Rapid Surge in Influenza Cases in Sweden as K-Variant Spreads

Influenza cases in Sweden have more than doubled over the past two weeks, marking a swift increase in infections as the country heads into the holiday season. According to the Public Health Agency of Sweden, the reported cases rose from 403 to 808 in just two weeks, driven predominantly by the K-variant of the influenza A virus H3N2. This rapid escalation is accompanied by growing pressure on health services, with a rise in severe cases seen alongside the increasing infections.

Deaths linked to influenza increased from 5 to 14 and intensive care admissions rose from 7 to 12 during this period. Epidemiologist AnnaSara Carnahan noted this pattern of sudden case growth is typical at the epidemic onset, adding that the rise is expected to continue through the Christmas holidays, although the peak timing remains uncertain. She also emphasized that while the vaccine's effectiveness against the K-variant is unclear, some protection, especially against severe illness, is anticipated.

This year’s influenza surge is stronger compared to last season, which saw only 64 and 110 cases in weeks 48 and 49 respectively. Additionally, more than 534,000 people reported sick leave in November, an increase from October’s 501,000. Seasonal winter vomiting disease has also begun circulating, with community spread indicated by health-related web searches hitting thresholds for increased calicivirus.

Swedish authorities recommend good hand hygiene and staying home when unwell to reduce spread. Unlike the UK, which has advised outdoor mask use, Sweden has not imposed similar measures. Deputy State Epidemiologist Klara Sondén highlighted the unpredictability of the outbreak's full extent given last year's relatively mild season.

The ongoing influenza increase reflects a significant public health challenge as Sweden prepares for winter gatherings, emphasizing continued vigilance and protective behaviors to mitigate transmission.