Decreased prevalence of influenza virus and RS virus after severe winter season – Public Health Agency

Public Health Agency observation shows that this year’s influenza season was widespread and until the beginning of March was dominated by influenza A, followed by a period in which influenza B dominated. The prevalence of influenza A reached a high level in December 2022 with more confirmed cases and ICU patients per week. From February to April, the number of influenza B cases rose, and during this period, many patients newly admitted to intensive care with influenza A and B were reported.

– The prevalence of both influenza A and B is now believed to have dropped to a low level, and the epidemic is believed to be over for the season. During December 2022, we faced a difficult situation, when influenza, RS virus and covid-19 reached high levels at the same time. During each period of increased infection spread, there are people who become seriously ill, says Anasara Carnahan, an epidemiologist and researcher at the Public Health Agency, but this winter was the first time we had a simultaneous peak with all three diseases.

This year’s RS virus season reached high levels of transmission in December 2022 and January 2023. More patients were hospitalized with RS virus infection than in pre-pandemic seasons. Just over 30 per cent of those in intensive care were children under the age of 1. The prevalence of RS virus has decreased since the turn of the year and cases have been at a low level since the end of April and the season is considered to be over.

– There were two winters with many sick young children, which is likely related to the fact that there were few RS cases during the first winter of the epidemic. There have been many young children who have not yet been infected with RS, Anasara Karnahan says, and therefore have a high susceptibility to infection.

The spread of covid-19 is still ongoing and has been dominated by various sub-variants of the omicron virus variant for a long time. During December 2022, the spread of COVID-19 increased sharply again in Sweden. The number of confirmed cases, as well as the number enrolled in inpatient and intensive care care, was at its highest level at the turn of the year, but has since declined and has remained at the same level since March. The spread of COVID-19 varies between regions and is expected to continue even during the summer months. People 80 years of age or older and people who live in a SÄBO (private residence for the elderly), an additional dose of the covid-19 vaccine is recommended before summer.

Relatively many cases of winter sickness are still being reported, but in recent weeks they have gradually decreased and the assessment is that the peak has passed but the season is not over yet. This year’s season is very similar to the 2021-2022 season which was intense with a high number of reported cases.

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