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Reopening Schools and the Dynamics of SARS-CoV-2 Infections in Israel: A Nationwide Study

Our take —

A national study in Israel found that SARS-CoV-2 test positivity and incidence increased across pediatric and adult age groups following school reopenings in May 2020; increases in SARS-CoV-2 hospitalizations and deaths, however, were not observed until later in the summer, coinciding with the lifting of other restrictions on large social gatherings. This study had major limitations, including the use of aggregate national data and short time intervals in analysis, restricted to just three weeks following school reopenings.

Study design

Ecological

Study population and setting

On May 3, 2020, schools in Israel were partially reopened following nearly two months of closure (since March 14). By May 17, schools throughout Israel were completely reopened through the end of the academic year (June 19 for secondary schools and June 30 for elementary schools). While Israel imposed standard public health mitigation measures within schools upon reopening (i.e., mask use, maintaining physical distance from others), they did not employ cohort-based mitigation measures (e.g., keeping the same students and teachers together in the same classroom) in contrast to other countries. Using age-disaggregated COVID-19 incidence, hospitalization, and mortality estimates, the authors investigated the impact of partial and complete school reopenings on SARS-CoV-2 transmission dynamics, comparing changes in SARS-CoV-2 test positivity, incidence (7-day average of new cases per 100,000 persons), hospitalizations, and deaths in school-aged children/adolescents (ages 19 and under) and the general adult population (ages 20 and above) in the week before and the two to three weeks following school reopenings.

Summary of Main Findings

In the 21-27 days following school reopenings, SARS-CoV-2 test positivity increased significantly across adult age groups but not among children <10 years (Rate Ratio [before vs. after reopening]: 1.46, 95% CI: 0.85–2.51) or 10-19 years (RR 0.93, 95% CI: 0.65–1.34). Accounting for the number of SARS-CoV-2 tests performed, COVID-19 incidence increased significantly in adults and children <10 years (Incidence Rate Ratio [IRR]: 2.2, 95% CI: 1.56–3.11) and 10-19 years (IRR 1.29, 95% CI: 0.94–1.76) in the two and three weeks following school reopenings. By July 31, children 19 years and younger accounted for nearly one-third (29%) of SARS-CoV-2 infections in Israel, but this increase in SARS-CoV-2 test positivity and incidence grew most dramatically in children and adolescents (<20 years) after schools closed permanently for the academic year (June 19 and 30 for secondary and elementary schools, respectively). COVID-19 hospitalizations and deaths remained relatively stable in the 49-day period following school reopenings, increasing significantly in the 21-28 days and 28-34 days, respectively, following easing of restrictions on attending large social gatherings (on June 12) (hospitalizations: IRR 3.95, 95% CI: 3.2–4.8; mortality: IRR 4.0, 95% CI: 1.9–8.3). SARS-CoV-2 test positivity and 7-day average COVID-19 incidence increased significantly across pediatric and adult age groups after June 12, when restrictions on attending large social gatherings were eased.

Study Strengths

This study adjusted for changes in testing rates over time, which may have reduced impacts of surveillance biases introduced by changing test guidelines over calendar time. Israeli surveillance protocols following school reopenings, including testing of asymptomatic household contacts of school-attending children infected with COVID-19, likely resulted in more accurate estimates of SARS-CoV-2 burdens among school-aged children, compared to symptomatic testing only. Lastly, the study’s use of multiple SARS-CoV-2 transmission metrics, from test positivity to mortality, provided a detailed picture of the COVID-19 epidemic in the context of school reopenings.

Limitations

This study had several key limitations. First, trends in COVID-19 test positivity, incidence, hospitalizations, and deaths were only compared between the seven days before school were reopened and the two to three weeks after schools were reopened; this narrow time interval prohibited assessment of potential downstream impacts (i.e., COVID-19 hospitalizations and deaths) that could occur following multiple generations of SARS-CoV-2 transmission. Moreover, it may take several weeks or longer before outbreaks or transmission in schools to occur; if such transmission events occurred, they would not have been captured in this study. Second, because school reopenings occurred within days of other restrictions on social gatherings being lifted, the independent effect of school reopenings on SARS-CoV-2 transmission cannot be disentangled from other policy changes. Third, because children infected with SARS-CoV-2 are more likely than adults to present asymptomatically, estimates of SARS-CoV-2 infections in pediatric age groups may be underestimated. Fourth, given the author’s exclusive use of national data, the estimates generated in their analyses do not account for background subnational differences in COVID-19 incidence, hospitalizations, or deaths. Fifth, the absence of any information on control measures implemented in schools during reopenings, or how these control measures may have differed across schools, makes the results difficult to interpret or to generalize to other settings. Lastly, because schools in Israel were reopened at a time when community SARS-CoV-2 transmission had declined substantially since March 2020, the generalizability of these results may be limited to settings with low COVID-19 burdens at the time of school reopenings.

Value added

This is among the first studies globally to estimate impacts of school reopenings on national age-specific SARS-CoV-2 transmission dynamics.

This review was posted on: 5 February 2021