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Even a year after the start of the pandemic, it’s still not entirely clear why this is the case. Research indicates a different immune response to viral exposure in children, which may mean that their immune system is able to neutralize the virus much faster and therefore prevents it from replicating. Children may also benefit from cross-protection by antibodies to other circulating coronaviruses to which they are more regularly exposed.
And it’s also possible that children have fewer ACE2 receptors in the cells that line the nasal passages, which are the gateways used by SARS-CoV-2 viruses to access. host cells and infect them. That would make it less likely for the virus to get a foot in the door. There is a more serious complication of exposure to SARS-CoV-2 that can occur in children called multisystem inflammatory syndrome in children, or MIS-C. However, it is rare, with fewer than 1,700 cases and only 26 deaths reported across the United States.
Children’s apparent resilience to covid-19 makes it a lower priority for immunization, especially when demand for vaccines far exceeds supply.
Children are also a challenge in vaccine development – and in any type of drug development – because they are viewed as a vulnerable population, says Beth Thielen, a pediatric infectious disease specialist at the University of Minnesota. “We want to take additional guarantees to protect them from injury,” she said. “We tend to be much more careful about enrolling children in education and not putting them at undue risk.”
The prospect that a trial of a new vaccine or drug in children outweighs the benefits is of particular concern when it comes to MIS-C, says Anna Sick-Samuels, pediatrician in the Division of Infectious Diseases at Johns Hopkins School of Medicine. MIS-C is believed to result from a massive inflammatory response to the SARS-CoV-2 virus. “It will be important to assess whether current RNA vaccines can lead to an antibody response that also triggers MIS-C or if it is just a complication of the viral infection,” she says.
It therefore seems likely that there will be a delay before children start to be immunized in large numbers. This means that there may be a demographic shift in covid-19 infections as older layers of the population gain immunity and the burden of infection shifts to younger, unvaccinated groups. This does not mean that more children will contract the virus, but if fewer adults are at risk, children will be overrepresented in the number of infections compared to adults – the opposite of what is currently seen in the world. .
This raises the possibility that postponing childhood immunizations could turn them into a reservoir of the virus in the population, which could continue to sow new outbreaks. This could be a problem even for vaccinated adults, says Mobeen Rathore, an infectious disease specialist and epidemiologist at the University of Florida College of Medicine.
Currently approved vaccines offer a high level of protection against infection, but not complete protection. In clinical trials, a small number of vaccinated adults were still infected, although they were much less likely to become seriously ill. There is also no data yet on whether vaccines prevent transmission from one vaccinated but infected person to another –although research is ongoing to find out if they do, and the start the signs are promising.
“So the question really is, these people who are vaccinated get the infection – they won’t get sick, but you won’t be able to stop the cycle of infection,” says Rathore. And as long as the virus is circulating in the population, there is a risk of disease, death and mutations.
Transmission issues
When the pandemic started, it was thought that children were less likely to pass SARS-CoV-2 to other children or to adults. A study of schools in England in June and July 2020, after they reopened after the first major lockdown, found relatively few infections or outbreaks. But other research, especially after schools, universities and colleges reopened, suggests infection rates are particularly high among young adults.
The evidence for transmission within and from younger age groups is conflicting, says Stefan Flasche, vaccine epidemiologist at the London School of Hygiene and Tropical Medicine. It’s complicated by the fact that infected children are also less likely to show symptoms than infected adults, which makes them less likely to get tested for the infection in the first place. “It looks like we are in a situation where children can transmit, but they are not the primary transmitters,” he says.
This could change once adults are vaccinated and therefore less likely to contract the disease. A similar development has already been seen in the UK, not as a result of vaccination but more recent lockdowns which have restricted movement of adults while schools remained open. “In this context, it appears that children were in fact the residual source of transmission or a substantial contributor to residual transmission,” says Flasche.
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