Johnson & Johnson‘s potential coronavirus vaccine prevented severe illness in a small group of Syrian golden hamsters, the company announced Thursday.

J&J researchers vaccinated hamsters with a single dose and then exposed the rodents to the virus four week later, the company said.

J&J said the vaccine elicited neutralizing antibodies, which researchers believe are necessary to build immunity to the virus, in hamsters who got the vaccine. Vaccinated hamsters also appeared to lose less weight than unvaccinated hamsters and didn’t experience severe clinical disease, like pneumonia and mortality. The results were published Thursday in the medical journal Nature Medicine.

“This pre-clinical study further validates our confidence in our SARS-CoV-2 vaccine candidate,” J&J’s Chief Scientific Officer Paul Stoffels said in a press release. “With our Phase 3 trials planned to start this month, we remain committed to expanding our manufacturing and distribution capabilities to enable global access to our SARS-CoV-2 vaccine candidate should it prove to be safe and effective in humans.”

The promising results in hamsters do not necessarily mean the vaccine will provide the same level of protection in humans. But J&J researchers noted the findings are important as Covid-19 is known to progress into severe disease in some humans.

J&J is one of several companies working to develop a vaccine for the coronavirus, which continues to rapidly spread across the globe. The company expects to begin a 60,000-person late-stage trial testing its vaccine sometime this month. It would the largest trial testing a coronavirus vaccine yet.

The U.S. Department of Health and Human Services announced on Aug. 5 that it reached a deal with Janssen, J&J’s pharmaceutical subsidiary, worth approximately $1 billion for 100 million doses of its vaccine. The deal gives the federal government the option to order an additional 200 million doses, according to the announcement. 

J&J said it is using the same technologies for its coronavirus vaccine that it used to make its experimental Ebola vaccine, which was provided to people in the Democratic Republic of Congo. It involves combing genetic material from the coronavirus with a modified adenovirus that is known to cause common colds in humans.

Participants in the phase three trial will be randomly selected to receive a dose of the potential vaccine or a placebo, according to details of the trial, which will determine whether the vaccine is safe and effective. They will be followed by researchers for more than two years.

The results Thursday follow data published in July that found the J&J vaccine protected non-human primates in a preclinical study.