Swiss heatwaves linked to around 600 excess deaths

Around 600 additional deaths were recorded in Switzerland between June and September 2026, as the country endured its hottest summer since measurements began in 1864. Weekly mortality figures from the Federal Statistical Office show a sustained rise that coincided with two periods of extreme heat.

The first wave, which struck at the end of June, caused the sharpest increase. A second, longer episode arrived in early August after a brief break in July. Together, the events pushed summer mortality above expected levels across the country.

The estimate places the human cost of the summer above the Swiss Tropical and Public Health Institute’s recent seasonal average of around 500 heat-related deaths. It remains well below the roughly 1,400 additional deaths recorded during the severe summer of 2003, but the comparison offers little comfort to public health officials facing more frequent hot spells.

The figures also show why heat cannot be treated solely as a weather story. Its effects reach hospitals, care facilities, workplaces and households, particularly when high temperatures persist overnight and limit the body’s ability to recover.

The first heatwave of the summer proved the most lethal, a pattern Martina Ragettli, an epidemiologist at the Swiss Tropical and Public Health Institute, says is common. People have not yet adjusted physiologically or behaviourally to high temperatures when the first major hot spell arrives.

“At the beginning of summer, we are not yet adapted to the heat,” Ragettli told SRF. As the season continues, the body gradually develops greater tolerance. People also learn to change routines, drink more water, limit exertion and seek cooler places.

That adjustment offers only partial protection. The June heatwave arrived early, when households, employers and care providers may not have activated their full heat response plans. High temperatures can worsen cardiovascular and respiratory conditions, increase dehydration and place additional strain on the body.

The timing also matters because Switzerland’s heat exposure varies sharply by setting. Dense urban neighbourhoods retain heat after sunset. Outdoor workers face direct exposure during the day. Residents of care homes and people living alone may need help to recognise symptoms before their condition deteriorates.

The second heatwave exposed a rise in mortality among people under 65, a finding that has drawn particular attention from Swiss researchers. Older people remained the most affected group, as expected, yet the August increase among younger adults showed that vulnerability extends well beyond retirement age.

Ragettli points to a possible change in daily routines. The August heatwave arrived as the holiday period ended and people returned to construction sites, shops, offices and care facilities. Many resumed commuting and outdoor work, with fewer opportunities to stay in cooler environments.

“It was back to everyday life, and people had fewer opportunities to protect themselves from the heat,” Ragettli said. She stressed that this is only one hypothesis. The duration and intensity of the August event may also have contributed, and the available data cannot establish a single cause.

Outdoor workers, delivery staff, commuters and people without access to air conditioning can face prolonged exposure. Employers must manage rest periods, shade, hydration and working hours when forecasts show dangerous temperatures. Individuals with heart or lung conditions also face elevated risks, even if they are far younger than 65.