Encounters in the third phase for childhood viruses?

The respiratory syncytial virus (RSV) is the main cause of acute bronchiolitis, the most frequent respiratory infection in childhood and the main cause of admissions in children under one year of age.

An RSV epidemic occurred annually in Catalonia between November and March, with an epidemic peak at the end of December, before the first cases of influenza were detected.

This pattern was constant until the arrival of the SARS-CoV-2 coronavirus in March 2020. At that time one of the first measures taken was the closure of schools.

It was believed, based on the data we had on the flu, that the child population could be the most contagious for covid-19.

It was shown that, contrary to expectations, adults were the main responsible for the transmission of SARS-CoV-2.

After the first pandemic wave,

The arrival of the first pandemic autumn-winter (2020-2021) generated great uncertainty about what would happen to the flu and RSV.

There was a surprising reduction in the circulation of these viruses compared to other years, until in the spring-summer of 2021 they began to appear outside their usual season (phase 2).

What had happened?

There are several hypotheses that can explain it.

The non-appearance of these viruses in winter was attributed to non-pharmacological prevention measures (masks, hand washing and social distance), however, schools remained open and these measures were not applied to the little ones.

In parallel, the number of children who had not had contact with these viruses (debt or immune gap) increased, and as a consequence, in the summer of 2021, RSV cases increased sharply.

Also, as the coronavirus remains a pandemic, it makes it difficult for other viruses to circulate.

Therefore, it seems that respiratory viruses have lost their traditional seasonality, which they will probably recover when the coronavirus ceases to be pandemic to be endemic and becomes a seasonal virus.

Undoubtedly, the improvement of the epidemiological surveillance system in Catalonia with sentinel centers, which allow the evolution of viruses to be followed, together with the creation of predictive epidemiological models, will help to anticipate situations of hospital burden.

To try to understand its behavior in the future, we have launched a project, coordinated by the COPEDI-CAT research group, based on a grant awarded by the Fundació La Marató de TV-3, to create predictive epidemiological models and understand the interaction of the different respiratory viruses with SARS-CoV-2.

Sentinel respiratory samples are collected in different primary care centers and are used to generate information and develop models by researchers from the BIOCOM-SC group of the Universitat Politècnica de Catalunya.

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