Seasonal epidemics of respiratory syncytial virus (RSV) have a significant global health burden in children worldwide.The virus is active year-round, with its transmission predominant in the winter months. Mitigation measures implemented during the COVID-19 pandemic had an unintended consequence of suppressing the RSV epidemic over the winter. This resulted in a dramatic decline in the number of cases of RSV observed during winter of 2020–2021 and an increase in the number of children without any natural immunity to the virus. As the mitigation measures used to control COVID-19 were relaxed in the latter half of the pandemic, there is an ongoing risk that RSV cases will increase sharply and unpredictably.
RSV is a common respiratory pathogen that causes infection of the lungs and respiratory tract. In adults and healthy older children, symptoms include a runny nose, coughing, sneezing and fever—similar to the common cold. However, the illness has a significant global burden as the second leading cause of death in children under the age of one. Similarly to COVID-19, RSV is spread through droplets from the nose and throat of infected people or contact with fomites (i.e., infected objects and surfaces). The COVID-19 pandemic and the non-pharmaceutical interventions implemented to ensure its control have had widespread implications for the epidemiology of many other communicable diseases, including RSV. According to GlobalData’s forecast, in the UK it was estimated that in 2022 there would be over 1,900,000 seropositive prevalent cases of RSV in children under the age of one. However, these cases will likely be an underestimate if the number of cases of RSV increases sharply and out of season.
A study by Bardsley and colleagues published in the Lancet Infectious Diseases in September 2022 modeled the impact of non-pharmaceutical interventions targeting COVID-19 on the epidemiology of RSV in England. Bardsley and colleagues found that at the start of the pandemic, cases of RSV fell sharply during the 2020–21 winter, followed by a substantial increase in transmission over the following summer. The study found that this was followed by a dramatic surge in RSV activity in 2021, including a 10.7% rise in hospital admissions and 11,225 extra lab-confirmed cases, equating to an increase of 1,258%. The move away from COVID-19 restrictions enabled the virus to return to more seasonal and typical transmission patterns, particularly in an immunologically naïve population.
Bardsley and colleagues found that during winter of 2020–21 in England, there were 10,280 fewer lab-confirmed cases – a 99.5% decrease compared to in previous winters before the pandemic. Moreover, RSV-associated hospital admissions dropped by 73.7% among children under the age of five. COVID-19 control measures such as lockdowns, closure of schools, and social distancing, which all limited close contact between young children, largely explain the decrease in RSV transmission during this period.
As many children had not been exposed over the previous winter, there were a greater number of people than usual without natural immunity to RSV and who were susceptible to infection, allowing for the unprecedented rates of RSV observed in the summer of 2021. As the pandemic continues, it is important to be aware of the changing epidemiological patterns of RSV and the additional pressure that this may place on healthcare services this winter.