Heat linked to an estimated 1,257 deaths in Switzerland this summer

An estimated 1,257 people died because of heat in Switzerland from May to August 2026, according to a preliminary assessment by the Swiss Tropical and Public Health Institute. Commissioned by the Federal Office of Public Health, the report puts the heat toll at 5.5% of all deaths during those four months, equivalent to 14 deaths per 100,000 people.

The estimate comes after the country’s hottest summer since records began, which surpassed even 2003. Researchers calculated a 95% confidence interval of 1,053 to 1,479 deaths, reflecting the statistical uncertainty around the figure. The toll is an estimate of deaths attributable to heat, not a tally of individual death certificates that name heat as the confirmed cause.

The preliminary scale of the finding puts heat-related mortality among the significant public-health consequences of the 2026 summer. The report’s results draw on temperature records from MeteoSwiss and preliminary mortality data from the Federal Statistical Office.

About 85% of the estimated deaths were among people aged 75 or older. The age profile makes the toll especially relevant to older people and the institutions that care for them during periods of high temperatures.

The report links most of the estimated deaths to hot or very hot days. About seven in ten were attributed to such days. Researchers associated 485 deaths with daily mean temperatures of at least 25°C but below 27°C, and 400 deaths with daily means of 27°C or higher. The remaining estimated deaths were associated with more moderate heat.

These figures describe a statistical relationship between temperature and mortality across the period, rather than a list of individuals whose deaths were individually certified as heat-caused. The concentration of deaths among older people, alongside the temperature breakdown, shows why the effects of sustained heat matter beyond the hottest days on the thermometer.

The 2026 estimate is broadly similar in scale to Switzerland’s 2003 heat toll, once statistical uncertainty is considered. The comparison remains provisional because the periods differ: the current estimate covers May through August, while the historical figures for 2003 include September.

Researchers combined daily mean temperatures recorded by MeteoSwiss with preliminary mortality figures from the Federal Statistical Office. Their model accounts for heat’s delayed effects over seven days, so its estimate reflects mortality patterns that can follow hot weather rather than only deaths on the hottest day itself.

September was excluded from the preliminary 2026 calculation because mortality data for that month were too incomplete. The report therefore presents a four-month estimate, not a full summer total. The Federal Statistical Office’s mortality monitoring identifies periods of excess deaths, while the Swiss estimate uses temperature data to assess deaths attributable to heat.

Final figures are due in spring 2027, with September included and results broken down by age, sex, region and canton. The completed assessment will also be compared with the Federal Statistical Office’s mortality monitoring, which tracks periods of excess mortality but does not use temperature data to attribute deaths to heatwaves.

A study of 615 nursing homes in Ontario, Canada, offers one possible point of comparison for protecting older people. Published in JAMA Internal Medicine, it found that extreme heat was associated with an 11% rise in the odds of death in homes without air conditioning, compared with a 3% rise in homes with it. The findings suggest cooling may reduce deaths, though the Canadian results do not transfer directly to Switzerland.

For Switzerland, the final report will provide a more complete view of the 2026 summer and show how estimated heat-related mortality varied across the country’s population and cantons.