Non-sentinel surveillance
A total of 18 countries reported at least one non-sentinel RSV detection in the 2020/21 season, with a total of 6,966 detections. This compares to an average of 49,738 detections from 32 countries in pre-COVID-19 pandemic seasons (Figure 1C, Table 1). Between weeks 40/2020 and 1/2021, fewer than 60 weekly detections were recorded, much less than the weekly average during the pre-COVID-19 pandemic seasons for the same weeks: 180 (week 40) to 3,437 (week 1). Detections peaked in week 12/2021 (Iceland and Ukraine) with 722 RSV detections and fell thereafter until week 18/2021. Between weeks 12 and 18/2021, the number of detections was comparable to pre-COVID-19 pandemic seasons (Figure 1C). For the countries with at least one historical season for comparison (n=17), only Iceland and Ukraine experienced more detections (Supplementary table 2) and Finland, Greece, Hungary, Poland, Portugal, Republic of Moldova, Serbia, and the United Kingdom saw an earlier peak in 2020/21 than in pre-COVID-19 pandemic seasons.
The 2021 inter-season saw 18,325 RSV detections reported from 20 countries, all of which could be compared to pre-COVID-19 pandemic seasons and mostly had higher numbers in 2021 in comparable weeks (average of 220 detections from 13 countries), with the exceptions of Estonia and Latvia (Figure 1C, Table 1, Supplementary table 2). This period was characterised by a gradual rise in detections (peaking in week 39/2021 with 2,646 detections) which had previously not been reported.
During the 2021/22 season, 62,426 detections were reported from 34 countries, of which 32 could be compared to pre-COVID-19 pandemic seasons (Figure 1, Table 1). The start of the 2021/22 season was a continuation of the high levels of detections already seen during the 2021 inter-seasonal period, with two peaks of detections: weeks 40/2021 (observed in Denmark, Slovenia, United Kingdom (Northern Ireland, Scotland, Wales) and 46/2021 (observed in France and Spain). From week 48/2021 until week 7/2022, the numbers of positive detections then gradually fell to levels lower than in pre-COVID-19 pandemic seasons. Between weeks 17 and 20/2022, the weekly average of detections was 514, higher than any pre-COVID-19 pandemic season (Figure 1C). Of the countries with historical comparisons, nine recorded fewer, 10 recorded more and 13 recorded a similar number of detections than in pre-COVID-19 pandemic seasons (Supplementary table 2).
Most countries recorded unusually high and/or early peaks of activity during the 2021/22 season. Some countries (Iceland, the Netherlands) saw a biphasic seasonal activity. Others, (Denmark, Portugal, Russian Federation, Slovenia, United Kingdom (England, Scotland and Wales)) saw their number of detections decline after an early peak but then rise into the 2022 inter-seasonal period Supplementary table 2).
The 2022 inter-season saw 8,876 RSV detections from 24 countries, of which 18 had historical data for comparison (Figure 1C, Table 1, Supplementary table 2). Bulgaria, Iceland, Portugal, Russian Federation and United Kingdom (Northern Ireland and Scotland) observed more detections than during pre-COVID-19 pandemic inter-seasons but without a distinct peak of activity (Supplementary figure 2). In contrast, the Netherlands and United Kingdom (Wales) did experience a peak of detections in weeks 23/2022 and 28/2022, respectively. Denmark, France, Slovenia and Spain reported a rise in activity late in the period and leading into the 2022/23 season (Supplementary figure 2).