Sweden's Late Season Flu Outbreak Turns Severe

Sweden's Public Health Agency recently reported several severe influenza cases have occurred in Orebro County, located west of Stockholm. Complications can occur in connection with influenza infection, but this outbreak is unusual. 

The spread of influenza A and B is estimated to continue throughout the country as of March 17, 2023.

During week #10, there was roughly the same number of cases of influenza A (385 cases) as influenza B (364 cases). 

So far, eleven newly admitted patients with laboratory-confirmed influenza have been reported in intensive care during week 10, of which six with influenza A and five with influenza B. 

The current investigation aims to assess whether there are more influenza B cases with serious complications than expected and whether there is any common contributing cause. Therefore, the Public Health Authority has asked other infection control units to investigate whether there are similar cases in other regions.

Of the 21 countries that reported sentinel primary care specimen influenza virus positivity above the 10% epidemic threshold, France, Hungary, Romania, and Slovenia reported activity above 40%.

So far, sequencing of clinical specimens from severe cases in Sweden has identified B/Victoria viruses belonging to subgroup V1A.3a.2, which is the dominant influenza type B virus circulating across Europe and the northern hemisphere 2022-23 and 2023-24 influenza vaccine strain (B/Austria/1359417/2021-like virus).

When traveling abroad, the U.S. Centers for Disease Control and Prevention suggests getting a second flu shot if visiting an area with influenza activity.

Various flu shots are available in the U.S. at health clinics and travel pharmacies.