Within-household SARS-CoV-2 transmission and vaccine effectiveness in the first three COVID-19 school outbreaks in northern Viet Nam, September–December 2021
Authors:   National Centre for Epidemiology and Population Health, College of Health and Medicine, Australian National University, Canberra, Australian Capital Territory, Australia, Vu Trang Thu ,   Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Ngo Tu Huy ,   Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam; Field Epidemiology Training Program, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Nguyen Khanh Cong ,   Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam; Field Epidemiology Training Program, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Lan Vu Thi ,   Ha Nam Center for Disease Control, Ha Nam, Viet Nam, Hanh Cu Thi Bich ,   Phu Tho Center for Disease Control, Phu Tho, Viet Nam, Son Le Hong ,   Thanh Hoa Center for Disease Control, Thanh Hoa, Viet Nam, Nguyen Huyen Thi ,   National Centre for Epidemiology and Population Health, College of Health and Medicine, Australian National University, Canberra, Australian Capital Territory, Australia; Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Nguyen Hien Thi ,   National Centre for Epidemiology and Population Health, College of Health and Medicine, Australian National University, Canberra, Australian Capital Territory, Australia; Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Ngu Nghia Duy ,   Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Tran Duong Nhu ,   National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Dang Duc-Anh ,   National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam, Vogt Florian ,   National Centre for Epidemiology and Population Health, College of Health and Medicine, Australian National University, Canberra, Australian Capital Territory, Australia; The Kirby Institute, University of New South Wales, Sydney, New South Wales, Australia, Pham Thai Quang ,   Department of Communicable Disease Control and Prevention, National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam; Department of Research Methodology and Biostatistics, School of Preventive Medicine and Public Health, Hanoi Medical University, Hanoi, Viet Nam
Published: October 2024

Objective: The risk of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from schoolchildren to their household and the protective effects of vaccination in these settings remain poorly understood. We assessed the transmission dynamics of schoolchildren with SARS-CoV-2 within their households and the protective effects of coronavirus disease (COVID-19) vaccination among household members in Viet Nam. Methods: We estimated the attack rate, vaccine effectiveness and adjusted risk ratio (aRR) of factors associated with SARS-CoV-2 transmission to household contacts of children confirmed to have COVID-19 who attended three schools in Ha Nam, Phu Tho and Thanh Hoa provinces between September and December 2021 using multivariable regression with household-level random effects. Results: This retrospective cohort study included 157 children infected with SARS-CoV-2 and their 540 household contacts. The attack rate among household contacts was 24.6% (133/540). Overall, vaccine effectiveness among household contacts was 39% (95% confidence interval [CI]: -1 to -63), higher among males than females and higher in adults aged >40 years. COVID-19 transmission was greater among female household contacts compared with males (aRR: 1.35, 95% CI: 0.94 to 1.95), although not statistically significant, and highest among those aged 19–39 years (aRR: 2.51, 95% CI: 1.50 to 4.21). Fully vaccinated household contacts had significantly lower infection risk (aRR: 0.46, 95% CI: 0.26 to 0.84). Discussion: We found substantial onward transmission of SARS-CoV-2 from schoolchildren to household members, and older people were more likely to be protected by vaccination. We recommend that schoolchildren and all household members living with schoolchildren receive at least two doses of a COVID-19 vaccine. Recognizing the role of schoolchildren in the onward transmission of COVID-19 is an important lesson learned by Viet Nam that can help not only in managing other outbreaks but also in protecting schoolchildren by predicting the progress of the outbreak and preparing for a timely response.