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Identifying the impact of non-pharmaceutical interventions on RSV transmission in a single-centre observational study
  1. Tara Anne Betts,
  2. Alice Elizabeth Darby,
  3. Faris Hussain,
  4. Martin Edwards
  1. Acute Child Health, Children's Hospital for Wales, Cardiff, UK
  1. Correspondence to Dr Martin Edwards; martin.edwards4{at}


During the COVID-19 pandemic, the introduction of non-pharmaceutical interventions (NPIs) resulted in an unprecedented reduction in the transmission of the respiratory syncytial virus (RSV), the predominant cause of bronchiolitis. As NPIs were eased, it was speculated that RSV transmission would return with an increase in the severity of bronchiolitis. In a large tertiary hospital, a dramatic reduction in the incidence of bronchiolitis was seen during the COVID-19 pandemic. The easing of NPIs correlated with an increase in RSV transmission particularly in the community; however, there was no evidence of an increase in the severity of bronchiolitis.

  • Virology
  • Epidemiology

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Before the COVID-19 pandemic, the incidence of bronchiolitis followed a typical annual season with the peak during the winter months of October to March. The introduction of non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic indirectly resulted in an unprecedented decrease in the transmission of the respiratory syncytial virus (RSV) and the incidence of bronchiolitis.1 It was speculated that as NPIs were eased, RSV would return with an increased severity of bronchiolitis.2

We retrospectively reviewed data from children admitted to the Children’s Hospital of Wales (CHfW) between 1 October and 31 March from 2015 to 2021. The incidence of admissions and severity before and during the COVID-19 pandemic were compared with the post-COVID-19 pandemic period between 1 April 2021 and 31 March 2022 as NPIs were eased in Wales. The study included children admitted to the hospital who were coded with respiratory conditions under the International Classification of Diseases Tenth Revision codes (J10-J18, J20-22, J45 and J46). The International Classification of Diseases codes cover all respiratory conditions in children to ensure no children with bronchiolitis were missed. The clinical details of every patient episode were reviewed to confirm the diagnosis of bronchiolitis prior to inclusion in the study data. The exclusion criteria included children over the age of 1 year, with extreme prematurity (under 32 weeks gestation), congenital heart disease, lung disease or neurological disability, and incomplete discharge advice letters.

Before the pandemic (2015 to 2020), an average of 240 (266 per 100 000 under 16 year olds) children were admitted with bronchiolitis to CHfW with an average of 149 swabs positive for RSV during the typical annual bronchiolitis season from October to March. RSV testing was performed on oropharyngeal swabs using PCR tests. This was a standardised test over the years of the study in the local hospital laboratory. During the pandemic, this was reduced to 15 (17 per 100 000 under 16 year olds) children admitted to CHfW between October 2020 and March 2021, with no swabs positive for RSV. After the pandemic, the incidence increased, with 148 (164 per 100 000 under 16 year olds) children admitted to CHfW from October 2021 to March 2022; of these, 79 swabs were positive for RSV.

Notably, the peak incidence of children admitted to CHfW with bronchiolitis after the pandemic occurred in August 2021 which correlated with the relaxation of NPIs in Wales on 7 August 2021. In August 2021, 44 (49 per 100 000 under 16 year olds) children were admitted to CHfW; of these, 31 swabs were positive for RSV. This supports the finding in other studies showing a shift in the bronchiolitis season after the pandemic.3 Figure 1 demonstrates the distribution of the 252 (279 per 100 000 under 16 year olds) children admitted to CHfW from April 2021 to March 2022. Our data aligns with data collected from Public Health Wales which correlated with cases presenting to the CHfW, where the highest incidence of RSV was between August and October 2021 as seen in figure 2.4

Figure 1

Monthly incidence of RSV and other viruses detected on throat swab or nasopharyngeal aspirate from 1 April 2021 to 31 March 2022 from patients admitted to CHfW. The respiratory viruses tested in 2021/22 included coronavirus SARS-CoV-2, influenza A, influenza B, RSV, adenovirus, parainfluenza, rhinovirus, enterovirus, seasonal CoV, HMPV and mycoplasma. RSV, respiratory syncytial virus; CHfW, Children’s Hospital of Wales; HMPV, human metapneumovirus.

Figure 2

Graph from Public Health Wales NHS Trust, demonstrating RSV incidence rate in those under the age of 5 years in Wales from 2019 to 2023.4 RSV, respiratory syncytial virus.

To assess the severity of bronchiolitis before, during and after the COVID-19 pandemic, we compared the number of patients admitted to the ward, length of hospital admission, requirement for nasogastric feeding or high flow oxygen, and children being escalated to paediatric intensive care unit or high-dependency unit (table 1). Despite Public Health Wales (PHW) reporting a very high intensity of RSV within the community, this did not translate to increased incidence and severity of bronchiolitis in CHfW.4

Table 1

Table demonstrating the total number of patients presenting to and those admitted to the Children’s Hospital for Wales, the length of admission, those requiring nasogastric feeding support and those requiring high flow nasal oxygen support and the total number of those children being escalated to PICU/HDU from October to March in the 5 years prior to the COVID-19 pandemic (2015–20), during the pandemic (2020–21) and post-pandemic (2021–22)

Several factors may explain the lack of increase in severity. First, increased testing of patients with respiratory symptoms may have contributed to the higher detection rates of RSV in the community. Second, parental hesitancy regarding hospital attendance during the COVID-19 pandemic may have continued despite restrictions easing.5

Our study has several limitations which include that it is a single-centre study and only children admitted to hospital were included in the data. Data regarding severity were taken from discharge summaries created by clinicians at the time of patient discharge; therefore, our study data relied on the clinicians including interventions such as nasogastric tube insertion, oxygen use and intravenous fluids.

It remains to be seen if the typical annual seasonality of bronchiolitis will return to the pre-pandemic winter months. Data from PHW reflect a return to the regular RSV season in the winter months of 2022–23; however, RSV incidence rates remain very high.4 Currently, in discussion is the use of maternal RSV vaccine which aims to reduce the global burden of RSV-associated illness and this may further affect future trajectory of RSV bronchiolitis.6 Future data will demonstrate the full impact on hospital admissions and severity of changes in the RSV season and the need for a vaccination programme.

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  • Contributors MOE was involved in the planning and design and supervised the data collection and helped to draft and edit the manuscript. MOE is responsible for the overall content as guarantor. TB and AD contributed equally to this paper; they wrote the draft manuscript, collected and analysed the data. FH supervised the draft manuscript and collected data.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.