New York, Jun 5 (IANS): While kids were the least affected by the Covid-19 disease, a study suggests that 70.4 per cent of nearly 850,000 US household transmissions of SARS-CoV-2 virus originated with a child.

The study, published in JAMA Network Open, showed that younger children were more likely to spread the virus.

A team led by Boston Children's Hospital researchers gave smartphone-connected thermometers to 848,591 households with 1,391,095 members, who took 23,153,925 temperature readings from October 2019 to October 2022.

Fevers were a proxy for infection.

Among 166,170 households with both adult and child participants (51.9 per cent of households with multiple participants), there were 516,159 participants, 51.4 per cent of whom were children.

In these households, 38,787 transmissions occurred, 40.8 per cent of which were child to child, 29.6 per cent child to adult, 20.3 per cent adult to child, and 9.3 per cent adult to adult. The median serial interval between the index and secondary cases was two days.

Of all household transmissions, 70.4 per cent began with a child, with the proportion fluctuating weekly between 36.9 per cent and 87.5 per cent.

Children aged 8 years and younger were more likely to be the source of transmission than those aged 9 to 17 (7.6 per cent vs 5.8 per cent).

During most of the pandemic, the proportion of transmission from children was negatively correlated with new community Covid-19 cases.

"More than 70 per cent of transmissions in households with adults and children were from a paediatric index case, but this percentage fluctuated weekly," the researchers said.

"Once US schools reopened in fall 2020, children contributed more to inferred within-household transmission when they were in school, and less during summer and winter breaks, a pattern consistent for 2 consecutive school years."

The researchers said the finding that paediatric Covid-19 transmission was negatively correlated with new community cases during most of the pandemic is consistent with that of a previous study.

"When the incidence of Covid-19 increases, adults in the community are at higher risk of infection; this may increase the likelihood that adults become the index case in a household transmission and explain the negative correlation we observed," the researchers said.

"Also, when the Covid-19 incidence is low, overall use of nonpharmaceutical interventions might decrease, leading to increased incidence of non-SARS-CoV-2 pathogens which may be more common in children."

The team concluded that children had an important role in the spread of SARS-CoV-2 and that in-person schooling also resulted in substantial spread.