Advantages for kids comforting but mystifying
As young tend not to spread virus, opened schools seen unlikely to lead to more cases in new outbreaks
Data showing how children are largely being spared Covid-19 should give extra comfort to schools and kindergartens reopening today, an expert says.
But the pattern remains nonetheless puzzling to epidemiologists around the world.
New modelling has shown that, because children don’t tend to spread the disease or become severely ill, reopening schools would be unlikely to result in more cases if there were any outbreaks.
Looking at a hypothetical scenario in which schools had stayed open through the lockdown period, Te Pu¯naha Matatini researchers suggested that relaxing restrictions for children would have had only a small effect on the country’s total number of Covid-19 cases.
The modelling didn’t create a completely safe picture for schools: if reopening meant much more interaction between adults, such as at drop-off and pick-up time, then the risk of outbreak grew more likely.
But among children, the danger of transmission was low. Although one of New Zealand’s biggest Covid-19 clusters was named the Marist College cluster, that was because the first case was a teacher — and most cases didn’t involve children.
The modelling was partly based on new data reflecting how the disease was very different across age groups.
The probability of being “subclinical”, or generally without symptoms, for instance, was 80 per cent for people under 19, compared with just 20 per cent among those aged over 65.
With the exception of some tragic cases of young victims — yesterday’s sole new case was a boy aged under 4, and research has shown children with underlying health conditions face heightened risk — the trend was being seen around the world.
Otago University epidemiologist Professor Michael Baker said New Zealand’s numbers were too small to read too much into: “You’ve really got to look at a country that’s had a sustained epidemic — unfortunately, that’s now most of the world — and then ask, what’s the pattern after the virus is spreading widely?
“And what’s been very consistent is that children under 10 have much less illness.”
Baker cited a study from Iceland that randomly tested 12,232 people and found none of the 848 children under 10 tested positive, compared with 1 per cent of people older than 10.
Another study of residents of the Italian town of Vo also found no cases among children under 10, despite 86 per cent of the population having been infected.
In Chinese data from February, used in one recent review, children and adolescents accounted for just 2 per cent of Covid-19-related hospitalisations.
But the review also noted that, as kids were less frequently symptomatic and had fewer severe symptoms, they were less often tested, which could lead to an underestimate of the true numbers infected.
Also, children were less frequently exposed to the main sources of transmission of the virus.
Another report looking at 15 schools in New South Wales found only one primary school student and one high school student who may have contracted the virus from one initial case at their schools.
“It just seems that somehow, children’s immune systems are better at managing this infection,” Baker said.
“Not only are they not getting sick, they are seemingly unlikely to be detected. I’ve been reading about this immunity aspect and, although there are quite a few theories to explain it, basically, no one knows.
“I think that is very reassuring for schools, that their environments are relatively safe for children.”
To Baker, the low risk to children was one of the most fascinating mysteries about the pandemic, although he added it was common for kids and adults to experience infectious diseases differently.
“If we can work out what it is about children’s immune responses that is having an effect here, it might be key to developing vaccines or other strategies.”