The Covid-19 puzzles that scientists are still trying to answer

The Observer’s science editor looks at questions such as why the disease does appear not to infect children, and whether men are really more susceptible

Robin McKie

Sat 14 Mar 2020 10.30 EDT Last modified on Wed 18 Mar 2020 06.55 EDT

A transmission electron microscope image shows SARS-CoV-2, the virus that causes COVID-19. Photograph: Alamy Stock Photo

Early on Saturday morning the news broke that a newborn baby had tested positive for coronavirus in a London hospital. The child is thought to be the youngest affected by the disease in the UK.

The child’s mother had been admitted to hospital days before the birth with suspected pneumonia. Tests – at North Middlesex hospital, in Edmonton – revealed she had the coronavirus. Then, minutes after she gave birth, her baby was given a test which was also positive for Covid-19. It is not known whether the child contracted the disease in the womb or was infected during birth.

The case is striking because generally Covid-19 has had very little impact on children or young adults. The Chinese Centres for Disease Control and Prevention said its analysis, released on 11 February, of just under 45,000 cases revealed that less than 1% were under nine years old, while those aged between 10 and 19 accounted for just over 1%. By contrast, those aged between 50 and 59 made up almost 25% of the cases while those between 60 and 69 made up 19%.

“The information suggests that children are less likely to be infected than adults and that is a bit of a puzzle,” says Professor Jimmy Whitworth, of the London School of Hygiene & Tropical Medicine.

One suggestion put forward by researchers is that children have upper-respiratory tract illnesses most of the time. “It may be that they are simply not reporting themselves as feeling ill,” adds Whitworth. “So they are not getting tested. It could be just a sampling issue.”

Alternatively, it is possible that other human coronaviruses – which are known to cause minor colds – may be circulating in schools and playgrounds and these could providing a degree of cross protection against Covid-19. “Or it could be something to do with social mixing,” says Whitworth. “We know children interact mostly with other children and adults mostly interact with adults. It is not as though the whole of society mixes randomly. So those differential mixing patterns might explain part of it.”

The low numbers of Covid-19 infections among children is not the only mystery. It has been known to science for only a few months and many of its features continue to puzzle experts. One of these concerns hypertension – high blood pressure. Studies of Chinese cases suggest that adults with high blood pressure are more at risk of dying from coronavirus than others.

Again scientists find it difficult to find simple explanations. “It may be such individuals have other conditions that have not been recognised,” says Tom Wingfield, a clinician at Liverpool School of Tropical Medicine. “We know that people with hypertension are more likely to be diabetic and have impaired kidneys, for example. That could be a factor but the honest answer is that we just do not know at present.”

Other puzzles about the impact of Covid-19 have simpler explanations, however. For example, there is its tendency to kill men more often than women. The infection is fatal for 4.7% of men, but just 2.8 % of women, even though the gender balance for those testing positive is roughly 50:50.

Most experts say this is explained by the fact that in China smoking is primarily a male prerogative and this has weakened men’s respiratory systems and made them more vulnerable to Covid-19.

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