First, the risk from the initial covid-19 disease itself. According to CDC data, kids under 15 are more likely to die from the flu than from covid. For older age groups, covid is much, much worse than the flu. Just for funsies, here is that CDC data put into a graphical form. We know at this point that the official data is not fantastic, but I think it's okay for a comparison of this kind, to show the age effect.
Because kids have such mild symptoms, they are much less likely than adults to be diagnosed. There have been a few studies that try to determine whether or not kids are less likely to get the virus if exposed. The difficulty is that it's hard to know how much someone was exposed. There are two similar studies, both done in China, that came up with different results. The general idea is to follow secondary contacts of infected people -- mostly people living in the same household. If one person in the household is diagnosed, who else in the same household gets it? The first study found that kids were just as likely as adults to get the virus, the second one found that they were less likely to get it. One explanation may be that early on, we didn't know about the potential for the secondary inflammatory disease in kids, so parents didn't worry about exposing their kids, but later on, they might have changed their behavior to prevent transmission to their kids.
There was also a study in Belgium, right before the lockdown there, in which kids in daycare centers were screened for the virus. No cases were found, despite lots of the kids having colds. An antibody screening study in Switzerland found that both kids and older people were less likely to have antibodies. I think that this suggests that people are protecting groups they see as vulnerable from exposure, but again, it's not definitive.
So the upshot so far is that while kids are clearly much less likely to have severe cases, I'm not convinced that they are less likely to be infected. It's certainly possible, but not definitive.
Turning now to Kawasaki Disease / post-covid inflammatory syndrome, various hospitals have noted a sudden increase in the number of kids coming in with symptoms of severe inflammation. In some kids, it manifests in the heart, others have severe skin rashes, GI symptoms are common. This paper reports a 13-fold increase in this syndrome at a hospital in Paris. Most of the kids had a positive antibody or PCR test for covid.
So how common is this syndrome in kids that become infected? We can try to get a rough estimate based on the Paris report. The background prevalence of Kawasaki disease in northern France is 9 per 100,000 kids under 5, and typically about 3/4 of the cases are in kids under 5, so overall prevalence is about 11 per 100,000. So we might expect (11 x 13 = 143, minus 11 background is 132 out of 100,000 additional cases in a population that had the same infection rate as the kids in Paris. This news site reports that about 10% of Paris area kids tested positive for antibodies. So if all kids were infected, that would be 1320 per 100,000, or 1.3%. If that's real, it would be a solid nope from me, given the severity of symptoms mentioned in the Paris paper. It describes kids having lumbar punctures and exploratory surgery to try to figure out what was going on with them.
Just to check another region, here is a study from Bergamo, Italy, in which the incidence of Kawasaki disease increased 30-fold. Background prevalence of KD in Italy is about 22 per 100,000. So 22 x 30 = 660, subtract out the 22 background to get 638 per 100,000. I can't find info on antibodies in kids specifically, but about half the population of Bergamo overall had antibodies. If that holds for kids, that would be 638 x 2 = 1276 out of 100,000 or 1.3%.
In both of these cases, the antibodies were measuring the whole outbreak, and the KD increases were measured over just a short period of time, so it's not the best comparison. So take this as a rough estimate, even though I came up with the same number in two different cities.
I know people are eager for life to get back to normal, but subjecting kids to a virus that has nasty after-effects in 1 in 100 sounds like a bad idea to me. If anyone has better data on the percent of kids who have the inflammatory syndrome / Kawasaki disease after contracting SARS CoV-2, please do share.
There was also a study in Belgium, right before the lockdown there, in which kids in daycare centers were screened for the virus. No cases were found, despite lots of the kids having colds. An antibody screening study in Switzerland found that both kids and older people were less likely to have antibodies. I think that this suggests that people are protecting groups they see as vulnerable from exposure, but again, it's not definitive.
So the upshot so far is that while kids are clearly much less likely to have severe cases, I'm not convinced that they are less likely to be infected. It's certainly possible, but not definitive.
Turning now to Kawasaki Disease / post-covid inflammatory syndrome, various hospitals have noted a sudden increase in the number of kids coming in with symptoms of severe inflammation. In some kids, it manifests in the heart, others have severe skin rashes, GI symptoms are common. This paper reports a 13-fold increase in this syndrome at a hospital in Paris. Most of the kids had a positive antibody or PCR test for covid.
So how common is this syndrome in kids that become infected? We can try to get a rough estimate based on the Paris report. The background prevalence of Kawasaki disease in northern France is 9 per 100,000 kids under 5, and typically about 3/4 of the cases are in kids under 5, so overall prevalence is about 11 per 100,000. So we might expect (11 x 13 = 143, minus 11 background is 132 out of 100,000 additional cases in a population that had the same infection rate as the kids in Paris. This news site reports that about 10% of Paris area kids tested positive for antibodies. So if all kids were infected, that would be 1320 per 100,000, or 1.3%. If that's real, it would be a solid nope from me, given the severity of symptoms mentioned in the Paris paper. It describes kids having lumbar punctures and exploratory surgery to try to figure out what was going on with them.
Just to check another region, here is a study from Bergamo, Italy, in which the incidence of Kawasaki disease increased 30-fold. Background prevalence of KD in Italy is about 22 per 100,000. So 22 x 30 = 660, subtract out the 22 background to get 638 per 100,000. I can't find info on antibodies in kids specifically, but about half the population of Bergamo overall had antibodies. If that holds for kids, that would be 638 x 2 = 1276 out of 100,000 or 1.3%.
In both of these cases, the antibodies were measuring the whole outbreak, and the KD increases were measured over just a short period of time, so it's not the best comparison. So take this as a rough estimate, even though I came up with the same number in two different cities.
I know people are eager for life to get back to normal, but subjecting kids to a virus that has nasty after-effects in 1 in 100 sounds like a bad idea to me. If anyone has better data on the percent of kids who have the inflammatory syndrome / Kawasaki disease after contracting SARS CoV-2, please do share.
