When officials closed U.S. schools in March to limit the spread of COVID-19, they may have prevented more than 1 million cases over a 26-day period, a new estimate published online July 29 in JAMA suggests.
But school closures also left blind spots in understanding how children and schools affect disease transmission.
“School closures early in pandemic responses thwarted larger-scale investigations of schools as a source of community transmission,” researchers noted in a separate study, published online July 30 in JAMA Pediatrics, that examined levels of viral RNA in children and adults with COVID-19.
“Our analyses suggest children younger than 5 years with mild to moderate COVID-19 have high amounts of SARS-CoV-2 viral RNA in their nasopharynx, compared with older children and adults,” reported Taylor Heald-Sargent, MD, PhD, and colleagues. “Thus, young children can potentially be important drivers of SARS-CoV-2 spread in the general population, as has been demonstrated with respiratory syncytial virus, where children with high viral loads are more likely to transmit.”
Although the study “was not designed to prove that younger children spread COVID-19 as much as adults,” it is a possibility, Dr. Heald-Sargent, a pediatric infectious diseases specialist at Ann and Robert H. Lurie Children’s Hospital and assistant professor of pediatrics at Northwestern University, Chicago, said in a related news release. “We need to take that into account in efforts to reduce transmission as we continue to learn more about this virus.”.
The study included 145 patients with mild or moderate illness who were within 1 week of symptom onset. The researchers used reverse transcriptase–polymerase chain reaction (rt-PCR) on nasopharyngeal swabs collected at inpatient, outpatient, emergency department, or drive-through testing sites to measure SARS-CoV-2 levels. The investigators compared PCR amplification cycle threshold (CT) values for children younger than 5 years (n = 46), children aged 5-17 years (n = 51), and adults aged 18-65 years (n = 48); lower CT values indicate higher amounts of viral nucleic acid.
Median CT values for older children and adults were similar (about 11), whereas the median CT value for young children was significantly lower (6.5). The differences between young children and adults “approximate a 10-fold to 100-fold greater amount of SARS-CoV-2 in the upper respiratory tract of young children,” the researchers wrote.
“Behavioral habits of young children and close quarters in school and day care settings raise concern for SARS-CoV-2 amplification in this population as public health restrictions are eased,” they write.
Modeling the impact of school closures
In the JAMA study, Katherine A. Auger, MD, of Cincinnati Children’s Hospital Medical Center, and colleagues examined at the U.S. population level whether closing schools, as all 50 states did in March, was associated with relative decreases in COVID-19 incidence and mortality.
To isolate the effect of school closures, the researchers used an interrupted time series analysis and included other state-level nonpharmaceutical interventions and variables in their regression models.
“Per week, the incidence was estimated to have been 39% of what it would have been had schools remained open,” Dr. Auger and colleagues wrote. “Extrapolating the absolute differences of 423.9 cases and 12.6 deaths per 100,000 to 322.2 million residents nationally suggests that school closure may have been associated with approximately 1.37 million fewer cases of COVID-19 over a 26-day period and 40,600 fewer deaths over a 16-day period; however, these figures do not account for uncertainty in the model assumptions and the resulting estimates.”
Relative reductions in incidence and mortality were largest in states that closed schools when the incidence of COVID-19 was low, the authors found.