The Swedish Public Health Agency, together with the Örebro County Region Infection Control Unit, is currently investigating some cases of influenza B with serious complications that have been reported in the region. Those affected, under the age of 18 without an underlying disease or condition, have had complications such as myocarditis or encephalitis and have required critical intensive care. The reported complications are known to occur in connection with influenza infection, but it is unusual.
The research aims to evaluate if there are more cases of influenza B with serious complications than expected, and whether there is a common cause other than influenza infection. Therefore, the Public Health Authority has asked other infection control units to investigate if there are similar cases in other regions. They are also analyzing if there are similar accumulations of cases in other European countries, but so far nothing similar has been reported.
Virological analyzes show that all influenza B strains characterized in Sweden in the 2022-2023 season, including samples of severe cases, belong to the same genetic group of the type B/Victoria lineage that dominates in the rest of Europeand that it is included in the seasonal influenza vaccines.
Since March 14, the Örebro region has been offering free flu shots for school-age children for a limited period. Although influenza B infection can be as serious as influenza A, reports of serious cardiac or neurological complications are rare.
The European Center for Disease Prevention and Control (ECDC) has launched a alert to facilitate reporting of epidemiological information in all EU/EEA countries. It has also encouraged countries to provide information on cases of influenza B infection among children and adolescents, confirmed by laboratory and associated with serious results, through the platform PPE Pulse– an online portal for European public health authorities and partner organizations to collect, analyse, share and discuss infectious disease data for threat detection. Likewise, it has encouraged countries to determine the lineage, as well as to carry out genetic and antigenic characterization for such cases.
The body has also indicated that it would be advisable for countries shared clinical samples or virus isolates with the WHO Collaborating Center (London) for further characterization. Where available, countries are requested to provide GISAID accession numbers for sequenced isolates to allow for genomic analysis and comparisons.
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