The 2026-27 El Niño event: what should UK infection services expect?

A strong 2026-27 El Niño is developing, with potentially important consequences for infectious-disease epidemiology worldwide. For UK infection services, the principal effect is likely to arise indirectly through changes in the incidence and geographical distribution of infections among returning travellers, particularly vector-borne and enteric infections, rather than through substantial increases in infections acquired within the UK. Changes in rainfall, temperature, flooding and drought may alter transmission patterns internationally, while invasive mosquito detections, changing vector ecology and extreme weather provide smaller and less predictable potential routes to domestic effects. However, associations between El Niño and infectiousdisease outbreaks are complex, and should not be interpreted deterministically. For UK infection specialists, the appropriate response is proportionate vigilance; this includes obtaining detailed travel and exposure histories, using contemporary outbreak surveillance to inform differential diagnoses, and recognising and acting on unusual epidemiological signals promptly. El Niño should be viewed as a temporary modifier of infectious-disease risk rather than a predictor of individual outbreaks.