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COVID-19: Mask mandates in school reduced community spread

  • A recent study investigated the association between the opening of K-12 schools and the community transmission of SARS-CoV-2 in the United States.
  • The study found that counties with in-person or hybrid schooling, especially those without a staff mask mandate, experienced a higher number of COVID-19 cases and deaths after reopening than those providing remote learning.
  • Fully opening K-12 schools with in-person learning was associated with a 5-percentage-point increase in the growth rate of COVID-19 cases.
  • There was a strong association between opening K-12 schools without mask mandates for school staff and case growth rate.
  • This study underscores the importance of mitigation measures, such as mask wearing, for in-person schooling until most eligible children and school staff are vaccinated.

The emergence of the Delta variant, the lack of vaccines authorized for children under 12 years of age, and vaccine hesitancy have meant that discussions about mitigation measures in schools, such as mask wearing, have continued.

Although children and adolescents are less likely than adults to develop severe illness after a SARS-CoV-2 infection, a small percentage of children may require hospitalizationTrusted Source due to complications associated with severe COVID-19.

Moreover, the virus can transmitTrusted Source from children with a SARS-CoV-2 infection, even when they develop mild symptoms or remain asymptomatic.

However, the results from previous studies evaluating the impact of school reopenings on the community transmission of SARS-CoV-2 have been mixed.

While some studiesTrusted Source show limited community transmission due to SARS-CoV-2 infections in school children, others suggestTrusted Source that school closures are associated with a decline in COVID-19 incidence and mortality in the community.

A recent study, which appears in the journal Proceedings of the National Academy of Sciences of the United States of America, takes a fresh look at the data. The study evaluated the effects that school openings and mitigation measures in schools had on COVID-19 cases and deaths in the community.

The study’s corresponding author, Dr. Hiroyuki Kasahara, a professor at the University of British Columbia, Canada, told Medical News Today:

“Our paper analyzes how an increase of COVID-19 cases is related to the timing of opening K-12 schools across different counties in the U.S. and finds that the in-person opening of K-12 schools is positively associated with an increase in the growth rate of cases. We find that the association of K-12 school visits with case growth is stronger when mask wearing is not mandated for staff at school.”

“This finding indicates that, without mitigation measures such as mask mandates in place at school, the transmission within schools would happen and may result in community transmission, which, in turn, would lead to a rise in cases and deaths. The finding has significant implications on the need for enforcing precautionary actions at school and for giving vaccine priority to education workers,” continued Dr. Kasahara.

Preliminary findings

To assess the impact of school reopenings on SARS-CoV-2 transmission, the researchers used county-level data on K-12 school reopenings between April and December in 2020.

The researchers obtained data revealing whether most students in the county attended schools involving in-person, remote, or hybrid teaching methods. They also acquired information on the masking requirements for school staff members in each county.

In addition, the researchers used de-identified data from mobile devices to track the mobility of community members in each county. Using this data, they were able to track changes in the frequency of visits to schools, workplaces, restaurants, places of worship, and recreational places that could be associated with the reopening of schools.

The researchers then investigated whether the reopening of schools was associated with an increase in COVID-19 cases and deaths in those counties.

Their preliminary analysis revealed that the reopening of schools resulted in a higher number of COVID-19 cases and deaths in counties with hybrid or in-person teaching than in those with remote learning. Moreover, the increase in COVID-19 cases and deaths was more pronounced in counties without mask mandates for staff members.

The de-identified mobile device data showed that the reopening of schools in counties with hybrid or in-person education was also associated with an increase in visits to schools and full-time workplaces. The increase in visits to full-time workplaces suggests that parents or caregivers returned to work upon the resumption of in-person schooling.

Limitations of the preliminary analysis

The study authors recognize that these preliminary findings have certain limitations.

For instance, a higher number of COVID-19 cases would entail the increased transmission of the SARS-CoV-2 virus and, as a result, more cases in the near future. Moreover, higher community transmission of SARS-CoV-2 could provoke changes in people’s behavior and the local implementation of mitigation measures.

