SARS-CoV-2 Delta and Omicron transmission within educational settings in relation to community-based outbreaks and mitigation measures

In a recent study posted to the Preprints with The Lancet* server, researchers assessed whether school closures during coronavirus disease 2019 (COVID-19) outbreaks prevented viral transmission in Australia. In particular, they focused on schools and early childhood education and care settings (ECECs) in New South Wales (NSW).

The researchers addressed knowledge gaps in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission dynamics for periods corresponding to two COVID-19 outbreaks caused by SARS-CoV-2 variants of concern (VOCs), Delta and Omicron.

Background

The school closures during the unprecedented COVID-19 pandemic adversely impacted the lives of millions of children globally. This impact was worse for younger children, especially those struggling academically and those belonging to lower socioeconomic groups. Studies also documented the immense impact on many children's mental health due to prolonged social isolation.

Most children have mild or asymptomatic COVID-19; hence, they do not appear to be the drivers of SARS-CoV-2 transmission at the community level. Yet, there is a shortage of studies that have attempted to present empirical evidence supporting the non-closure of educational institutions.

About the study

In the current prospective observational cohort study, researchers assessed SARS-CoV-2 transmission in education settings, from infected cases to contacts, during Delta and Omicron VOCs circulation in Australia. They stratified their findings by setting the types and vaccination status of the participating students and staff members. Additionally, they compared their results with COVID-19 incidence rates at the community level and reported severe disease outcomes.

In this study, 1,349 and 440 students and staff members from 1,187 schools and 300 ECEC attended their institution while being infectious. The team assessed the secondary attack rate (SAR) from these children and adults with confirmed SARS-CoV-2 infection between June 16-September 18, 2021, and October 18-December 18, 2021. They compared the so computed SAR data with state-level data, their attendance, and vaccination status. Furthermore, they investigated their 24,279 contacts and performed COVID-19 diagnostic testing on 93.2% of them to identify secondary cases.

Study findings

The observed SAR for 312 schools and 139 ECECs was 3.5% and 5.6%, respectively. The overall SAR during both study periods was four-fold higher than for the ancestral strain predominance era (4% vs. 1.2%). Unvaccinated staff was at a higher risk of becoming a secondary case. It is also noteworthy that SARs were comparable for Delta and Omicron periods (4.6% and 5%) in the unvaccinated participants but higher relative to vaccinated close contacts, which were 1.3%, and 2.2%, respectively.

The researchers noted an increase in the frequency of school incursions following Omicron's emergence in late 2022. Likewise, increasing school attendance rates surged case incursions and secondary cases. It had no impact on community-level transmission, although the Australian government had relaxed public health measures restricting community-level mixing around the same time. Notably, at almost the same time, by 30 October 2021, 60% of 12 to 15-year-olds in NSW had received their primary vaccination series.

Considering such high vaccination rates, even with Omicron's advent, case-to-contact transmission rates in highly vaccinated 12-year-olds did not increase much compared with Delta VOC transmission. The authors could, thus, compare the COVID-19 risk in schoolgoers by vaccination status and exposed close contact with SARS-CoV-2 VOC type.

Since the Omicron VOC had a higher potential to escape vaccine-induced immunity, the rate of Omicron infections in children and school staff after coming in close contact with a case was higher though comparable between vaccinated and unvaccinated individuals. Yet, vaccination, especially booster shots, protected infected children and staff against severe disease.

Consequently, despite multiple outbreaks in NSW post-Omicron emergence, and frequent testing enabling outbreak detection, it did not result in prolonged school closures. Overall, SAR in schools and ECECs remained much lower than in households and social gatherings, even after Omicron's emergence.

The researchers also noted that staff presented with more primary and secondary COVID-19 cases than children. However, it is most likely because they work closely with students and other staff, especially in special purpose schools. Fortunately, hospitalization rates during Delta and Omicron transmission periods among SARS-CoV-2-infected children and staff remained low. Most hospitalizations occurred in unvaccinated staff members (56.2%), not children. Most children had mild disease, and even unvaccinated infected younger children did not appear to be at higher risk of severe COVID-19.

Conclusions

The current study results favor keeping schools open and continuing teaching offline because school closures had no association with high rates of community SARS-CoV-2 transmission in NSW. More importantly, this data could inform future vaccination policies in Australia.

Furthermore, the results highlighted the significance of prioritizing COVID-19 vaccination for school staff and reaffirmed that children, even when attending schools, are not drivers of community-level SARS-CoV-2 transmission. There is also an urgent need for more robust monitoring systems and evidence-based decision-making for continuous and safe delivery of offline teaching during the ongoing COVID-19 pandemic.

*Important notice

Preprints with The Lancet publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.