A study in Clinical Infectious Diseases yesterday shows that children are unlikely to be the source of COVID-19 household outbreaks and are less likely to be infected with SARS-CoV-2 by another household member, with implications for vaccine distribution.
The role of children in the spread of SARS-CoV-2, the virus that causes COVID-19, has not been fully defined. While children typically have the highest rates of flu infection and are thought to play a major role in disease spread, scientists are still assessing data on their contribution to COVID-19 transmission.
A number of studies show low rates of pediatric SARS-CoV-2 infection and spread and mild symptoms in infected children, the study authors note. But they also point to studies that show that children shed virus at levels comparable to adults—suggesting that children could be a significant source of community transmission—with households thought to be one of the most common settings for transmission.
The researchers analyzed 57 studies published from Dec 1, 2019, to Aug 24, 2020, describing household transmission clusters in 12 countries. The studies identified index cases—individuals in the household who first developed symptoms—and measured the secondary attack rate (SAR)—the incidence of disease transmission to other members of the household.
Clusters were defined as a group of two or more confirmed infections in household members within 2 weeks of each other. Children were defined as anyone under 18 years old.
Only 4% of household clusters caused by children
The study authors found only 8 of 213 transmission clusters (3.8%) with a pediatric index case. Asymptomatic index cases were associated with a much lower SAR than symptomatic index cases (risk ratio [RR], 0.17; 95% CI, 0.09 to 0.29).
"Children may be less infectious than adults infected with SARS-CoV-2 due to their more mild clinical manifestation of disease," the authors wrote. "However, such a hypothesis requires validation across a larger and more diverse dataset."
Children were also less likely than adults to become infected by another member of the household (SAR risk ratio [RR], 0.62; 95% CI, 0.42 to 0.91) and were responsible for far fewer secondary cases than adult index cases—only 16 of 398. The small number of clusters with child index cases, however, precluded definitive conclusions.
While the data suggests that children may be less susceptible to SARS-CoV-2 infection than adults, the researchers cautioned that children may be infrequently identified as index cases because of limited interaction outside the home during the study period, a higher probability of adult travel to COVID-19–endemic areas, and datasets that include few children younger than 16 years old.
"These data should not be extrapolated to SARS-CoV-2 transmission outside the home where children tend to make more social contacts than adults," the authors cautioned.
Implications for vaccine priorities
If further research confirms the low likelihood of children as drivers of household COVID-19 transmission, vaccinating children first might not be an effective strategy for mitigating wider community spread.
"Whilst prioritising the vaccination [of] children against influenza has proved an effective tool in reducing the spread of influenza virus in the community, our data suggest that a similar strategy would be unlikely to significantly decrease the household transmission of SARS-CoV-2, the authors concluded.