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Based on a comprehensive analysis of the chains of infection, children could play a larger role in the spread of the coronavirus than previous research suggested. Furthermore, apparently only a fraction of those infected transmit the virus, reports an international research team in the journal “Science.”
For the analysis, the scientists evaluated data from more than 570,000 people of all ages who were exposed to the coronavirus because someone in their vicinity was infected. The most important results at a glance:
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Seventy percent of those infected apparently did not transmit the virus at all.. In contrast, more than half of the new infections recorded traced back to just eight percent of those originally infected; they acted as the so-called super spreaders.
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The infected children transmitted the virus primarily to their peers, according to the data. Nearly one in four children between the ages of one and four becomes infected when they come in contact with an infected child. In the 5-17 age group, it was still one in five. “Children are very efficient vectors, which has not been shown in previous studies,” said study author Ramanan Laxminarayan of Princeton University. Adults, on the other hand, apparently infect children much less frequently, here the value was between five and eight percent.
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In general the Probability of getting infected between 2.6 and nine percent. The risk was higher when those affected lived together in the same home.
The role of children in the pandemic has been investigated since the beginning of the pandemic. It is clear that they are significantly less likely to develop Covid-19 than adults. However, the extent to which they transmit the virus is controversial. In the case of other infectious diseases like the flu, children are considered drivers. Is that also the case for Corona? Some studies suggest it, others against it.
The current analysis cannot completely clarify this contradiction either. Contact tracing studies are time consuming. And it’s not always possible to reconstruct who got infected first. Mainly because people without symptoms can probably also be contagious. The researchers suspect that children are therefore rarely recognized as index patients. Only 64 of the more than 1,300 index patients for whom the test results of their contact persons were available were children. Its role in the pandemic could be underestimated, the research team writes.
The second important finding of the study was more evident in the data than in the children’s role: the importance of overlapping events. The deciding factor here is probably not the infected person themselves, but the circumstances in which they come into contact with other people. “Super spread events are more the rule than the exception when looking at the spread of Covid-19 in India and probably all other affected areas as well,” says Laxminarayan.
“The largest empirical demonstration of superpropagation that we know of for any infectious disease”
To assess the role of individual outbreaks in a pandemic, epidemiologists use the so-called spread factor or dispersion parameter k. Describe how much the number of infected people varies. The lower k is, the more infections can be traced to one or a few situations: so-called superprocessor events. In this case, a pandemic does not spread evenly, but in large individual outbreaks.
The pathogen Sars, which is closely related to the coronavirus, is known to barely transmit the virus to nearly three-quarters of those infected. Therefore, experts estimate that the dispersion factor k in Sars is around 0.16, a particularly low value. Virologist Christian Drosten assumes that Sars-CoV-2 will also spread mainly in groups; This can be a family celebration or a shared apartment.
If these clusters go undetected, there may come a point where the number of cases spikes again suddenly and rapidly for no apparent reason. “We don’t even know what’s changed, but it’s getting more and more,” Drosten said, describing the situation on the NDR podcast in early September. This could also explain the rapid increase in the number of cases in countries like France. “Our study,” says study author Laxminarayan, “is the largest empirical demonstration of superpropagation that we know of for any infectious disease.”
