Research findings by a team of scientists at the University of Texas Medical Branch (UTMB), US, were recently published in The Lancet. The team reported that the experimental mRNA vaccine generated a strong protective response against the Andes virus, one of the few Hantaviruses capable of human-to-human transmission.

In the new study, the UTMB team tested an mRNA vaccine with a mechanism similar to Covid-19 vaccines. The vaccine carries genetic instructions that help body cells create two harmless surface proteins of the virus. This teaches the immune system to recognize and fight off the actual virus.

Scientists administered one dose of the vaccine to 30 hamsters. Four weeks later, they were exposed to a lethal dose of the Andes virus. The hamster model was used because it can closely mimic the severe pulmonary disease this virus causes in humans.

Results showed that all vaccinated animals were completely protected from the disease. At the end of the study, the team found no replicating virus in the examined tissues. In the unvaccinated group, four of five hamsters did not survive beyond day 9 post-exposure.

The vaccine also induced antibody production within 14 days, a crucial factor during rapidly spreading outbreaks. The research team also tested three dose levels: 25 mcg, 5 mcg, and 1 mcg. Protective efficacy was still observed at the lowest dose, although only four of five animals produced measurable antibodies.

The potential for using lower doses has practical implications. During an outbreak, initial vaccine supplies are often limited. If each vaccine dose can be divided while still providing protection, the number of people who can be vaccinated in at-risk areas could increase.

A research illustration of the vaccine. Photo: Vecteezy

One aspect of interest to the research team is the potential for post-exposure vaccination. Andes virus disease has a median incubation period of approximately 18 days in humans. If the vaccine activates immunity within two weeks, there could theoretically be a window for intervention after a person has been exposed to the pathogen but before symptoms appear.

According to doctor Alexander Bukreyev, head of UTMB's vaccine development and viral pathogenesis laboratory, if administered early to high-risk contacts during an outbreak, the vaccine could help the immune system respond in time, limiting viral replication and reducing the risk of developing the disease or further transmission. However, the team stressed that this is currently a hypothesis, not a proven indication.

Experts also noted that the research is still in the preclinical stage. The results have only been observed in animals and have not yet demonstrated efficacy and safety in humans. Additionally, the team only measured viral load in the liver, although in this model, liver indicators typically correlate with those in the lungs.

The next step is human clinical trials. With support from the National Institutes of Health (NIH), US, the UTMB team stated they are accelerating the process of bringing the one-dose vaccine to trials, aiming to better prepare for the risk of dangerous Hantavirus strain outbreaks.

Hantavirus is typically transmitted to humans through contact with the feces, urine, or saliva of infected rodents. The Andes virus, specifically, can spread through close contact with respiratory secretions from an infected person, such as during coughing. This characteristic makes outbreaks more difficult to control.

This virus previously caused an outbreak in Epuyen, Argentina, during 2018-2019. At that time, the transmission chain originated from a social gathering, leading to four waves of infection, with 34 confirmed cases and 11 deaths.

In May, an outbreak on the Dutch cruise ship MV Hondius, departing from Argentina, further highlighted this risk. To date, that event recorded 13 cases and three deaths. Nearly 150 passengers subsequently returned to 23 countries during an incubation period that can last up to 42 days, complicating contact tracing and isolation efforts.

Currently, inactivated vaccines for some Hantaviruses have been used in China and South Korea for many years. However, no vaccine has been licensed in the Americas or Europe for the Andes virus. There are also no approved specific treatments for this disease.

Van Ha (According to The Lancet/UTMB)