Transmission and control of influenza and COVID-19 in school setting

Abstract

Children are recognized as important drivers of influenza transmission. Because children spend prolonged durations every day in schools – a semi-enclosed setting which provide opportunities for high intensity contact among children, it is likely that schools play an important role for the spread of influenza. On the other hand, while the understanding on the importance of schools for COVID-19 is still developing, schools have been considerably impacted during the pandemic.

This thesis aims to understand the transmission of influenza and COVID-19 within school settings, and to improve existing control strategies. I undertook a series of studies to better understand the transmission potential, transmission dynamics and transmission modes of influenza virus and SARS-CoV-2 in school settings, as well as control and mitigation measures with a focus on case-targeted measures, school closure/class dismissal, and school-based measures.

First, I conducted a longitudinal study and detected low prevalence of influenza virus RNA on touch-surfaces in kindergarten and primary schools. No viable influenza virus was recovered. My findings reaffirm the potential of indirect contact transmission, but suggests that indirect contact transmission is unlikely to have contributed significantly to the total transmission in schools.

Second, I designed and piloted a prospective cohort study with the primary objective of assessing the attack rate and asymptomatic fraction of seasonal influenza virus infections in kindergarten and primary schools. The pilot phase demonstrated feasibility of the study design, in particular weekly school visits during seasonal influenza epidemics to collect nasal swab samples from young children for active surveillance for infection.

Third, I conducted serial cross-sectional surveys during the COVID-19 pandemic to assess social activities and person-to-person contacts of school-aged children during class dismissal. The number of social contacts remained low during class dismissal periods, and out-of-home activities and non-household contacts reduced significantly as compared to resumption periods. There was no significant difference in infections among school-aged children and school workers comparing the two periods. I also assessed secondary impacts of class dismissals including impact on household income and learning.

Fourth, I conducted a cross-sectional survey to investigate the extent of implementation and feasibility of school-based measures to reduce transmission. The minimal transmission of ancestral strain of SARS-CoV-2 in schools indicates the probable impact of school-based measures. Schools in Hong Kong adopted a wide range of administrative, engineering controls and personal protective equipment during the COVID-19 pandemic. Differences observed in the implementation and feasibility inform prioritization of the many possible measures for further investigation, shed light on strategies to better utilize school-based measures, and identify school types which possibly need more support to implement school-based measures.

Finally, as part of a project commissioned by the World Health Organization, I reviewed the evidence base on the effectiveness of case-targeted measures – isolation, contact tracing, and quarantine – in reducing influenza transmission. Overall, the systematic reviews suggested that case-targeted measures could be effective interventions, although the evidence identified was of relatively low quality of evidence. Controlled trials or natural experiments in community settings are needed to provide more robust evidence for the effectiveness of case-targeted measures.