Heat At Mass Events: Plan Before People Fall Sick, Says WHO

As extreme heat at mass gatherings is emerging as a significant public-health and operational risk, the World Health Organization (WHO) has said most heat-related illness at major events can be prevented or treated on site with advance planning and a well-equipped medical response system.

A new WHO evidence review, covering studies published between 1980 and 2025, documented nearly half a million medical encounters at mass gatherings, including more than 22,000 cases of heat-related illness.

More than 90% of patients in the studies reviewed could be treated at the venue when medical systems were adequately organised, reducing pressure on ambulances and nearby hospitals.

The review comes as India faces increasingly frequent and intense heat waves, making heat preparedness particularly relevant for large religious gatherings, sporting events, political programmes and cultural festivals that bring thousands of people together, often in open spaces.

“Extreme heat is an increasing threat to health, safety and operational continuity in mass gatherings and must be addressed not only as an environmental hazard but as a core operational and governance challenge,” said Dr Chikwe Ihekweazu, Executive Director, WHO Health Emergencies Programme.

The WHO review highlights that heat-related illness should not be viewed simply as an unavoidable consequence of extreme weather or large crowds. Event organisers, local authorities and health systems can reduce the risk through planning before the event, early identification of heat stress, access to shade and water, trained medical teams and rapid treatment.

The health impact of extreme heat can range from heat cramps and exhaustion to potentially life-threatening heatstroke. Older people, children, pregnant women, people with chronic illnesses and those taking certain medicines may be particularly vulnerable. At mass gatherings, these risks can be amplified by prolonged outdoor exposure, long queues, dense crowds, limited shade and inadequate access to drinking water.

India has already seen how quickly such conditions can turn deadly. For instance, when nearly a million people gathered for an event in Maharashtra in April 2023, extreme heat turned the mass gathering into a public health emergency. Twelve people died of confirmed heatstroke, with most of the deaths occurring within two hours of the crowd dispersing. The incident exposed a critical gap in preparedness: large gatherings need specific plans to deal with heat, rather than relying only on generic emergency arrangements.

The wider heat burden in India is also worrying. In May 2025, the National Human Rights Commission, citing NCRB data, reported 3,798 deaths due to heat and sunstroke between 2018 and 2022. It identified outdoor workers, elderly people, children, homeless people and economically vulnerable communities among those at greater risk.

The experience of international sporting events offers another lesson. Ahead of the Paris 2024 Olympics, athletes and climate experts raised concerns about extreme heat. Research examining the Games found that 15 of the 45 sports faced high, very high or extreme heat-stress risk. Several sporting federations used thermal indices such as the Wet Bulb Globe Temperature to assess conditions and determine appropriate precautions.

The WHO review suggests that medical preparedness at the venue can make a substantial difference. Rather than automatically transferring every patient to a hospital, trained teams can assess and treat many cases locally when appropriate facilities, equipment, cooling measures and referral systems are in place.

This can also prevent hospitals and emergency services near the venue from becoming overwhelmed.

The findings point to a shift in how organisers should approach extreme heat. Weather forecasts should be incorporated into event planning, while organisers should have clear thresholds for modifying schedules, increasing medical staffing or introducing additional cooling and hydration measures.

Heat preparedness also needs to be built into the design of the venue. Access to drinking water, shaded rest areas, ventilation, cooling stations and clearly marked medical posts can help people seek assistance before heat illness becomes severe.

Communication is another important part of prevention. People attending an event need simple information on staying hydrated, recognising early symptoms of heat stress and seeking help promptly. Volunteers, security personnel and event staff can also be trained to identify people who appear confused, weak, dizzy or unusually exhausted.

The WHO review also underscores the importance of coordination. Organisers cannot manage heat risk in isolation. Local health authorities, emergency medical services, hospitals, weather agencies and municipal bodies need to work together before and during large events, said the WHO.