No Vaccine for Deadly Hantavirus: Implications for Future Outbreaks

An outbreak of hantavirus onboard the cruise ship MV Hondius has brought into sharp focus the severe challenges posed by this rare but often deadly infection, particularly the lack of specific treatments and preventive vaccines. Three individuals from the ship have tested positive for the virus, including one passenger who tragically died. Among another five people with suspected infections, two have also succumbed. The World Health Organization's director-general, Tedros Adhanom Ghebreyesus, confirmed that the passengers were infected with the Andes virus strain, a variant for which no specific treatments or vaccines currently exist. Scientists suspect some travelers might have contracted the infection in Argentina before boarding the cruise. Hantavirus typically spreads through airborne particles from rodent urine, droppings, or saliva. However, certain strains, like the Andes virus responsible for this outbreak and an ongoing one in Argentina, can occasionally spread between people in close contact. While hantavirus infections are uncommon, some strains exhibit an alarming fatality rate of up to 50%. For over three decades, virologist Jay Hooper at the US Army Medical Research Institute of Infectious Diseases in Frederick, Maryland, has been at the forefront of efforts to develop a vaccine against several hantavirus strains affecting humans, including the elusive Andes virus. Hooper's team has been working on hantavirus vaccines since the 1980s, intensifying efforts in the 1990s with the emergence of new hantaviruses causing hantavirus pulmonary syndrome (HPS), such as the Sin Nombre virus in the US and the Andes virus in South America. A significant breakthrough for his team involved developing realistic hamster models of a lethal disease similar to human HPS, providing a crucial platform for testing vaccine and therapeutic candidates. They have successfully conducted Phase 1 clinical trials for vaccines targeting the Andes virus and two other strains, Hantaan and Puumala. The Andes DNA vaccine has shown promising results in humans, inducing neutralizing antibodies vital for protection. However, its efficacy currently requires a complex regimen of at least three doses (prime plus two boosts), rather than a simpler single-shot or prime-boost approach. A major hurdle for licensing this vaccine lies in the rarity and geographical dispersion of human Andes virus cases, which makes it impractical to conduct a classic Phase 3 efficacy trial. Consequently, researchers are exploring "more creative approaches," emphasizing the role of neutralizing antibodies as a correlate of protection. Beyond the scientific complexities, a significant barrier to the advanced development and widespread availability of hantavirus vaccines is the consistent lack of funding. Hooper also highlights the inherent unpredictability of zoonotic viruses – those transmitted from animals to humans – drawing parallels with the monkeypox outbreak. He suggests that climate change could potentially alter rodent populations, increasing human exposure to these viruses and, consequently, the number of cases. The US military has a long-standing interest in these vaccines due to the risk hantaviruses pose to troops deployed in affected regions.