The hantavirus outbreak aboard a cruise ship off the coast of West Africa is not another Covid-19. But it does raise an unsettling concern: six years after the pandemic exposed profound failures in global co-operation, the world still struggles to manage health threats coherently and collectively.

Hantavirus is a severe and potentially lethal disease. Health officials have confirmed at least eight cases linked to the cruise outbreak, including three deaths and a patient who is critically ill.

Transmission of the disease is usually contained because people contract the virus through exposure to infected rodent droppings, urine or saliva. But authorities have identified a rare strain on this ship, originating in the Andes region of South America, that can spread from person to person, though typically only through close and prolonged contact. Unlike coronavirus, which spreads efficiently through the air, Andean hantavirus does not pose the same broad public risk. The danger is real, but it remains limited.

The Hondius, a Dutch-flagged cruise ship, departed from Argentina on April 1, stopping at remote destinations in the South Atlantic. A large group of passengers disembarked on the island of St Helena after the first death linked to the outbreak, later returning to their home countries. The public health challenge is therefore no longer confined to one ship; it now depends on whether national authorities can identify, monitor and care for exposed travellers scattered across borders.

By the time the outbreak was widely reported, the cruise ship was off the coast of Cape Verde in West Africa. Authorities there did not permit general disembarkation, citing limited health-system capacity and concern about exposing the local population. Spain has now agreed to receive the ship in the Canary Islands. Several patients have been medically evacuated to Europe, while other passengers will be repatriated to their home countries.

The result is a fragmented international response as passengers disperse across borders. The World Health Organisation has recommended active monitoring for 45 days, but it remains unclear whether quarantine, isolation, testing and medical follow-up will be applied consistently. What we do know is that hantavirus disease can progress rapidly. If symptoms worsen and lung complications develop, the disease can be lethal. There is no specific antiviral cure, but prompt, intensive supportive care can be life-saving.

The scene aboard the Hondius is uncomfortably familiar. Early in the Covid pandemic, cruise ships became floating symbols of international paralysis. Passengers and crew were trapped aboard the Diamond Princess, quarantined off Japan in 2020, while governments argued over who was responsible for them. Similar episodes unfolded around the world as ports closed and countries denied entry, stranding travellers.

Those failures were supposed to change the way the world responds to health emergencies. With strong US support, the WHO adopted amendments to its governing rules for cross-border disease threats. (I was on the WHO review committee for those changes.) The reforms were intended to strengthen transparency, improve co-ordination and better protect travellers. The regulations also maintain a longstanding rule regarding ships and aircraft: states should not deny vessels entry into ports or prevent disembarkation, subject to limited public health exceptions.

The hantavirus outbreak is showing in real time that even strengthened global health rules remain fragile. The WHO sought to co-ordinate the response by issuing outbreak alerts, sharing information and recommending monitoring of exposed passengers. But the agency lacks authority to ensure compliance with international rules. It cannot compel countries to permit disembarkation, harmonise quarantine policies or share responsibility for exposed travellers.

Cruise ships uniquely expose the structural weaknesses of managing infectious diseases aboard crowded vessels. They compress globalisation into a single floating environment: multinational passengers, private operators, overlapping jurisdictions and long-distance travel. It is not just hantavirus. Influenza, measles, norovirus and other infectious pathogens can spread rapidly aboard crowded vessels. Once an outbreak emerges at sea, responsibility quickly becomes diffuse and contested.

The political tensions surrounding the WHO further complicate the situation. The reforms it adopted were intended to avoid another chaotic maritime crisis. While the Biden administration strongly advocated for new rules, President Donald Trump withdrew the United States from the organisation and formally rejected the amendments.

As the world confronts another cross-border outbreak, political support for international co-operation is weakening.

Meanwhile, negotiations over a new WHO pandemic agreement have stalled in Geneva. Later this month, the World Health Assembly is expected to give countries another year to complete that work. But the world may not have the luxury of waiting if a more transmissible pathogen emerges.

Media coverage of the outbreak risks overstating the epidemiological threat. The world is not facing another Covid-19. But the episode should shake political leaders from their complacency.

Most outbreaks — whether a novel influenza, a coronavirus or a haemorrhagic fever like Ebola — never become global catastrophes. But they reveal how quickly fear and politics can overwhelm rational public health responses.

The greatest danger aboard the Hondius may not be that this virus becomes the next pandemic. It is that, after Covid-19 exposed the catastrophic costs of delay, denial and disjointed global action, the world still appears dangerously willing to repeat the same mistakes.

• Lawrence O Gostin is professor of global health law, Georgetown University, and directs the World Health Organisation Centre on Global Health Law