Hantavirus: the disease with no vaccine

Some of the hantaviruses induce relatively mild renal problems, but the mortality rate for others in this category can be as high as around one in seven. The respiratory complications are often more dangerous, with a mortality rate that can reach three out of every five cases of infection. The symptoms, which usually manifest within a few weeks after exposure, are the usual catalogue of unpleasantness: fatigue, stomach pain, nausea and vomiting, diarrhoea, and shortness of breath. 

There are typically thousands of cases of hantavirus infection annually in East Asia, and perhaps a couple of thousand in the European region. The Americas tend to incur fewer – several hundred – but with a higher fatality rate because the New World forms of the virus tend to induce the more dangerous respiratory illnesses. 

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Evidently, you don’t want these viruses to get inside you. The good news is that, unlike, say, coronaviruses, they’re not easily transmitted. The viruses are carried by rodents (which generally don’t themselves suffer symptoms) and are typically caught by humans by breathing air contaminated with rodent urine, droppings, or saliva – or occasionally from contaminated food. 

Some hantaviruses can also be spread through the bites of ticks or mites. It’s not yet clear whether these viruses can be spread directly from person to person – that’s thought generally to be not the case, but the World Health Organisation has said this might have happened on the densely populated cruise ship, on board which no rodents have been found. As we discovered in the early days of Covid, these ships create the perfect conditions for outbreaks of infectious disease.

It’s suspected that the hantavirus was picked during one of the cruise’s stops in South America, perhaps at Ushuaia in Tierra del Fuego – the first fatality happened in the mid-Atlantic after leaving that port. That would lend support to the idea that this strain is the so-called Andes virus, responsible for more than a hundred reported human cases every year, mostly in Argentina and Chile. 

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Two of the passengers who died had been travelling in South America before they boarded the ship at the start of April (it’s best to be especially vigilant when hiking or camping in the Andes).

The Andes strain is one of those that causes respiratory problems and has a fatality rate of around 40%. Rare cases of human-to-human transmission have been reported for it before, but the evidence for that has previously been contested. 

The highest risk of catching this and other hantaviruses tends to occur in rural areas where people may be living in close contact with rodents. Those dangers are made worse where humans have encroached into the natural habitats of wild rodents. It’s another reminder of one of the lessons of Covid: that wild animal populations are awash with viruses that we know little or nothing about, but to which we are increasingly exposing ourselves as human activities expand.

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All the same, there’s no reason to fear that the Dutch ship has seeded a new pandemic. As well as the three deaths, there are currently one confirmed and three suspected cases of infection, and all are being closely monitored. The eighty or so other passengers are being advised to maintain physical distance and to stay in their cabins as much as possible.

There is no general vaccine against hantaviruses. For those infected, all that can be done is to treat the symptoms. A vaccine against an East Asian strain, called Hantaan river virus, does exist and is widely administered in China, where it may have significantly reduced hantavirus-linked fatalities. But it doesn’t seem to work against European or American strains, and there are no approved vaccines in those regions. 

A promising clinical trial was reported in 2024 for a vaccine against both the Asian and European forms, but we’re still a way off cracking this problem globally.