NewsDesk @bactiman63

The Sweden Public Health Agency, together with the Infection Control Unit in the Örebro County region, is investigating a few cases of influenza B with serious complications that have been reported in the region.

generic influenza virion
3D influenza/CDC

The cases, which have been among people under the age of 18 without an underlying disease or condition, have been very seriously ill with complications such as myocarditis or encephalitis.

It is already known that the reported complications can occur in connection with influenza infection, but this is unusual.

The investigation aims to assess whether there are more influenza B cases with serious complications than expected and whether there is any common contributing cause in addition to the influenza infection. 

Therefore, the Public Health Authority has asked other infection control units to investigate whether there are similar cases in other regions. The Public Health Authority is also investigating whether there are similar accumulations of cases in other European countries, but nothing of the sort has been reported so far.

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Virological analyzes show that all Swedish characterized influenza B strains in the 2022–2023 season, including samples from severe cases, belong to the same genetic group of lineage type B/Victoria that dominates in the rest of Europe and that is included in the season’s influenza vaccines.