Although there are some studies that suggest children do not transmit COVID, the vast majority are adding up to say differently. This is a thread to look at the pros and cons. A major confound is that studies choose different age groups to study ranging from 0 to 9, 14, 19, and 22 years. If we look at those over 10 years old, there is no question they transmit, and most studies say as much as adults. For younger children it is less clear but they likely transmit and there is no good reason why they would not.
On the side of those arguing children transmit.
1) Studies, blogs, threads, news articles used to show children transmit COVID-19 start the list. Those used by others to suggest children do not transmit are at the end. The exact answer is not clear, but it is certainly becoming clearer.
2) A good place to start reading is the thread by Zoe Hyde.
Zoe Hyde: https://threadreaderapp.com/thread/1312392762445066243.html
3) Another place are these by Sarah Rasmussen.
4) This review of 131 countries was in the Lancet and is one of the most convincing studies that children and schools can transmit and be drivers of the pandemic.
In a very large study in the journal Lancet on data from 131 countries to find the most important ways to reduce the spread of infection, several factors were examined, such as banning public events, closing workplaces, school closures, etc. It was investigated what happened to the R-value both when a restriction was introduced and what happened when this restriction was removed. The strongest effects of individual measures were obtained through a ban on public events (reduced R-value by 24%), removal of school closures (increased R-value by 24%) and abolition of a ban on large crowds (increased R-value by 25% ). From this analysis, you can also calculate how much the R-value changes on average if you combine different measures. So if a country, for example, imposes both a ban on larger crowds and a ban on public events, which resulted in a 29% reduction on average. More action in combination further reduces the R-value. This study can be used as a basis for decision-making, an idea of the effect of various limitations and what can be expected to happen when these are relieved.
5) This is a study looking at transmission by children 0-14 in two Indian states.
Young children often go undetected asymptomatic, but they transmit. “Kids are very efficient transmitters in this setting, which is something that hasn’t been firmly established in previous studies.”
An interesting aspect to this study is that they showed children 0-4 as index cases spread the virus very efficiently, especially to their own age group, which obviously can get infected. Of note, 0- to 4-year olds are a much smaller proportion of index cases than their proportion of the population as they very rarely get symptoms. So it is possible that children spread as efficiently in the rare cases where they do develop symptoms, but perhaps they don’t if they remain asymptomatic. We still do not know.
6) This is a summary from Smithsonian magazine, written in the summer, suggesting children transmit, but stating many questions still exist.
The data are from China, Korea, and the UK. Mostly groups of children from age 0 to 18 or 20. Study from Korea looked at 0-10 and found less transmitted. But all ages transmit.
7) This is a study out of S Korea. They found children < 10 transmitted less often to adults, those between 10 and 19 spread the virus as well as adults do. Households w the older children had highest spread compared to others.
8) In this study, they showed that opening elementary schools had limited impact on parents, but teachers in schools with older children had double the rate of infections compared with those who taught remotely. (Note, this study has also been used to argue children do not transmit).
9) In the United States, some high school reopenings have been disastrous, like those of a Georgia school shamed for unmasked students in its hallways and a high school in Utah where infections flared to 90 cases within two weeks.
10) There are case studies on young children too. This was a news article reporting a preschool infection in Stockholm.
11) This is a case study of transmission out of a preschool in Poland with children bringing the infection home.
12) This is a commentary and review by Zoe Hyde on Australian school data.
13) This is a recent case study from the CDC argues younger children are more infectious. “fourteen households in which the index patient was aged <18 years, secondary infection rate from patients aged <12 years was 53% and from patients aged 12–17 years was 38%.”
14) This is a recent news article stating that 50 Gothenburg, Sweden primary schools were infected this fall by November 6.
15) This is a story where epidemiologists state Montreal schools are driving the infection. This is aimed at teens as spreading.
16) Swedish data after the spring wave showed that children 0-19 have essentially as high seroprevelence as adults in Sweden by week 24 – see figure 2.
17) Finnish school situation report shows 5 of 6 infection trails in Helsinki come from schools.
18) Dutch study on children shows that they are infected. Does not track follow up infections.
19) Comprehensive study of infections in the UK. Secondary school age children have the highest levels.
20) And this set of UK data if you look at the charts show kids of all ages with positivity, and kids in secondary school are very high.
21) A study from a children’s hospital in Chicago, published in the Journal of the American Medical Association (JAMA), demonstrated that children spread the disease.
