Study: Relaxation of Public Health Interventions for COVID-19 Has Strongest Impact on Children Aged 1 to 4 Years

Researchers suggest that winter 2020 to 2021 public health interventions lowered natural immunity in children and put them at greater risk of respiratory infection after restrictions were lifted.

National public health interventions mitigated the spread of the respiratory syncytial virus (RSV) COVID-19 in England during the 2020 to 2021 winter season. However, relaxation of these measures during summer 2021 created an unprecedented summer epidemic, according to the authors of a study published in The Lancet.

During winter 2020 to 2021 in England, there were 10,280 fewer COVID-19 cases counted in the labs; among children, laboratory-confirmed RSV cases decreased by 99% during this period. However, laboratory-confirmed cases of RSV increased by 1000% in summer of 2021.

“The absence of RSV activity in England during the winter of 2020–21 and then atypical activity in summer 2021… was most likely due to the introduction and subsequent relaxation of public health non-pharmaceutical interventions to mitigate the spread of COVID-19,” studyauthors wrote.

The effects of the national public health interventions on RSV were especially seen in young children. Typically, RSV causes bronchitis and bronchiolitis in young children. RSV is usually mild but remains the number 2 cause of death in infants. In England (study location) RSV cases among children peak in December.

The study’s objective was to evaluate transmission of respiratory infection within communities using non-pharmaceutical interventions. The findings showed that there was never a peak in RSV cases during winter of 2020 to 2021. However, the researchers reported 12,150 RSV cases during the summer of 2021, which appears to be 11,255 more cases than were predicted for the season.

The researchers also warned that the relaxation of national public health interventions may lower the immunity of children aged 5 and younger, leaving them more susceptible to RSV infection. During the summer of 2021, laboratory-confirmed RSV cases among children aged 1 to 4 years were especially prevalent, since children were “RSV-naïve” following lockdown.

“Although the result of smaller winter epidemics might appear beneficial, there is growing evidence of the potential of medium-term negative effects through immunity debt, in which a greater proportion of the population is susceptible to a disease after a long period of reduced exposure,” study authors wrote in the report.

The study had limitations. The first was applying a binary threshold for the COVID-19 intervention period. Additionally, RSV-associated disease may be overestimated, and the study population did not include people with RSV who do not use health services. Finally, there were methodological limitations, such as not including every confounding variable.

Models from the United States show that long-term non-pharmaceutical interventions can cause large-scale respiratory viral infections in the future. Data suggest that monitoring non-COVID-19 RSV indicators can inform future planning for health care systems and disease prevention.

“These systems will be invaluable for informing seasonal RSV planning in the context of ongoing COVID-19 transmission, as the magnitude and timing of future RSV epidemics remains to be seen,” study authors wrote in the report.


Bardsley M, Morbey R, Hughes H, et al. Epidemiology of respiratory syncytial virus in children younger than 5 years in England during the COVID-19 pandemic, measured by laboratory, clinical, and syndromic surveillance: a retrospective observational study. The Lancet. 2022. doi:10.1016/S1473-3099(22)00525-4