When the United Kingdom notified WHO on 2 May 2026 of a cluster of severe respiratory illness cases aboard a Netherlands-flagged cruise ship in the Atlantic, passengers from 23 countries were on board. Within days, cases of hantavirus (Andes strain) had been confirmed in the Netherlands, South Africa and Switzerland. The ship was still at sea.
What followed was one of the most complex multi-country outbreak responses in recent years –and a direct test of the International Health Regulations (2005) (IHR), the legally binding global framework that obligates countries to prevent, prepare for, detect, report and respond to public health threats that cross borders.
Here’s how the response worked.
24/7 surveillance and detection
Even before big cross-border public health events happen, a team of WHO public health intelligence experts works around the clock to detect signals before they escalate into public health events of potential international concern. In 2025 alone, these “detectives” screened 224 000 pieces of information from both official sources, including the IHR, and media articles, resulting in 116 major public health events identified, of which 70 required immediate WHO operational response and follow-up.
Notification
From the moment WHO receives notification of a case, National IHR Focal Points and WHO engage in rapid, structured, cross-border information exchange. Speed matters: on a ship where passengers live in close quarters and then disperse to different countries, every hour of delay adds to the contact tracing challenges.
“The IHR provide clear rules and processes for reporting and managing health risks, so everyone knows what to do during a crisis,” said Demi Reurings, National IHR Focal Point for the Netherlands.
Risk assessment and medical evacuation
While the ship was still anchored off Cabo Verde, a WHO health emergency officer from the Regional Office for Africa boarded and was joined by 2 doctors from the Netherlands and an expert from the European Centre for Disease Prevention and Control. They conducted a rapid epidemiological investigation, assessed everyone on board, and confined passengers to their cabins while symptomatic individuals were immediately isolated.
WHO engaged with the shipping company to facilitate 2 medical evacuation flights to the Netherlands, transferring 2 confirmed cases directly to specialist hospitals in the Netherlands; 1 high-risk contact was transported on to Germany. This is a practical demonstration of what the IHR makes possible: time-sensitive patient transfer across borders while reducing onward exposure. In parallel, WHO facilitated repatriation flights with the European Union and ensured a critical patient transfer service provider was on standby in case any passenger or crew member developed symptoms and required urgent medical evacuation.
Contact tracing
WHO informed 12 countries whose nationals had disembarked earlier at Saint Helena, as well as the public through its Disease Outbreak News portal. That notification led directly to the identification of a case in Zurich on 6 May.
“People on the cruise ship came from all over the world, and they returned to countries from all over the world. The ability of all the governments to come together and follow up on those contacts has actually been amazing,” said Boris Pavlin, WHO epidemiologist.
Laboratory coordination
Laboratory testing in South Africa confirmed hantavirus infection in a critically ill patient who was on the boat days before. WHO then coordinated a multi-country sequencing effort, comparing Andes virus genomes from across the cluster to establish how the outbreak originated and spread.
“This analysis turns multi-country laboratory data into actionable public health intelligence to guide quarantine protocols, medical evacuations and international contact tracing,” said Karen Nahapetyan, Laboratory Specialist at WHO/Europe.
Disembarkation in Tenerife
Before the ship arrived in Tenerife on 10 May, WHO provided Spanish authorities with step-by-step operational guidance for the safe disembarkation and onward management of all passengers and crew – covering infection prevention, screening advice and risk communication.
Twenty-three countries were involved in the operation. All passengers have since returned home and are under 42-day monitoring, according to WHO recommendations.
The bigger picture
“While this is a serious incident, WHO assesses the public health risk as low,” said WHO Director-General Dr Tedros Adhanom Ghebreyesus. “It also shows why the International Health Regulations exist, and how they work.”
“This outbreak reminds us that health security is not built during a crisis – it’s built before one,” said Dr Hans Henri P. Kluge, WHO Regional Director for Europe. “The IHR gave us the framework. Collective action gave us the response.”
The hantavirus cluster on the cruise ship, the MV Hondius, is the first documented outbreak of this virus on a ship. It is unlikely to be the last time that a pathogen tests the international health architecture at sea. The response demonstrated that when countries notify quickly, share data openly and act in solidarity, the system holds and lives are saved.
“Solidarity is our best immunity,” said Dr Tedros. “It is only when we support each other that we can respond effectively.”