Swedish health officials are investigating a cluster of severe influenza B infections in children and adolescents, some of whom had complications, including myocarditis and meningoencephalitis, the European Centre for Disease Prevention and Control (ECDC) said in its most recent weekly communicable disease update.
The cases have been reported in previously healthy kids, and some children have required intensive care unit (ICU) admission. Health officials are assessing if the pattern exceeds expected levels.
Sweden's Public Health Agency, in its latest weekly flu update, said the cases occurred in Orebro County, located in the central part of the country about 130 miles west of Stockholm.
Cases rising for a month
Influenza B activity typically picks up later in the flu season, and the ECDC said flu B viruses have been on the rise in Sweden since about the middle of February. Two suspected cases and one confirmed case have epidemiologic links. Sequencing suggests that the Victoria lineage virus is similar to those circulating in other parts of the world. It's not known how many kids were vaccinated against flu or had COVID-19 before they got sick with flu B.
The ECDC said reduced flu circulation and exposure to the virus in the past few seasons may have lowered population immunity. "So it is important to remain vigilant for signals of increased severity in different population groups," it said.
It is important to remain vigilant for signals of increased severity.
Influenza B infections are known to be more common in children and can cause complications, resulting in hospitalization or death. In 2019, an early-season spike in influenza B activity in Louisiana resulted in a number of hospitalizations, one of them fatal.