As ministers and teachers wrestle with the challenge of safely opening schools in England in September, a former government adviser, Neil Ferguson, threw another spanner in the works by suggesting older teenagers could transmit the virus as well as adults.
Ferguson told BBC Radio 4’s Today programme: “The risk then is that big schools, comprehensives, universities, FE [further education] colleges link lots of households together, reconnect the social network, which social distancing measures have deliberately disconnected. And that poses a real risk of amplification of transmission, of case numbers going up quite sharply.”
A South Korean study published in a Centers for Disease Control and Prevention journal last month found Covid infection rates among household contacts to be highest where they resided with someone with the virus in the 10- to 19-year-old age group. By contrast, they were lowest in the 0-10 age group.
Dr Simon Clarke, associate professor of cellular microbiology at the University of Reading, said of the study: “It’s the best we’ve got. Children get the virus at all sorts of ages. Because people haven’t been at school, there’s no real epidemiological evidence for whether it’s a problem or not.”
Another study, published in June, found “the added return of most (primarily older) students in Germany has increased transmission among students, but not staff. It is unclear whether older students transmit more, or if physical distancing is practically unfeasible in classrooms at high capacity.”
However, the same phenomenon was not observed in Denmark and Norway, countries with lower community transmission than Germany, the study found. The picture is further complicated by research that found that children under five with mild to moderate Covid-19 have a much higher viral load.
Paul Hunter, professor in medicine at the University of East Anglia, said: “My best guess is that an infected young child is more infectious but teenagers have many more close contacts and so are more likely to spread the infection.
“If you look at Sweden, that country kept its primary schools open but closed its secondary schools and higher education institutions. So maybe that was enough to suppress the R value a bit.”
Several experts suggest greater social contact might explain older children being more likely to spread the virus than their younger counterparts. However, Dr Sarah Lewis, senior lecturer in genetic epidemiology at the University of Bristol, said: “This could also be due to different immune mechanisms among younger children.”
A Public Health England (PHE) source said the risk cited by Ferguson was “very much our understanding”. They added: “It means that we are going to have to be careful about the reopening. Overall, though, we must really bear in mind the harms caused to children by not going back to school and, at a population scale, this may well be much larger than that of Covid.”
It highlights why the government’s advisers on the Scientific Advisory Group for Emergencies (Sage) have been trumpeting the importance of a robust test-and-trace system and continued social distancing if the return of children to school is not to cause a surge in new Covid cases.