Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea

Grounds assessments

activeLa Réunion 2026 chikungunya outbreak will exceed 100,000 cumulative confirmed/suspected cases by September 2026 (from approximately 47,000 as of Apr 22 2026), one of the largest CHIK events in Indian Ocean island history.60%activeAutochthonous chikungunya transmission will be documented in at least one additional Chinese province beyond Guangdong during the 2026 warm season (May–October), confirmed by national health authority or peer-reviewed publication.50%activeLa Réunion 2026 chikungunya outbreak will exceed 100,000 cumulative reported cases by August 31 2026, based on the 47,500+ case trajectory as of April 2026 and the historical precedent of the 2005-2006 Réunion epidemic reaching 266,000 cases over a longer surveillance period, given that 2026 surveillance capacity and reporting speed are substantially higher than 2005.60%activeECDC will issue a rapid risk assessment or seasonal preparedness alert specifically addressing La Réunion and/or Mayotte chikungunya importation risk for Mediterranean Europe (Italy, Spain, France, Greece) before the 2026 vector season peak (by July 1, 2026), given the 47,500+ case scale of the La Réunion outbreak and established Aedes albopictus populations in Southern Europe.50%resolvedLa Réunion chikungunya outbreak will sustain >10,000 cumulative reported cases through at least July 31 2026, maintaining active seeding pressure on metropolitan France during the peak Aedes albopictus transmission window.70%activeViremic travelers from La Réunion will seed at least one documented autochthonous chikungunya cluster (≥2 locally-acquired cases) in Italy, Spain, or Greece during the 2026 vector season (July–October), given the scale of the current La Réunion outbreak (47,500+ cases) and established Aedes albopictus populations in Mediterranean Europe.50%activeFirst confirmed autochthonous dengue or chikungunya transmission in the UK, Netherlands, Belgium, or Germany will be documented during the 2026 or 2027 Northern Hemisphere transmission season (June–October).30%activeSpain will document ≥500 autochthonous chikungunya cases in the 2026 vector season (April–October 2026), confirming the expanded transmission window as epidemiologically significant and establishing a quantitative baseline for the 2027 autochthonous cycle.50%

Evidence content

Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea — research event update (updated 2026-04-13T21:05)

Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea

Field	Value
date	2026-04-13
event_type	who-don
headline	Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea
research_domain	generic
scope	arbovirus
source_meta	{"source":{"sourceId":"who-don","name":"WHO Disease Outbreak News","tier":"T1","url":"https://www.who.int/emergencies/disease-outbreak-news","documentUrl":"https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON567","documentTitle":"Chikungunya - La R\u00e9union and Mayotte"},"hypothesisLinks":[{"hypothesisId":"hyp:arbovirus:2027-10-31:2026-04-13","direction":"supports","weight":0.419}],"flags":[],"direction":"supports","relevanceScore":0.419,"publishedAt":"2025-05-12T15:53:32.000Z","metadata":{"listingUrl":"https://www.who.int/emergencies/disease-outbreak-news","extractionMethod":"who-don-api","articleExtractionMethod":"dom-content","formattedDate":"12 May 2025","emergencyEventUrl":null,"regionscountries":["1c8e9fa9-fd11-40bb-bf06-0ca52d115683"],"language":"en","extractedTitle":"Chikungunya - La R\u00e9union and Mayotte","claimLevel":true,"reportType":"disease_outbreak_news","scopeHints":["arbovirus"],"claimRole":"case_count","claimOrdinal":0,"claimFingerprint":"bcb8e63576186e4ac536b0ea15d089e52528711cf13abbbad7d5e51e77a6951d","signalClass":"case_count","pathogens":["chikungunya"],"hosts":[],"places":[],"country":null,"location":"","canonicalPlaceIds":[],"lineages":[],"mutations":[],"resistanceGenes":[],"counts":{"cases":500,"deaths":0,"samples":0},"studyType":null,"certainty":null,"classification":{"strategy":"keyword-v1","scopeId":"arbovirus","hypothesisMatches":1,"scopeRelevance":0.07692307692307693}}}
source_url	https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON567
summary	Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated deaths have been reported as of 4 May 2025, with sustained high transmission across the island.

Epidemiology

Cases: 500
Deaths: 0
Samples: 0

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Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea — research event update (updated 2026-04-13T21:05)

Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea

Field	Value
date	2026-04-13
event_type	who-don
headline	Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated dea
research_domain	generic
scope	arbovirus
source_meta	{"source":{"sourceId":"who-don","name":"WHO Disease Outbreak News","tier":"T1","url":"https://www.who.int/emergencies/disease-outbreak-news","documentUrl":"https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON567","documentTitle":"Chikungunya - La R\u00e9union and Mayotte"},"hypothesisLinks":[{"hypothesisId":"hyp:arbovirus:2027-10-31:2026-04-13","direction":"supports","weight":0.419}],"flags":[],"direction":"supports","relevanceScore":0.419,"publishedAt":"2025-05-12T15:53:32.000Z","metadata":{"listingUrl":"https://www.who.int/emergencies/disease-outbreak-news","extractionMethod":"who-don-api","articleExtractionMethod":"dom-content","formattedDate":"12 May 2025","emergencyEventUrl":null,"regionscountries":["1c8e9fa9-fd11-40bb-bf06-0ca52d115683"],"language":"en","extractedTitle":"Chikungunya - La R\u00e9union and Mayotte","claimLevel":true,"reportType":"disease_outbreak_news","scopeHints":["arbovirus"],"claimRole":"case_count","claimOrdinal":0,"claimFingerprint":"bcb8e63576186e4ac536b0ea15d089e52528711cf13abbbad7d5e51e77a6951d","signalClass":"case_count","pathogens":["chikungunya"],"hosts":[],"places":[],"country":null,"location":"","canonicalPlaceIds":[],"lineages":[],"mutations":[],"resistanceGenes":[],"counts":{"cases":500,"deaths":0,"samples":0},"studyType":null,"certainty":null,"classification":{"strategy":"keyword-v1","scopeId":"arbovirus","hypothesisMatches":1,"scopeRelevance":0.07692307692307693}}}
source_url	https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON567
summary	Chikungunya - La Réunion and Mayotte. In La Réunion, over 47 500 cases and twelve associated deaths have been reported as of 4 May 2025, with sustained high transmission across the island.