Respiratory syncytial virus (RSV) is the leading cause of acute bronchiolitis, the most common childhood respiratory infection and the leading reason for admissions in children under one year old. Between November and March, Catalonia experienced an annual RSV epidemic, with an epidemic peak in late December, before the first influenza cases were detected. This pattern was constant until the arrival of the SARS-CoV-2 coronavirus in March 2020. Back then, one of the first measures was to close schools. Based on the data we had on the flu, it was thought that the child population might be the most contagious for Covid-19. It turned out that, contrary to expectations, adults were mainly responsible for the transmission of SARS-CoV-2. After the first wave of the pandemic, boys and girls began contracting SARS-CoV-2, although they did so mildly and about half had no symptoms.
The arrival of the first fall-winter (2020-2021) pandemic created great uncertainty about what would happen to the flu and RSV. The prevalence of these viruses was surprisingly declining compared to other years until they emerged out of their usual season in spring-summer 2021 (phase 2). What’s happened? There are several hypotheses that can explain it. The absence of these viruses in winter has been attributed to non-pharmacological preventive measures (masks, hand washing and social distancing), however schools remained open and these measures were not applied to the little ones. In parallel, the number of children who had no contact with these viruses (debt or immune gap) increased and, as a result, RSV cases rose sharply in the summer of 2021. As the coronavirus remains a pandemic, it makes it harder for other viruses to spread. Therefore, it appears that respiratory viruses have lost their traditional seasonality, which they are likely to regain when the coronavirus is no longer pandemic but endemic and becomes a seasonal virus.
Undoubtedly, the improvement of the epidemiological surveillance system in Catalonia with sentinel centers that make it possible to follow the evolution of viruses, together with the creation of predictive epidemiological models, will help to anticipate hospital burden situations. To try to understand its behavior in the future, we started a project, coordinated by the COPEDI-CAT research group and based on a grant awarded by the Fundació La Marató de TV-3, to develop predictive epidemiological models create and understand the interaction of the different respiratory viruses with SARS-CoV-2. Sentinel breath samples are collected from various primary care centers and used by researchers from the BIOCOM-SC group at the Universitat Politècnica de Catalunya to generate information and develop models.
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