It is happening. Israel is loosening the restrictions on movement. They are doing so based on planning and data, with guidelines as to how to measure if our efforts are safe and successful. As a society, the next milestone we are hoping to achieve is the reopening of schools. In this piece, I want to address where the scientific thinking is around the role of children (<18 years old) in the transmission of COVID-19 (corona).
Question 1: DO CHILDREN CATCH COVID-19?
Studies of the prevalence of COVID-19 in children find it between 1-5%. This means that for every 100 children tested, only 1 – 5 of them were positive for the virus. There are a few issues with this metric. Firstly, getting a good sample on a child is very challenging as they do not cooperate with the uncomfortable test. There is general agreement that we are missing some cases due to testing error. Secondly, there is testing bias. Most countries have been testing only those people with symptoms or close positive contacts, and children are generally asymptomatic, so possible positives are missed there. Iceland, however, has universal testing and published that 0 of the first 433 children tested were positive, which was interpreted as representing very low transmission among children. Based on these numbers, we assume the number of children who catch COVID19 may be 1 – 5% (possibly slightly more or maybe less).
Question 2: DO CHILDREN GET SICK ONCE INFECTED?
Children are showing much milder cases than adults. For example, in New York City, the rate of hospitalization for adults is 31 times higher than for children, and there have been five pediatric deaths versus >8,000 adult deaths so far. Children may be totally asymptomatic or present with cough, runny nose, and fever (general viral illness appearance). They much more rarely progress to pneumonia. In one Chinese paper of 171 pediatric cases, only one child died – an infant with previous severe congenital issues who was in the ICU already when he contracted COVID19. The older the child, the more like adults they present; some adolescents have been on ventilators in the ICU.
Question 3: DO CHILDREN TRANSMIT THE VIRUS?
So far, there are 57 research articles of varying quality which describe actual cases and chains of transmission involving children. We take these together to paint a picture of the role of children in the spread of the virus. For example, one very detailed report from France traced an infected 9-year-old boy as he went to school and had contact with 118 peers and community members. According to that contact-tracing, no one he encountered became sick. China and South Korea have published a number of papers describing chains of transmission. In all but one of them, children played no role in passing on the infection. The one case where a child may have transmitted the infection, was an infant to caretakers. In Norway, four adolescents appear to have transmitted the virus, but of the first 406 cases of infection chains investigated, none of them involved children. It is also notable that the vast majority of children who were found to be COVID19 positive caught it from their parents, not their community or school, according to the contact-tracing done.
Question 4: WHY DO CHILDREN NOT SEEM TO CATCH OR TRANSMIT COVID19?
If we only understood this! What we have observed is that how sick you become and how easily you transmit it seems to be correlated with how many viral units you have in your body (viral load). That is, imagine someone has one copy of the virus, they would not be able to transmit nor would be sick. Someone with 100 copies would be sick and could infect others. So one theory is that the virus does not replicate in the bodies of children well (maybe because they fight it off early) and so they have few copies. But there is evidence against this theory. The first pediatric case in Singapore (an infant infected by both his parents and his nanny), was a well baby (no previous conditions), who remained asymptomatic despite an extremely high viral load. So it may be more related to different expression of cells and bodies of children, or maybe related to fewer previous viral exposures and so a different immunological response to the virus.
Question 5: CAN WE SAFELY REOPEN SCHOOLS?
To summarize, transmission from young children to adults or other children is rare. The risk is not zero, but it appears to be low. More evidence on the impact of school reopening is coming. Denmark has been conducting a national experiment by reopening school last week for children younger than Grade 6. The Netherlands will do so in two weeks as well, and other nations are planning to follow suit.
One issue is that schools do not run on their own, and require adults to be in contact with each other in confined areas, so this would need to be addressed. A second is that even with low (but non-zero transmission), the emotional commitment of send your children out of the home on little evidence is big. For now, though, the data seems to suggest that reopening schools may be relatively low-risk for healthy young children (adolescents may be higher risk).