SINGAPORE - The coronavirus disease Covid-19 does not appear to affect children as much as adults. The elderly and those with underlying conditions are most at risk of developing severe disease from Covid-19.

The Straits Times asked infectious disease expert Dale Fisher to shed light on the impact of the virus on children. Professor Fisher, the newly-appointed group director of medicine for National University Health System, is responsible for organising care for acute and chronic conditions in the cluster. He is also the chair of World Health Organisation's Global Outbreak Alert and Response Network.

Q: Why do children seem to be less affected by Covid-19 than adults?

A: We know there are other diseases where children aren't affected as much. For instance, chicken pox is a much milder illness for children than adults. And, a child with hepatitis A (a viral liver disease) probably doesn't have symptoms, but they can have antibodies if you test them, whereas adults with hepatitis A will go through fever and jaundice.

So we know that children and adults have different sorts of immune systems. The children could be - for reasons we don't yet understand - less likely to have symptoms.

If studies done to find out if children have antibodies to Covid-19 show that there are a lot of asymptomatic children, it will prove - but it won't tell us why - children are getting infected but not having symptoms.

Q: Should we worry about children passing Covid-19 to the elderly?

A: That's another question we don't yet know the answer to. However, if they are asymptomatic, they are unlikely to do so. In fact, a lot of the children that we have swabbed from family clusters showed that while the parents might have had the disease and had symptoms, the children are completely well even though they tested positive for it.

We've got no evidence that the child in those family clusters was the first person to get it. It's more the other way around - the parents have infected the child, the child's asymptomatic but you can find it on their throat. If you're asymptomatic, you're much less likely to spread it because you're not coughing, you're not making the droplets.

Is it theoretically possible to spread it if you share a pair of chopsticks, for instance? We think it's probably theoretically possible, but it's certainly not a major driver of the outbreak. The money is on people with symptoms spreading the disease before they're diagnosed and isolated. So if that period is a week, they are going to spread it a lot.

If it's two days, they won't spread it so much. If it's two days where they stayed home because they weren't feeling well, then they will spread to even fewer people or no one.