Understanding SARS-CoV-2 Delta and Omicron variant transmission and vaccine impact in schools and child-care settings in Australia: a population-based study

Abstract

Background: Over 214 million students globally have been affected by school closures during the COVID-19 pandemic. To address knowledge gaps on transmission of SARS-CoV-2 delta (B.1.617.2) and omicron (B.1.1.529) variants in educational settings we examined virus transmission in schools and early childhood education and care settings (ECECs) in New South Wales (NSW), Australia in relation to mitigation measures, including COVID-19 vaccination.

Methods: Secondary transmission from children and adults with laboratory-confirmed SARS-CoV-2 infection who attended a school (n = 3170) or ECECs (n = 5800) while infectious was investigated over two periods: 1) June 16 to September 18, 2021 (delta outbreak), and; 2) October 18 to December 18, 2021 (delta and omicron; schools only). Close contacts of cases underwent 14 days quarantine and SARS-CoV-2 nucleic acid testing. Secondary attack rates (SARs) were calculated and compared with state-wide notification data, school attendance, and vaccination status.

Findings: 1187 schools and 300 ECECs had students (n = 1349) or staff (n = 440) attend while infectious. Of 24,277 contacts investigated, most (91.8%; 22,297/24,277) were tested and 912 secondary cases identified. The secondary attack rate (SAR) was 5.9% in 139 ECECs and 3.5% in 312 schools. The risk of becoming a secondary case was higher in unvaccinated school staff (OR 4.7; 95% CI: 1.7-13.3), particularly ECEC staff (OR 9.0; 95% CI: 3.6-22.7) and unvaccinated school students than in vaccinated school staff. SARs were similar for delta (4.9%) and omicron BA.1 (4.1%) in the unvaccinated and higher compared with vaccinated contacts (0.9% and 3.4%, respectively). Increasing school attendance rates raised case incursions and secondary case numbers, but not community-wide infection rates.

Interpretation: Vaccination reduced SARS-CoV-2 transmission rates in schools, although less so for omicron than delta variants. Despite higher community-based transmission rates, in-school transmission remained low and stable with high attendance, suggesting that community restrictions, rather than school closures, best mitigated COVID-19 impacts.

Funding: NSW Government Department of Health.

Keywords: COVID-19; Education; Preschool; SARS-CoV-2; Schools; Transmission.

Fig. 1

New South Wales (NSW) population wide COVID-19 notifications between June 16, 2021 (first notified Delta case) and December 18, 2021 (last day of the school year), with: Panel A) daily number of schools and ECECs case incursion episodes, and; Panel B) daily school attendance rate and cumulative vaccination coverage (dose 1 and 2) in ages 12 years and older. ^#for information on COVID-19 School operations level see Supplementary Table S4.

Fig. 2

Adjusted odds ratios of a contact becoming a secondary case following SARS-CoV-2 exposure from a primary case in educational settings, by contact type (staff/student), vaccination status and setting type. ∗Adjusted for covariants: SARS-CoV-2 variant (delta (ref)/omicron/suspected omicron/unknown, primary case type (staff/student (ref)/both), primary case vaccination status (2-dose vaccinated (ref)/unvaccinated/1-dose vaccinated/mixed); There were no cases among 138 vaccinated primary school students. ECEC: Early childhood education and care; HS: high school; PS: Primary school; Students and staff from School for Special purposes (SSP) and K-12 schools were excluded from analysis.