According to the researchers, the findings implied that with more exposure to the virus, children’s risk of becoming infected could substantially rise. Transmission of the virus within families was also a major factor, they said.

The results of the study – by researchers from two Shenzhen hospitals and the Southern University of Science and Technology – were published on Wednesday in the journal Emerging Infectious Diseases.

Meanwhile, another study, led by Qifang Bi at the Johns Hopkins Bloomberg School of Public Health in the US, found that among the close contacts of confirmed patients, there was no significant association between the probability of infection and age of the index case.

The study again looked at data from Shenzhen, in an epidemiology and transmission analysis of 391 cases and their 1,286 contacts. It found that among the close contacts of confirmed cases, 7.4 per cent of children under 10 were infected – almost the same as the average for all age groups of 7.9 per cent.

But it found that children who contracted the illness were less likely to have severe symptoms than other age groups. The researchers published their preprint paper on medRxiv, an online sharing resource for the medical and scientific communities.

Both studies suggested there was a risk of cluster transmission among children at home and in schools.

Dozens of affected countries, including Iran, Italy and Japan, have already ordered schools to shut. Others, such as South Korea, France, Germany, Singapore, Thailand, Britain and the United States, have introduced localised school closures.

However, health experts have observed that children seem to be less affected by the disease.

According to the official figures in China, only 965 cases – or 2.1 per cent of the total 44,672 confirmed cases by February 11 – were patients under the age of 20.

Of those, just 2.5 per cent had severe symptoms, and an even tinier proportion – 0.2 per cent – became critically ill. One teenager died from the disease in that period, and no deaths have been reported of children aged under nine worldwide.

But more research was needed to establish the infection rate of children, according to Keiji Fukuda, an epidemiologist at the University of Hong Kong.

It was not known whether there would be more illness in children, or whether the virus would spread more rapidly, within school clusters as this had not been properly studied, he said.

“We don’t really know what would have happened if children were exposed to a big dose of this thing in the school environment,” Aylward told reporters on Wednesday.

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Another possibility was that children were getting infected but they were not becoming very sick so they were not being identified as cases, Fukuda said.

If that was the case, it could mean children were playing a big role in spreading the virus, he said.

“We are going to probably need to do more … serologic studies [a type of blood test] on the population to get a better idea of what is the true infection rate of different age groups,” Fukuda said. “If children are getting infected, then they could be a major driver for how the infection spreads from person to person.”