The northward march of Aedes albopictus: what the climate models projected, and where the mosquito is now

Climate-suitability modelling for Aedes albopictus in Europe dates to Caminade et al. (2012). Using high-resolution observations and regional climate model scenarios, that study found that climate conditions had become more suitable for the mosquito over central northwestern Europe (Benelux, western Germany) and the Balkans over the preceding two decades, and simulated an increased risk over northern Europe (Caminade et al. 2012).

ECDC's April 2026 update records Aedes albopictus as established in 384 regional units across the EU/EEA, including 12 of Germany's 38 units, and reports an expansion of 14 units since the June 2025 update (ECDC). The June 2025 update recorded 369 regions (ECDC).

The models were not wrong. The climate moved faster.

What the models predicted and what happened

Climate envelope models for mosquito species project establishment based on three primary variables: mean summer temperature, minimum winter temperature (which determines overwintering survival), and annual precipitation pattern. The ECDC factsheet for experts states that Aedes albopictus needs a mean winter temperature above 0°C to permit egg overwintering and a mean annual temperature above 11°C for adult survival and activity (ECDC).

The Caminade et al. models used regional climate model scenarios rather than a single emissions pathway. The study reported that suitable conditions had already extended over central northwestern Europe in recent decades, not only in a distant future window (Caminade et al. 2012).

This is not model failure. It is the observed climate running ahead of the change the models projected.

The revised picture for northern Europe

ECDC's mosquito maps record the current known distribution:

Established (April 2026): Austria, Belgium, Bulgaria, Croatia, Cyprus, France, Germany, Greece, Hungary, Italy, Malta, Portugal, Romania, Slovakia, Slovenia, and Spain (ECDC).

The transmission gap

Range expansion is necessary but not sufficient for disease transmission. Aedes albopictus needs to reach viral titres high enough to transmit dengue or chikungunya before the end of its gonotrophic cycle, which becomes increasingly likely as summer temperatures approach its dengue thermal optimum (Mordecai et al. 2017).

The Mordecai et al. 2017 thermal optimum models suggest that dengue transmission efficiency in Aedes albopictus peaks at 26.4°C and declines to zero above 31.6°C (Mordecai et al. 2017).

This is the transmission gap closing. Not quickly enough to cause mass epidemics in Germany in 2026. Quickly enough that the public-health infrastructure that would be needed to contain a 2030 or 2035 outbreak does not yet exist in northern Europe.

What this means practically

The policy question is not whether northern Europe will experience vector-borne disease transmission, it is when, and how prepared the healthcare and public-health systems will be when it arrives.

National vector-borne disease response plans should be reviewed against the current evidence as the observed distribution changes.

For European households in the affected zone, the implications are immediate and practical:

• Physical-barrier protection, window screens, door screens, bed nets, is no longer a concern for travellers to the tropics only. It is a precaution for sleeping in an unscreened room in Frankfurt, Brussels or Vienna in July.
• Standing-water elimination is the single most effective intervention at household level. Aedes breeds in containers as small as a bottle cap. The species is exquisitely adapted to the urban garden.
• If you develop dengue-compatible symptoms (sudden high fever, severe headache, retroorbital pain, myalgia) in summer months in central Europe, mention your local mosquito exposure to your GP. Differential diagnosis still tends to exclude vector-borne disease in northern European clinical settings.

The mosquito is not waiting for northern Europe to update its threat model. The model needs to update first.