70% of COVID-19 Cases Transmitted By Children


COVID-19, schools, and children are sensitive topics. Some worry about transmission in schools, while others don't see it as a concern. Which is it?

Children in school with masks on  (Adobe Stock, unknown)

Children in school with masks on

(Adobe Stock, unknown)

No one will disagree that emotions run high when one mentions COVID-19, schools, and children. On one side is a belief that schools pose a grave risk for COVID-19; on the other, it is not a major concern for schools and children.

This contention that schools should not be worried about COVID-19 was again questioned by a newly published article in Journal of American Medical Association Network, concluding that 70% of household transmissions were started with a child. The study found that children aged 8 and younger were more likely to be the transmission sources than those aged 9 to 17. None of this is a big surprise since early in 2020, a South Korean Study published in CDC’s Morbidity and Mortality Weekly Report found that children can spread the disease, and those aged 10 to 19 years spread it more commonly than adults. The common belief that these reports are disproven by the Swedish Experience is just disinformation. In December 2020 (last available data), the Publish Health Agency of Sweden reported that 75% of non-healthcare SARS-CoV-2 outbreaks originated in their elementary, grammar, and nursery schools.

The concern of teachers for their health is justified. Approximately 24% of teachers are at risk for severe COVID-19. A study from England and Wales found that primary school teachers were at the highest risk, being 67% more likely to develop SARS-CoV-2 infections than the average occupation.

Children can also be directly affected. Bloomberg reported in an interview with Daniel O. Griffin, MD, PhD, an infectious disease physician at Columbia University, that 5 to 10% of children who become infected can develop long-term symptoms. Pereira et al also reported in the Journal of Pediatrics that 12-16% of children infected with Omicron had long COVID at 3 and 6 months post-infection. In total 24% of children who are hospitalized have persistent symptoms greater than 5 months.

Similar to adults, the virus strikes multiple systems in children. As many as 60% of children have subclinical systolic cardiac impairment after recovery from asymptomatic or mildly symptomatic COVID-19 (average follow-up of 148 days). During the pandemic, the incidence of Type I diabetes in children almost doubled in those with a COVID-19 diagnosis (28.5 cases per 100,000 versus 55.2 cases per 100,000). There is also a risk of developing the rare but dangerous Multisystem inflammatory syndrome in children (MIS-C).

There is mounting evidence concerning immune hypofunction. The large surges of RSV infections seen in the United States were also seen in Sweden, a country that enacted little public health interventions, such as masking, and kept kindergartens and primary schools open. The Public Health Agency of Sweden also reported unusually severe influenza cases, stating that cases have occurred in “people under the age of 18 without underlying disease or condition, have been very seriously ill with complications such as myocarditis or encephalitis. (translated)”

Those who view COVID-19 as severely impacting children as rare are overlooking reinfections. Reinfections are all too familiar, as reported Amy Edwards, MD, (Associate Medical Director for Infection Control at University Hospitals Rainbow Babies & Children's Hospital) in the American Academy of Pediatric News. “A lot more kids are getting repeated COVID infections,” “It’s not unusual to see somebody get COVID in January, then in April and again in September. We often see that by that second or third infection, they develop long COVID. That, for me, is very concerning.”

Unfortunately, unlike adults, Pereira, et al also reported that the chances of developing long COVID in children do not appear to diminish with reinfections. This finding is supported by the research published in Clinical Immunology which found that, unlike adults, children did not develop robust memory (CD4+) T cells, placing them at risk for reinfections.

The good news is that much can be done to prevent and mitigate the above occurrences without the closures of schools. Multiple studies have shown masks to be effective in mitigating COVID-19-associated cases in schools. One study from Pima County, Arizona, found that schools without masking requirements were 3.5 times more likely to have COVID-19 outbreaks. Another study found that the increase in COVID-19 cases associated with school openings was more than halved in counties with school masking requirements (an increase of 16.32 cases per 100,000 residents versus 34.85 cases per 100,000 residents). Finally, a November 2022 study published in the New England Journal of Medicine reported that the lifting of masking requirements in the Greater Boston Area School District was associated with an additional 44.9 COVID-19 cases per 1000 students, 11,901 in total, which represented 29.4% of all cases at that time. The CDC has reported that during the Delta period, vaccinations cut adolescent hospitalizations by 90%. 

Two studies have described a multi-layered approach to opening schools. One from Switzerland reported the positive effects of masking and using air cleaners. Mask mandates decreased the detection of SARS-CoV-2 aerosols by 69%, and air cleaners decreased detected aerosols by 39%. This study also illustrates how masking can protect others, not just the wearer. In addition, the average indoor CO2 level was 1064, which is high, indicating that further decreases in aerosols might be obtained with further improvements in ventilation. Another study conducted during the pre-Delta and Omicron period found that the implementation of 7 or more mitigation strategies eliminated the increased risk of in-person school learning.

One of the lessons of the COVID-19 pandemic is that schools can be opened safely if proper mitigation strategies are in place. However, during the pandemic, we witnessed a vicious cycle of concerned and loving parents wanting in-person learning for their children but justifying their position by asserting that COVID-19 in children was “not a thing.” This often led to mitigation strategies not being implemented and teachers being reluctant to return to school. Schools remained closed for a period much longer than would have been necessary. We must start planning for the next infectious disease surge and build an effective school infrastructure, including upgrading ventilation and upper room UV-C germicidal lighting.

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