Main text
Introduction
In temperate regions, respiratory syncytial virus (RSV) typically
circulates in the winter months, causing more severe illness
particularly in infants and older adults which often results in
hospitalisation, including admission to intensive care units1,2. There are often periods of co-circulation with
influenza and other seasonal respiratory viruses. RSV is monitored
through sentinel and/or non-sentinel surveillance in many countries,
territories and areas (henceforth referred to as countries) in the World
Health Organization (WHO) European Region, the European Union (EU) and
European Economic Area (EEA) countries (hereafter referred to as
Europe). These sentinel surveillance systems were originally established
for influenza and previously described 3. A number of
RSV vaccines are approaching possible licensure 4–6.
Monoclonal immunoglobulins are available as prophylaxis during the
typical period of RSV circulation to protect young infants with chronic
underlying heart and lung disease at higher risk of severe disease7.
The emergence and spread of Severe Acute Respiratory Syndrome
Coronavirus 2 (SARS-CoV-2) in early 2020 and the subsequent public
health and social measures (PHSM) implemented by Member states to reduce
its transmission and anticipated morbidity and mortality have disrupted
the spread of other respiratory viruses, including RSV, in both the
southern 5,8,9 and northern hemispheres10–12.
This work aims to describe the epidemiology of RSV in Europe during the
2020/21 and 2021/22 winter seasons (weeks 40/2020 to 20/2021 and 40/2021
to 20/2022) and two inter-seasonal periods (weeks 21 to 39/2021 and 21
to 39/2022) through three surveillance systems (primary care sentinel,
secondary care Severe Acute Respiratory Infection (SARI), and
non-sentinel surveillance) in comparison to historical pre-COVID-19
pandemic data.
Methods
This retrospective epidemiological analysis of RSV used weekly data
submitted to The European Surveillance System (TESSy) by the European
Regional surveillance network jointly coordinated by ECDC and the WHO
Regional Office for Europe. As RSV is not notifiable, reporting is
voluntary. Weekly counts of detections and specimens tested in 48
reporting countries between week 40/2020 and week 39/2022 were
downloaded on 14th October 2022. Countries were
included in this analysis if at least one sample tested was reported.
Using specimens taken from selected cases of influenza-like illness
(ILI) and acute respiratory infection (ARI) presenting toe primary care
sentinel surveillance system (these systems have been described
previously 3, we calculated the aggregated weekly
counts of RSV detections and tests and the percentage positivity when at
least ten tests were performed. These counts and percentages were
compared to the four previous seasons (2016/17 to 2019/20; hereafter
referred to as pre-COVID-19 pandemic seasons). Using weekly RSV
percentage positivity from four pre-COVID-19 pandemic seasons of
sentinel data, we used the Moving Epidemic Method (MEM) to calculate
RSV-specific epidemic thresholds for each country (Supplementary table
2) and identify potential changes in seasonal patterns, as previously
shown 13. It is important to note that these
thresholds may differ from those used in country for surveillance
purposes. Epidemic activity was determined to have started when
percentage positivity was above the country-specific epidemic threshold
for the first of at least two consecutive weeks. The duration of the
epidemic period was defined as the total number of weeks above the
threshold (including non-consecutive weeks).
Similarly, aggregated weekly counts of detections and specimens tested
were calculated, along with percentage positivity, for SARI sentinel
surveillance (hospital inpatients meeting the case definition). Only two
countries reported data in 2020/21 and sixteen in 2021/22al periods;
historical data regarding number of tests performed were unavailable for
this surveillance system. Data included aggregated SARI cases by age
group (≤4 years, 5 to 14 years, 15 to 64 years and ≥65 years).
For the non-sentinel surveillance system, only the weekly counts of
detections were aggregated but percentage positivity could not always be
calculated given the unavailability and/or uncertainty around some of
the denominators. Specimens from this system were taken from patients
that originated from hospitals, schools, primary care facilities not
involved in sentinel surveillance, or nursing homes and other
institutions.
For all three systems, data in the study period were compared to
historical data. Some countries stopped surveillance or reporting data
to TESSy over the summer months for some surveillance systems
considered. All analyses were conducted in R version 4.0.514.
Results