Primary care sentinel surveillance
When compared to pre-COVID-19 pandemic seasons, there was an increase in the number of specimens tested for RSV in both the 2020/21 and the 2021/22 season: 21,803 and 36,040, respectively, compared to an annual average of 15,796 in pre-COVID-19 pandemic seasons (from 21 countries on average), representing a 38% and 128% increase, respectively. More countries reported during the 2021/22 season than during the 2020/21 and pre-COVID-19 pandemic seasons (Figure 1A, B, Table 1).
A total of 19 countries reported only 195 RSV detections from a total of 21,803 primary care sentinel surveillance specimens tested during the 2020/21 seasonal period. This represents an overall positivity of 1%, ranging up to 7% in France, which was lower than in the four pre-COVID-19 pandemic seasons (mean of 1,669 positive specimens, 11% positivity from an average of 21 countries) (Figure 1A, B, Table 1). Only seven countries reported at least five detections during the 2020/21 season (Supplementary table 1). Only France and Switzerland saw clear waves of activity. Between weeks 5/2020 and 19/2021 in France, percentage positivity was above 10% for all but two weeks, whereas Switzerland saw percentage positivity between 4% and 17% between weeks 16 and 20/2021 (Supplementary table 1).
During the 2020/21 season, of the nine countries where the epidemic thresholds could be calculated, only France reported peaks of RSV positivity above its threshold. France, Germany and Slovenia experienced early starts to their 2021/22 seasonal period compared to the average starting week of pre-COVID-19 pandemic seasons (Figure 2).
During the 2021 inter-seasonal period, a total of 316 positive specimens from 5,076 specimens tested (6% positivity) were reported from 17 countries (Figure 1A, B and Table 1). A total of nine countries (Estonia (n=8, 5% positivity), France (n=5, 4%), Georgia (n=21, 3%), Germany (n=175, 7%), Ireland (n=7, 2%), the Netherlands (n=39, 22%), Slovenia (n=16, 16%), Switzerland (n=35, 9%) and Ukraine (n=5, 4%)) saw higher than usual activity (Supplementary Figure 1). Of the countries with inter-seasonal activity, three (Germany, the Netherlands and Slovenia) exceeded their MEM epidemic threshold, with only the Netherlands having experienced activity during this inter-seasonal time period in pre-COVID-19 pandemic seasons. This represents only sporadic detections, as numbers of collected samples are generally low in the inter-seasonal time period (Figure 2, Supplementary Figure 1).
During the 2021/22 season, 34 countries reported 2,018detections from 36,040 tests performed (6% positivity). This was higher than during the 2020/21 season, but lower than during the pre-COVID-19 pandemic seasons (Figure 1A, B, Table 1). A peak of 17% positivity was observed in week 40/2021 which then fell to 3% (week 2/2022) and remained below this level until the end of the season. Regionally, this peak was higher than in the pre-COVID-19 pandemic season when regional positivity did not rise above 5% for any given week (Figure 1B, Table 1). In six countries (Denmark, Slovenia, Sweden, United Kingdom (Northern Ireland, Scotland and Wales)), the start of the 2021/22 season was already discernible in the latter part of the 2021 inter-seasonal period with detections peaking before or after week 40/2021. Where possible to compare with pre-COVID-19 pandemic seasons (n=23 countries), 14 countries experienced similar or higher positivity. Positive specimens continued to be detected in several countries during the second half of the season leading into the 2022 inter-seasonal period, most notably in Georgia, the Netherlands, Spain and Switzerland (Supplementary Figure 1B).
During the 2022 inter-seasonal period, 375 detections were reported from 19,197 samples tested (2% positivity) from 27 countries. Both the number of tests performed and positivity for this period were higher than seen in pre-COVID-19 pandemic inter-seasons: up to 1,336 tests and up to 1% positivity (Table 1). Eight countries reported RSV activity outside of the characteristic winter season with at least five detections: Denmark (n=59, 3% positivity), Georgia (n=33, 5%), Germany (n=15, 1%), the Netherlands (n=40, 6%), Spain (n=103, 1%), Switzerland (n=9, 1%), United Kingdom (Scotland) (n=86, 9%) and Slovenia (n=12, 15%) (Supplementary Figure 1, Supplementary table 1). During this period, only the Netherlands and United Kingdom (Scotland) experienced RSV positivity reaching the epidemic levels previously calculated (Figure 2).