A simulation study of Covid-19 transmission in elementary and high schools suggested that schools can safely reopen for in-person learning… assuming community transmission is controlled and rigorous mitigation efforts, including asymptomatic screening and schedule changes, can be maintained.
After nationwide school closures during the height of the Covid-19 pandemic in 2020, schools across the U.S. have begun to reopen classrooms. As of June 2021, 80% to 100% of kindergarten through 12th grade (K-12) students in most states have been offered the opportunity to shift from online to in-person learning, but many families that are offered opt to keep their children at home rather than risk infection at school, Meagan C. Fitzpatrick, PhD, of Center for Vaccine Development and Global Health, University of Maryland School of Medicine, Baltimore, and colleagues explained in Annals of Internal Medicine.
As schools report high levels of remote absenteeism and worse mental health outcomes among students, many experts—including the American Academy of Pediatrics—have advocated for a return to in-person classrooms.
The question is, what degree of Covid-19 mitigation is enough to offset Covid-19 infection risk and reopen schools as safely as possible? To find their answer, Fitzpatrick and colleagues simulated SARS-CoV-2 transmission dynamics in both elementary and high school settings when mitigation efforts such as symptom-based isolation, asymptomatic screening, and alternative classroom schedules were implemented.
They found that while in-person learning increased transmission compared to remote learning, elementary schools could control Covid-19 transmission with only medium mitigation efforts—masking and distancing, with moderate uptake—while maintaining a traditional five-day schedule. On the other hand, “[i]n high schools, stronger mitigation or prevention strategies would be required to meet the control threshold,” and weekly asymptomatic screening would be required to safely hold to a five-day schedule, they wrote. In addition, Covid-19 vaccination among school staff further reduced transmission risk.
They also found that, while in-school mitigation efforts are certainly necessary, controlling community Covid-19 transmission is key to keeping the virus out of the classroom.
“Although determining the exact risk for these low-probability but high-consequence events is difficult, local transmission determines the number of cases that enter a school, and therefore such rare but consequential out-breaks become increasingly likely when local incidence is high,” they wrote—however, they added, “although schools may decide that in-school transmission risk is too high above certain levels of local incidence, our results do not suggest that K-12 education with mitigation or modified schedules is likely to be a primary driver of sustained community transmission.”
“If schools can reopen for in-person learning, then they must, to avert the mental health and educational crisis that is at our doorstep,” Ted Long, MD, MHS, of New York City Health + Hospitals in New York City, wrote in an editorial accompanying the study.
Long noted that the U.S. has seen a major increase in urgent mental health visits from 2019-2020, with the proportion of mental health-related ED visits increasing by 24% and 31% for children ages 5-11 and 12-17 years, respectively. And, he added, while there is substantial evidence that remote learning can adversely impact social development, there is also evidence suggesting that children learning from home have the same risk for SARS-CoV-2 infection as students attending in-person classes.
“One of the most powerful tools we have to support children’s and adolescents’ mental health is in-person learning,” he wrote. “There is no replacement for the opportunities it offers to foster social development and education.” Based on the findings from Fitzpatrick et al, Long concluded that it is imperative that the U.S. reopen schools “to ensure that young people emerge from this pandemic healthy.”
For their analysis, Fitzpatrick and colleagues created an agent-based network model to simulate Covid transmission in elementary and high-school communities, “including home, school, and interhousehold interactions.”
The models consisted of an average elementary school population (n=638 students) and an average high school population (n=1,451 students)—plus faculty, staff, and adult household members—and daily local community incidence varied from one to 100 cases per 100,000 persons. The study interventions included isolation of symptomatic individuals, quarantine of an infected individual’s contacts, reduced class sizes and alternative schooling schedules (five-day schedule, cohorting [a five day schedule with restricted out-of-classroom contact], half class sizes, hybrid [A/B] scheduling [classes subdivided into two cohorts, group A attends in person Monday/Wednesday and group B Tuesday and Thursday]), staff vaccination, and weekly asymptomatic screening for SARS-CoV-2. The study authors defined a reopening strategy as “controlling transmission” in a group if it “resulted on average in less than a 1-point increase in the percentage of the group that was infected, compared with remote learning.” They also categorized mitigation uptake into three categories:
- “Low uptake: Schools implemented no or minimal general infection control measures, such as masking and distancing.
- “Medium uptake: Schools implemented masking and distancing, and adherence was moderate, such that the risk for transmission given infectious contact was two-thirds that in a school with low uptake.
- “High uptake: Schools implemented masking and distancing, and adherence was high, such that the risk for transmission given infectious contact was one-third that in a school with low uptake.
Fitzpatrick and colleagues found that high schools required more stringent mitigation strategies than elementary schools. Elementary schools with low mitigation uptake and classroom quarantine under a five-day schedule were projected to have 1.7 secondary cases over 30 days after infection of a single index case patient, which decreased to 0.9 cases with medium mitigation and 0.3 cases with high mitigation. The greatest transmission reduction for elementary schools came from switching to an A/B schedule—0.1 to 0.4 cases, depending on uptake level.
High schools saw a greater potential for larger outbreaks following an index infection, the study authors noted; with low mitigation uptake and classroom quarantine under a five-day schedule, one index case led to 23 secondary cases over a 30-day period, but high uptake reduced this rate to 2.0 cases.
Classroom quarantine had a modest effect on transmission rates, though the effect did not differ greatly between low and high mitigation strategies. Likewise, teacher vaccination only conferred a small reduction to overall transmission rates—however, vaccination had a substantial impact on transmission to teachers. Weekly screening, meanwhile, “was projected to reduce secondary cases by a large degree compared with symptomatic isolation, classroom quarantine, or teacher vaccination, to an average of 0.3 to 0.8 cases with a 5-day schedule in elementary schools (varying by uptake of in-school prevention) and to 0.9 to 5.0 cases in high schools,” the study authors found. The effect was greatest when paired with low mitigation strategies: from 1.7 to 0.8 cases in elementary schools and from 23 to 5.0 in high schools.
Fitzpatrick and colleagues concluded that most in-school Covid transmission can be deterred through strategies that cut infection in the individual classroom, such as distancing, masking, or reducing class sizes. Switching to an A/B schedule can lead to fewer infections, and weekly screening for asymptomatic infection is particularly valuable for maintaining five-day schedules, they added.
Study limitations included uncertainty regarding the susceptibility and infectiousness of children and low precision regarding the effectiveness of specific countermeasures, particularly given the proliferation of new SARS-CoV-2 variants, particularly B.1.1.7.
Schools can safely reopen if Covid-19 mitigation strategies are maintained in classrooms, with a hybrid learning schedule and asymptomatic SARS-Cov-2 screening proving the most effective strategies for reducing infection rates.
This simulation study suggests high schools will require stronger mitigation strategies in order to control Covid-19 transmission compared to elementary schools.
John McKenna, Associate Editor, BreakingMED™
Fitzpatrick reported salary support paid to her institution from National Institutes of Health.
Long had no relevant relationships to disclose.
Cat ID: 190
Topic ID: 79,190,730,933,190,926,138,43,192,927,151,928,925,934