggest “children and adolescents have less opportunity for onward transmission,” Viner and co-authors noted.

Children tend to be less vulnerable to serious complications of COVID-19 than adults, but a recent CDC analysis demonstrated that the median age of coronavirus patients is trending downward, with people in their 20s accounting for more than one in five infections reported from June to August.

Although school closures may have impacted the extent to which transmission was occurring among children in many of these studies, “it is important that children have similar or lower seroprevalence than elderly individuals, despite higher levels of household exposure to infected contacts,” commented Saul N. Faust, MD, PhD, and Alasdair P. S. Munro, MD, of the University of Southampton in England, in an accompanying editorial.

But how easily children spread the virus once they are infected remains unclear. Research has shown that children can have relatively high viral loads compared with adults, but that does not necessarily mean they are spreading the disease more.

Whether adults are infecting children or vice versa is “hard to investigate in a disease where the true proportions of asymptomatic infection according to age remains unknown,” Faust and Munro noted.

While studies among schoolchildren in Australia, Singapore, and Ireland have “generally been reassuring,” studies of older children in France and Israel have also demonstrated “outbreak potential,” they explained.

Interpreting these data is challenging because it is still unclear which direction the virus is spreading since “it has been impossible to determine the relative proportion of teacher (adult)-to-child spread compared with child-to-child spread,” the editorialists wrote.

In three studies examining school data, transmission appeared relatively low. For example, in a population-based Australian study conducted before and during school closures, a majority of index cases were among staff, with no evidence of child-to-adult transmission, and an overall secondary attack rate of 1.2%. Similarly, data from Ireland and Singapore before school closures demonstrated “very few” secondary cases in schools, Viner and co-authors reported.

With all of the unknowns, governments should consider community transmission; a school’s capacity to provide socially and culturally competent infection prevention measures; and the needs and wants of children and families when considering reopening, Faust and Munro said.

“It is not so simple as to say that children are not affected and cannot transmit, nor to say that schools should be closed or risk near certainty of propagating a second wave of infections,” they wrote. “The education and well-being of the current generation of children and young people should be the highest priority in any national strategy to reopen society.”

For this analysis, the authors pooled studies comparing SARS-CoV-2 infection, confirmed by polymerase chain reaction (PCR) tests or serology, among children and adults at a population level. Single household or center studies were excluded, as were studies of hospitalized patients. Preprint studies were included.

In total, the 32 studies pooled data from 41,640 children and 268,945 adults globally. Eighteen studies used contact tracing data, with three in schools, and 14 used population testing. Because populations differed widely across the 21 countries in which the studies took place, a meta-analysis was not performed among the population testing studies, researchers noted.

The low quality of some included studies and the possibility of bias are limitations, the authors noted. A low infection rate in some contact tracing studies may also represent an underestimate of unmitigated household transmission, they added. The population testing studies also included a low proportion of children, which may be a source of bias, they wrote.

“We remain early in the COVID-19 pandemic, and data continue to evolve,” Viner and co-authors wrote. “It is possible that unknown factors related to age, [like] transience of infection or waning of immunity, bias findings in ways we do not yet understand.”