El Niño

El Niño is the warm phase of the El Niño-Southern Oscillation. This natural cycle links unusual warming in the central and eastern equatorial Pacific with changes in the atmosphere. It can shift rainfall and temperature across many regions, although the direction and strength of those effects differ by place and season.

Those shifts can affect food and water security, place pressure on health services and change conditions for vector-borne or waterborne disease. Public-health agencies use seasonal climate forecasts to plan surveillance, staffing and supplies before local effects arrive. The link is indirect: El Niño is a climate pattern, not an infection. Its health importance comes from changing the environments in which hazards such as Dengue can spread or become harder to control.