These factors could skew the actual effect of school reopenings on COVID-19 cases and deaths.

The preliminary analysis of the impact of school reopenings on SARS-CoV-2 transmission did not account for these factors.

Consequently, the researchers analyzed the data using a statistical method called dynamic panel data modeling. This approach allowed them to control for variables that change over time, such as past infection levels and mitigation measures.

Controlling for variables     

After noting the actual numbers of cases in the preliminary analysis, the researchers carried out a subsequent analysis in which they investigated the association between school reopenings and the growth rate of, or percentage increase in, COVID-19 cases each week.

After controlling for the abovementioned variables, opening K-12 schools with in-person learning and the accompanying increase in visits to schools were associated with an increase in the growth rate of COVID-19 cases.

Specifically, fully reopening schools involving in-person learning was associated with a 5-percentage-point increase in the weekly growth rate of COVID-19 cases. In contrast, remote learning was associated with a lower COVID-19 case growth rate.

Furthermore, the association between in-person learning and the growth rate of COVID-19 cases was stronger in counties without a mask mandate for school staff.

Counties with mask mandates for school staff were also likely to have similar masking requirements for children, as well as the prohibition of sporting activities and more online learning.

These data thus support mitigation measures such as mask wearing and physical distancing to aid the resumption of in-person learning. Moreover, these results are consistent with a recent reportTrusted Source that the Centers for Disease Control and Prevention (CDC) conducted.

Dr. Monica Gandhi, who is a professor at the University of California, San Francisco and was not involved in the study, noted that these results were indeed consistent with other research about school openings.

She explained to MNT, “large population-based studies in WisconsinTrusted SourceNorth CarolinaUtahTrusted Source, and New York City have continually demonstrated secondary transmission rates of less than 1% in school classrooms — even prior to adult vaccination — but those were performed in the setting of teacher masking.”

“A month after California reopened its schools in the fall of 2021, despite the Delta surge, with mitigation strategies — including universal masking, regardless of vaccination status — and high rates of teacher/parent vaccination, San Francisco recorded zero in-school transmissions, and Los Angeles recorded two.”

“Masking in schools is an important mitigation strategy to allow for school openings,” Dr. Gandhi concluded.

Contribution of school visits

The preliminary analysis of de-identified mobile device data showed that increased SARS-CoV-2 transmission was associated with an increase in visits to both schools and workplaces.

Therefore, the increase in case numbers could be due either to children attending schools or to parents and caregivers returning to their workplaces. Further analysis of the data that the team gathered from the de-identified mobile devices suggested that school visits contributed to a large extent to the increase in cases.

Although an increase in the spread of SARS-CoV-2 may occur due to in-person learning, the authors caution that this must not solely inform policy decisions. They note that school closures can have a negative impact on children’s mental and physical well-being, as well as that of their parents or caregivers. Due to this, officials should make decisions only after weighing the costs and benefits of school closures.

Lastly, the authors note:

“[G]iven their relatively low implementation costs, our findings strongly support policies that enforce masking and other precautionary actions at school and prioritizing vaccines for education workers and elderly parents/ grandparents.”

Strengths and limitations

Dr. Kasahara outlined to MNT some of the study’s strengths, which included “the use of a comprehensive county-level dataset [that] includes the information not only on cases and deaths but also on school opening dates and learning modes — in-person, hybrid, and remote learning.”

Dr. Kasahara noted that the study had certain limitations. For instance, the collection of the data that the scientists analyzed took place before the Delta variant arrived on the scene.

“With the Delta variant, mitigation measures would be even more important for safe school openings — not only for stopping community transmission but also for stopping children from being hospitalized,” he explained. “With the Delta variant, more and more children are hospitalized in the U.S. and elsewhere after school opening.”

The authors also acknowledge that the team was not able to control for variables, such as changes in personal behavior over time, which could have influenced the analysis. They also note that the study was observational and did not show a causal effect of in-person schooling on SARS-CoV-2 transmission.

 

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