US-based pharmaceutical company Moderna confirmed that it has been working on the development of hantavirus vaccines in collaboration with the Vaccine Innovation Center of Korea University College of Medicine (VIC-K). This comes after an outbreak of hantavirus occurred on a Dutch cruise ship that sailed from Argentina and disembarked its passengers and crew in the Canary Islands on May 10. At least three people aboard the MV Hondius died, and several cases were reported as serious.

Moderna is the Cambridge, Massachusetts-based biotechnology company that perfected messenger RNA (mRNA) vaccines during the Covid-19 pandemic. Following the announcement that Moderna was developing a hantavirus vaccine using this same technology, the drugmaker's stock rose from $49 on May 7 to $55 the next day. But it is important to note that Moderna did not begin work on immunization in the wake of the outbreak at MV Hondius. In fact, the drugmaker undertook this collaborative project with VIC-K in 2023.

The Fight for a Vaccine

The hantavirus outbreak on the high seas has been one of the big international events of recent weeks, which means that many people around the world have only just learned of the existence of this virus—but it is not a newcomer. In fact, hantavirus has been a known pathogen for decades. Transmitted mainly through exposure to the droppings, urine, or saliva of infected rodents, it can cause hemorrhagic fever with renal syndrome (prevalent in Asia or Europe) or hantavirus pulmonary syndrome (more common in the Americas). The wife of actor Gene Hackman may be one of the best known recent people to have died from the latter disease, but it is far from being an exceptional phenomenon. Overall, hantaviruses cause around 50,000 serious and often fatal infections worldwide each year. The so-called New World hantaviruses, such as Andean hantavirus (ANDV), are mostly found in South America and can reach a case fatality rate of up to 40 percent; ANDV is the only hantavirus with documented human-to-human transmission, and just the variant that the World Health Organization identified in MV Hondius.

There is currently no vaccine to prevent ANDV infection, and the Spanish Society of Immunology emphasizes that “there is no licensed hantavirus vaccine in Europe, the United States, or Latin America.” Treatment strategies are oriented to the viral life cycle, host immunological factors, or clinical management of symptoms.

South Korea is the partial exception to this picture. The country reports 300 to 400 cases annually, mainly among young men in their 20s and 30s, and the country's health authorities have included the pathogen on their list of nine priority threats for future pandemic preparedness. A previous-generation inactivated vaccine called Hantavax exists in Korea, but its limited efficacy and production methodology—it's derived from animal brain tissue—keep it far from modern standards.

South Korea was the starting point for Moderna’s most advanced collaboration in this field. The biotech firm and VIC-K signed a research and development agreement in September 2023 under the US company's mRNA Access initiative, a program that provides preclinical-stage mRNA vaccine candidates to academic teams working on emerging or neglected infectious diseases.

The mechanism of the collaboration works like this: The Korean team provides the hantavirus antigenic sequence information and Moderna supplies the corresponding mRNA material. Preliminary results of this early stage research are already available. In February 2025, Park Man-sung's team from the Department of Microbiology confirmed that experimental doses prevented hantavirus infection in mice.

A Vaccine That Could Take Years to Arrive

The distance between a mouse trial and a licensed vaccine for humans is considerable, especially when there is no longer the sense of urgency of the pandemic or the government support of Operation Warp Speed. The vaccine candidate is still in the preclinical phase, meaning it has not begun human trials and faces major funding and regulatory hurdles before that can happen.

In addition, hantaviruses are diverse and have regional variations. Designing a vaccine capable of protecting against multiple strains represents a complex task. Precisely for this reason, this international collaboration seeks to develop a broad-spectrum immunization, effective against more variants than existing vaccines in Asia.

The messenger RNA platform, which during the Covid-19 pandemic demonstrated its ability to produce effective vaccines in record time, offers particular advantages over conventional methods of vaccine development: It can adapt quickly to new variants of a virus, does not require live pathogen culture in the laboratory, and is the easiest to scale up industrially

These data, added to the outbreak in the Hondius, boosted the company's shares by almost 20 percent overnight, something that analysts attributed more to the validation of the technological platform than to immediate commercial expectations—especially in a US political context that has become less favorable to mass vaccination campaigns.

For now, the WHO ruled out that the Hondius outbreak represents the beginning of an epidemic, and stressed that human-to-human transmission occurs only with very close contact. But the episode reminds us of a lesson from the Covid-19 pandemic: The best time to develop a vaccine against a dangerous virus is before that virus becomes a global emergency.

It is noteworthy that Moderna is also developing mRNA vaccines against avian influenza, noroviruses, and other pathogens considered priorities for pandemic preparedness. With respect to hantavirus, other agencies are working on vaccine development, most notably the long-standing work of the US Army Medical Research Institute of Infectious Diseases.

This story first appeared on WIRED en Español and has been translated from Spanish.