Sarah Newey Global Health Security Correspondent. Paul Nuki Global Health Security Editor

Hantavirus is widespread in rats and known to spread human-to-human given the right set of circumstances.

The biggest outbreak occurred during the Korean War over 70 years ago when some 3,200 US servicemen were infected, killing hundreds.

A more recent 2018/19 outbreak in a village in Chubut Province, Argentina, resulted in 34 confirmed infections and 11 deaths. 

Researchers found that the virus had been spread at a birthday party and then a wake for one of the victims and was susceptible to “super-spreader” type events.

So how is it that the world has seemingly been blindsided by the latest outbreak, and why are there no vaccines, treatments or even rapid diagnostic tests available?

Afterall, Andes Hantavirus – unlike Covid 19 – is no mystery Disease X. It’s a known threat and in retrospect looks like an accident waiting to happen.

“When I heard about the outbreak, the first thing I looked for was a vaccine on the shelf, a diagnostic test, or a treatment,” said Prof Devi Sridhar, chair of Global Public Health at the University of Edinburgh. “But we don’t have any of that. The lack of countermeasures is our greatest weakness.”

The gap is all the more surprising given that the Andes virus is listed as a “high priority” pathogen by the World Health Organization (WHO).

As far back as 1997, a WHO working group noted in a report that hantavirus infections “are among the important emerging and re-emerging communicable diseases that are of increasing concern in international public health.

“Based on the current global epidemiological situation of the disease, the prevention and control of hantavirus infections should be a high priority for Member States and WHO,” it added. 

While money has been spent researching hantaviruses, the total outlay has been modest.

Just $7.5 million was spent on research and development in 2024 for all hantaviruses, according to a scorecard from the International Pandemic Preparedness Secretariat. 

This is by far the smallest sum of the 13 pathogens they tracked – the next lowest was MERS, with $29m.

The highest, by contrast, was Covid-19, with $15 billion, and then Ebola with $488 million. 

As the victim of the most serious hantavirus outbreak to date, the US military was in the lead regarding research into the Andes version of the virus.

It was researchers from the US Army Medical Research Institute of Infectious Diseases at  Fort Detrick, Maryland, who conducted a study which showed the virus was susceptible to “super-spreader” events in the right social circumstances.

“Our findings traced the first person-to-person transmission event to a birthday party with approximately 100 guests,” said the researchers, whose work was published in the New England Journal of Medicine in 2020.

“It appears that inhalation of droplets or aerosolised virions may have been the routes of infection,” said the researchers.

The US military was also leading the way on vaccine research but, say researchers, finding the money to progress their work has proved difficult.

The journal Nature this week interviewed Jay Hooper, Chief of the Molecular Virology Branch at the US Army Medical Research Institute at Fort Detrick, who has studied Hantavirus for over 30 years.

“Because these viruses are rodent-borne and pose a risk to troops on the ground, the military has long wanted a vaccine,” Mr Hooper said.

He noted that progress had been made, with phase 1 clinical trials of vaccines for Andes virus and two other strains successfully completed, but that there was still much work to be done.

“Because human cases of Andres virus are rare and geographically scattered, there is no obvious region to run a classic phase 3 efficacy trial,” he noted.

“Right now, we are pushing from the research side, but there is no strong external pull, so progress is slower than it could be. It is frustrating – like pushing a rock up a hill for years.”

Although the researchers at the high security facility at Fort Detrick have worked with the virus, there is no suggestion that this is the source of the outbreak, despite social media claims to the contrary.

Dr Scott Weaver, the director of the Global Virus Network at the University of Texas Medical Branch, has a similar story.

In 2021, his lab was awarded a series of grants through the Centres for Research in Emerging Infectious Diseases (CREID) network, ranging from $500,000 and $1.7 million, mainly to work on rodent-borne diseases. 

One of the pilot projects was designed to better understand how hantavirus passes between rats and to people in Argentina. But it ended when the US National Institutes of Health decided under President Trump that all research under the CREID network was “unsafe” and cut the entire programme.

“I don’t think anyone should be blamed for not foreseeing this particular risk on a cruise with Andes virus, it came out of the blue,” Dr Weaver said. “But I am worried that the funding and perceived importance of research and development and international collaboration is declining, especially in the United States.”

“We’ll continue to have lots of blind spots if we just terminate and abandon this kind of research and hope for the best … Unfortunately, we’re going in the wrong direction.”

Financial constraints have also hampered vaccines, which are under development at organisations including the UK Health Security Agency and Bath University.

On the other side of the world, in South Korea and China, vaccines have been developed – but for a different strain of the virus.

The first known hantavirus was formally identified in the country in 1978, in rats close to the Hantan River. Subsequently named Hantaan virus, this is one of the ‘Old World’ hantaviruses found in Asia and Europe, which primarily cause bleeding disorders and kidney dysfunction.

They are less fatal than the ‘New World’ strains found in the Americas, like Sin Nombre virus and Andes virus.

Although a vaccine for Hantaan virus has been used in South Korea since 1990, the inactivated immunisation is considered only mildly effective, with roughly a 58 per cent efficacy against disease. 

The country still sees between 300 and 600 cases every year, while nearby China sees up to 10,000. 

At the Korea University’s Vaccine Innovation Centre, researchers have been collaborating with Moderna since 2023 through the company’s mRNA Access Program to improve the Hantaan virus immunisation and create an Andes virus shot. 

Prof Woo Joo Kim, the director of the Vaccine Innovation Centre and colleague of the late Dr Ho Wang Lee, who first sequenced hantavirus in 1978, said their ultimate aim is to develop a “pan-hantavirus” vaccine that’s capable of protecting against all strains of the bug. 

For now, an early mRNA vaccine candidate has been shown to prevent hantavirus infections in mice. Yet Prof Kim is not confident about whether they’ll be able to test it in trials. 

“Money is the big obstacle to develop an mRNA pan-hantavirus vaccine,” he said. “There’s no interest from major manufacturers, they’re just keen on blockbuster diseases, and no interest from big governments … Our target goal is to launch clinical trials for our first hantavirus vaccines in 2028, but will we get the money? I don’t know.”

Coalition of Epidemic Preparedness Innovations (Cepi), which funds vaccine development for priority pathogens, is the sort of body that could fund such research.

Under its “100 Day Mission”, established after the Covid-19 pandemic, it is seeking to have vaccines ready for deployment within 100 days of an outbreak for all the major pathogens with pandemic potential. 

Although the Cepi program is well underway, it is still early days, and so far it has not turned its attention to hantavirus vaccine.

The fact is there are thousands of pathogens in the wild with pandemic potential and covering them all off will take many decades.

Yet the hantavirus outbreak on MV Hondius is a reminder of the risks posed by these disease blind spots. 

A team of experts at the US Centres for Disease Control (CDC) that was tasked specifically with preventing disease outbreaks on cruise ships was fired last year, amid a larger gutting of the agency. 

The unit, known as the Vessel Sanitation Programme, had historically assisted authorities in managing large outbreaks of contagious viruses on board passenger cruises. 

“I hope it’s a wake up call to people who thought every threat could be addressed once it emerges,” said Dr Stephanie Psaki, a former US coordinator for global health security at the White House.

“Those early days and weeks really matter, we need to be prepared before the threat emerges, not react after,” she added.

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