SINGAPORE - Those below the age of 16 will not be getting the Covid-19 vaccination any time soon because not enough is known about side effects in this group. Children and young people have a much lower risk of contracting the virus, and studies have shown that they are less likely to be active spreaders of it too.

Here is what we know so far:

Q: Why are younger children less likely to be infected with Covid-19 compared with older children?

A: There are many possible reasons for this.

Dr Yung Chee Fu, a consultant at the KK Women's and Children's Hospital (KKH)'s Infectious Diseases Service, said that one possible explanation could be a lower expression of the angiotensin-converting enzyme 2 (ACE2) receptors in younger children. These enzyme receptors are the Sars-CoV-2 virus' entry points into body cells.

As such, younger children up to the age of four had the lowest rates of infection at 1.3 per cent, according to a study conducted by KKH among 137 households between March and April last year.

Professor Paul Tambyah, a senior consultant at the Division of Infectious Diseases at the National University Hospital, said that the exposure to multiple common colds at different ages could allow children to confer protection from seasonal coronaviruses, such as Covid-19.

"Young children get colds all the time, so when they are in early primary school, they have antibodies which protect them from getting colds as often as they used to in kindergarten or nursery.

"Some of those antibodies may protect them from infections of the Sars-CoV-2 virus, and this may explain why young children don't get severe Covid-19. It is also possible that these antibodies may decline with time, which is perhaps why older people are more vulnerable," he said.

In addition, the maturation of one's immune cells at different ages could lead to differences in immune response to the virus.

Q: What kind of treatment is provided to children who have tested positive for Covid-19?

A: Dr Mohana Rajakulendran, a paediatrician at the Parkway East Hospital, said that as the majority of children who are positive for Covid-19 have mild symptoms, their symptoms are treated with fever, cough or cold medications.

They are closely monitored for complications such as pneumonia, which may require oxygen support or poor feeding, which may require fluid support through intravenous hydration.

So far, there have been no reported cases in children of Kawasaki disease associated with Covid-19, which is a severe form of inflammatory disease caused by an overreaction of one's immune system.

Q: Given the recent news that there were two confirmed cases of Raffles Girls' School students with Covid-19, should we be wary of a possible school-related outbreak?

A: School-related outbreaks in Singapore are unlikely, given that the children's ability to infect others and their ability to be infected is relatively low. In addition, safe management measures in schools such as social distancing, compulsory mask-wearing and temperature taking, can also help to prevent the spread of the virus.

A household transmission study conducted by KKH among 137 households exposed to Covid-19 found that there were 13 confirmed cases of Covid-19 among children, revealing an adult-to-child transmission rate of around 6 per cent.

Prof Tambyah said: "Unlike with influenza, children are unlikely to be the main drivers of infection. There may be some silent transmission from asymptomatic children, but this is likely to be insignificant in the big picture.

"As such, infection control efforts in pre-schools and primary schools could potentially be more relaxed than in tertiary settings - if the current data can be validated in large prospective studies."

Similarly, an Icelandic study published by the National Geographic on Dec 10 found that children under the age of 15 were around half as likely as adults to be infected and to transmit the virus to others.

The study, which was conducted among 40,000 people, also found that almost all the coronavirus transmissions to children came from adults.

The findings were consistent with the situation in Singapore, where children who were asymptomatic but tested positive for Covid-19 were often household contacts of infected adult family members. The children were swabbed as part of contact tracing measures and were not identified as index cases for spread.

Q: Given that most of the children who had tested positive for Covid-19 exhibited mild symptoms or were asymptomatic, what are the wider implications for infection control?

A: Taking all the evidence into account, Prof Tambyah said that Covid-19 vaccines should be targeted at adults instead of children, given that it is more likely for adults to be the primary drivers of transmission.

He noted that in Japan, children, who are the primary transmitters of influenza, were vaccinated to prevent infecting their grandparents, who were identified as vulnerable segments of the population. This helped to achieve herd immunity.

In addition, screening children for symptoms when they are coming into contact with vulnerable people such as the elderly should also focus on their household contacts.

For example, if a children's group is going to visit a senior home, it is more important to find out if their parents had shown any flu-like symptoms in recent weeks, instead of just screening the children who may be asymptomatic.