Flu season in Sweden
Current flu activity in Sweden — based on ECDC ERVISS weekly data, set against the parallel COVID-19 and RSV trajectories.
Current situation: Influenza
In week 15 of 2026, activity of influenza (seasonal flu) in Sweden is low. The trend — derived from clinical surveillance — is falling. Over a four-week comparison, a clear decline is visible.
The classification is based on the ECDC ERVISS weekly reports, drawing on sentinel and virological data from the Public Health Agency of Sweden (Folkhälsomyndigheten); where national indicators are stale, the EU median is used as a fallback. Seasonally, infection waves in Sweden typically peak between January and March; activity is usually markedly lower during the summer months. How severe a given season becomes depends on the circulating virus variant and the population's immune status, among other factors.
Data sources and methodology
The current picture for Sweden is built on the European Respiratory Virus Surveillance Summary (ERVISS), published weekly by the European Centre for Disease Prevention and Control (ECDC). Folkhälsomyndigheten is the national public-health authority that feeds ERVISS with sentinel primary care and virology data. Sweden does not always report ILI consultation rates to ERVISS; when national ILI is missing we fall back to the EU median so the signal remains comparable.
ECDC ERVISS
ERVISS is ECDC's weekly pan-European surveillance summary for influenza, SARS-CoV-2 and RSV. National authorities — in Sweden's case Folkhälsomyndigheten — submit harmonised indicators every week, which ECDC publishes in a standardised dataset on Thursdays. Using ERVISS rather than each country's native portal ensures cross-country comparability.
ILI / ARI consultation rates and positivity
Folkhälsomyndigheten operates a sentinel network of general practices that report weekly rates of patients consulting for influenza-like illness (ILI) or acute respiratory infection (ARI). A subset of patients is swabbed and tested by reference laboratories, producing pathogen-specific positivity rates for flu, SARS-CoV-2 and RSV.
Why this source
Combining consultation incidence with virological positivity yields a pathogen-specific weekly incidence signal (ILI × positivity / 100). This is the standard European methodology and provides a more robust view than either indicator alone — consultation rates capture illness burden, positivity confirms which pathogen is driving it.
Qualitative classification
The “low”, “moderate” and “high” categories follow seasonal reference values and epidemiological thresholds calibrated to match our classifications for other countries. The ILI × positivity / 100 product is scaled to comparable thresholds using a divisor of 3, which aligns European sentinel peaks with the consultation-equivalent scale used elsewhere. Data refreshes weekly when ECDC publishes the latest ERVISS update, typically on Thursdays.
Frequently asked questions
When is flu season in Sweden?
Swedish flu seasons typically build through December and peak between January and March, somewhat later than central European peaks. The precise window shifts each year with the dominant influenza subtype and population immunity. Folkhälsomyndigheten's weekly reports describe the season in terms of rising, peak, declining, and low-activity phases rather than precise onset dates.
Who runs flu surveillance in Sweden?
Sweden's Public Health Agency, Folkhälsomyndigheten, runs national influenza surveillance. It combines mandatory reporting of laboratory-confirmed cases, the Webbsök web-search signal, sentinel physician reports, and the Svebar laboratory network. Weekly summaries are published openly and also reported to ECDC for inclusion in the European ERVISS platform.
How does Sweden report into European flu data?
Folkhälsomyndigheten transmits Sweden's weekly influenza, SARS-CoV-2, and RSV indicators to ECDC, where they appear in ERVISS — the European Respiratory Virus Surveillance Summary. This places Sweden's trajectory next to other Nordic countries (Norway, Finland, Denmark) and the rest of the EU/EEA using harmonised tiering. That harmonisation is what makes cross-border comparisons meaningful.
How does Sweden's flu season compare to Germany's?
Swedish peaks are generally a few weeks later than German peaks, and the whole winter curve sits slightly shifted toward February and March. This reflects Sweden's latitude and indoor-contact patterns. Because both countries report into ERVISS with the same methodology, the relative timing and intensity of their peaks are directly comparable in ECDC's published dashboards.
How does Folkhälsomyndigheten classify flu intensity?
Folkhälsomyndigheten classifies activity qualitatively — low, medium, high, very high — using established reference thresholds. These reflect historical ranges of consultation rates, positivity, and, where available, hospitalisation signals. The purpose is to describe whether the week's load is normal, elevated, or exceptional for the season, not to imply a precise incidence figure.
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