Children may transmit coronavirus at the same rate as adults: what we now know about schools and COVID-19

The latest research shows infections in children frequently go undetected, and that children are just as susceptible as adults to infection. Children likely transmit the virus at a similar rate to adults as well.

While children are thankfully much less likely than adults to get seriously ill, the same isn't true for the adults that care for them. Evidence suggests schools have been a driver of the second wave in Europe and elsewhere. This means the safety of schools needs an urgent rethink.

Infections with SARS-CoV-2, the virus that causes COVID-19, in children are generally much more mild than in adults and easy to overlook. A study from South Korea found the majority of children had symptoms mild enough to go unrecognised, and only 9 per cent were diagnosed at the time of symptom onset.

Researchers used an antibody test (which can detect if a person had the virus previously and recovered) to screen a representative sample of nearly 12,000 children from the general population in Germany. They found the majority of cases in children had been missed. In itself, that's not surprising, because many cases in adults are missed, too.

But what made this study important, was that it showed young and older children were similarly likely to have been infected.

Official testing in Germany had suggested young children were much less likely to be infected than teenagers, but this wasn't true. Younger children with infections just weren't getting tested. The study also found nearly half of infected children were asymptomatic. This is about twice what's typically seen in adults.

We've known for a while that around the same amount of viral genetic material can be found in the nose and throat of both children and adults.

But that doesn't necessarily mean children will transmit the same way adults do. Because children have a smaller lung capacity and are less likely to have symptoms, they might release less virus into the environment.

However, a new study conducted by the US Centers for Disease Control and Prevention (CDC) found children and adults were similarly likely to transmit the virus to their household contacts.

Another study, of more than 84,000 cases and their close contacts, in India found children and young adults were especially likely to transmit the virus.

Most of the children in these studies likely had symptoms. So, it's unclear if asymptomatic children transmit the virus in the same way.

But outbreaks in childcare centres have shown transmission by children who don't show symptoms still occurs. During an outbreak at two childcare centres in Utah, asymptomatic children transmitted the virus to their family members, which resulted in the hospitalisation of one parent.

Schools didn't appear to be a major driver of the epidemic in Victoria, although most students switched to remote learning around the peak of the second wave.

However, schools did contribute to community transmission to some extent. This was made clear by the Al-Taqwa College cluster, which was linked to outbreaks in Melbourne's public housing towers.

When researchers analysed cases in Victorian schools that occurred between the start of the epidemic and the end of August 2020, they found infections in schools mirrored what was happening in the community overall. They also found 66% of all infections in schools were limited to a single person.

This might seem encouraging, but we have to remember this virus is characterised by superspreading events. We now know that about 10% of infected people are responsible for about 80% of secondary COVID-19 cases.

Two major studies from Hong Kong and India revealed about 70% of people didn't transmit the virus to anyone. The problem, is the remainder can potentially infect a lot of people.

What happened in Victorian schools was entirely consistent with this.

The risk associated with schools rises with the level of community transmission. The picture internationally has made this clear.

After schools reopened in Montreal, Canada, school clusters quickly outnumbered those in workplaces and health-care settings combined. President of the Quebec Association of Infectious Disease Microbiologists, Karl Weiss, said, "Schools were the driver to start the second wave in Quebec, although the government did not recognise it."

A report by Israel's Ministry of Health concluded school reopening played at least some role in accelerating the epidemic there, and that schools may contribute to the spread of the virus unless community transmission is low. In the Czech Republic, a rapid surge in cases following the reopening of schools prompted the mayor of Prague to describe schools as "COVID trading exchanges".

The opposite pattern has been seen when schools have closed. England just witnessed a drop in new cases, followed by a return to growth, coinciding with the half-term school holidays. This was before any lockdown measures were introduced in the country.

These observations are consistent with a study examining the effect of imposing and lifting different restrictions in 131 countries. Researchers found school closures were associated with a reduction in R - the measure of how fast the virus is spreading - while reopening schools was associated with an increase.

The risk has been spelled out most clearly by the president of the Robert Koch Institute, Germany's equivalent of the US Centers for Disease Control and Prevention. Last week, he reported the virus is being carried into schools, and also back out into the community.

It won't be possible to control the pandemic if we don't fully address transmission by children. This means we need to take a proactive approach to schools.

At a minimum, precautionary measures should include the use of face masks by staff and students (including primary school students). Schools should also improve ventilation and indoor air quality, reduce class sizes, and ensure kids and staff practise hand hygiene.

School closures have a role to play as well. But they must be carefully considered because of the harms associated with them. But these harms are likely outweighed by the harms of an unmitigated epidemic.

In regions with high levels of community transmission, temporary school closures should be considered. While a lockdown without school closures can probably still reduce transmission, it is unlikely to be maximally effective.