22) Another study from Italy showing transmission by children under 15.
23) The US Centers for Disease Control and Prevention (CDC) reported an outbreak in Georgia from June in a summer camp for children between the ages of 6 and 19. All participants had to present a Covid19-negative PCR test of maximum 12 days old. At the camp, the children, unlike the staff, did not have to wear face masks and the windows were not always open. The summer camp had to be canceled due to infection tracking and when 58 percent of the participants were tested, as many as 76 percent turned out to be positive for Covid-19.
24) An example from late spring / early summer. When Israel opened its schools in mid-July, the spread of infection increased markedly and many schools were forced to close again. This one has been challenged as other variables like releasing lockdown also occurred.
25) A new article by Zoe Hyde on children and transmission as well as schools as drivers in the second wave of the pandemic. “While children are thankfully much less likely than adults to get seriously ill, the same isn’t true for the adults that care for them. Evidence suggests schools have been a driver of the second wave in Europe and elsewhere. This means the safety of schools needs an urgent rethink.”
On studies that suggest that children are not infectious. We know now they get infected, just most have no symptoms.
1) This one argues school opening in UK did not correlate with cases.
2) This one is used by those arguing children do not transmit, but look at summary, “With good infection control measures, schools probably not more central arenas of infection than other arenas with a similar density of people.” And, it ONLY looks at cases. Children are less likely to show symptoms, so this is problematic.
3) This one from the NY Times says schools don’t drive the pandemic
But this one from the NY Times referring to the India study says they do
And the first article makes it clear that we really do not know. Headlines are deceiving.
4) This article refers to the seriously flawed Swedish study comparing to Finland that has met so much criticism in the press and then refers to the Isreali case study where schools were thought to drive the pandemic.
5) This one is often cited as defence that schools are not drivers, “We find that among parents, exposure to open rather than closed schools resulted in a small increase in PCR-confirmed infections [OR 1.15; CI95 1.03–1.27]. Among lower secondary teachers the infection rate doubled relative to upper secondary teachers [OR 2.01; CI95 1.52–2.67].” This could be used to support schools driving the pandemic, actually, and has been (see 8 above).
6) This is a very odd news article arguing children do not transmit. If you look at the papers referenced they are not all supportive of the citations.
The article leans heavily on the Italy study where schools were opened with community infections low in September, kids went back to school with a lot restrictions: masks except when sitting at spaced desks, good ventilation with large glass doors/windows open and warmer climate, no common materials, no physical contact. Right after this article, starting early October – one month after schools opened – community cases shot up!
7) Here is the Italian study and it says “only 2 %” of schools had outbreaks in the one month of September to October 5. But look at the numbers.
“As of 5 October 2020, a total of 1350 cases of SARS-CoV-2 infections have been registered in the Italian territory schools (involving 1059 students, 145 teachers and 146 other school members), for a total of 1212 out of 65104 (1.8%) Italian schools involved.” One has to wonder if you counted restaurants in Italy and compared to how many you can trace virus breakouts to, what the % would be? At a time that was low in community infection, 2% is a large number.
Infected students at the time were 7:1 over teachers, which makes sense as kids are more often asymptomatic. This is in line with expectations.
8) Another odd one to use for defence of schools, but it has been used for this. Check out fig 1 in the German data and schools closed versus open. Schools close, cases down, schools open cases up. Of course it was a lockdown so hard to judge here.
9) This USA study, used to say kids don’t transmit, is all about incidence and even states up front transmission can occur. But it is all PCR based and so mostly from children showing symptoms. Figures 2 suggests ages 5-11 have 40% incidence of ages 12-17 though so that is useful.
10) This meta analysis was cited in the nature news article as supporting the idea that kids don’t transmit. It has as a conclusion: “Data were insufficient to conclude whether transmission of SARS-CoV-2 by children is lower than by adults.” Again, incidence is lower. Also uses the flawed FHM data. Nothing from the comprehensive India or smaller Polish studies, etc. Mostly the older work from the spring. And Nature uses this as evidence children do not transmit.
Finally, here are comments on the Swedish report used to state schools and children do not drive infection. Looking at figures 1 and 2 in the report, the data and the y axes as well as when Finland closed its schools show infection rates higher in open Swedish schools than closed Finnish schools. And comparing teachers in Table 4 knowing that secondary school teachers were online and primary schools in person shows those on site had 60% higher case rate and averaged school data from the country side where infection was low overall.
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