Symptomless cases in schools could be key driver in spread of Covid-19

Up to 70% of schoolchildren infected with coronavirus may not know they have it until after a positive test result

A key factor in the spread of Covid-19 in schools is symptomless cases. Most scientists believe that between 30% and 40% of adults do not display any Covid symptoms on the day of testing, even if they have been infected. For children, however, this figure is higher.

“It is probably more like 50% for those in secondary school while for boys and girls in primary school, around 70% may not be displaying symptoms even though they have picked up the virus,” says Professor Martin Hibberd of the London School of Hygiene and Tropical Medicine.

That is a large proportion of symptom-free disease-carriers within a population. What is not yet known is just how much infection is being passed on by this cohort of young symptom-free carriers. It is a critically important issue, and one that will play a key role in determining the effect of Covid-19 on the people of Britain in the next few weeks, say researchers.

Unfortunately a definitive answer on the infectiousness of young people remains tantalisingly out of reach, although there is evidence to suggest that people who don’t display symptoms of Covid-19 may have lower viral loads, which means they are less likely to infect others.

This tendency correlates with age, so younger children have lower viral loads. As a result, they are less likely to display symptoms – and also less likely to pass on the virus. “It’s a real possibility but we cannot yet be sure,” says Hibberd.

One solution to the problem is to increase testing in schools. This would require the widespread deployment of rapid testing, particularly with the lateral flow method, which is easily administered and gives results in less than half an hour. It is less accurate than the standard PCR swab test, however, and there have been concerns about a high level of false negative results leading to the continued spread of the new, more infectious, variant of the coronavirus.

However, scientists point out that rapid tests are better at spotting individuals with high viral loads than those with lower ones.

“We know that a high viral load is a key issue affecting the virus’s transmission, so even if we can’t detect every carrier, we are most likely to pick up those children who are more likely to transmit,” says Hibberd.

“And frequent testing using other technologies – such as isothermal amplification (Lamp) testing – could further reduce the rate of false negatives. However, we have to be sure that we have a competent testing system in place in schools before we can be sure of that.”

• This article was amended on 3 January 2021 to correct the first name of Professor Hibberd; he is Martin, not Michael as an earlier version said.


Robin McKie Science editor

The GuardianTramp

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