The second worst Ebola outbreak ever is currently rife in the Democratic Republic of Congo (DRC). As of April 16, the World Health Organization (WHO) reports a total of 1,290 cases and 833 deaths.

But the WHO also has some good news at this trying time – an experimental Ebola vaccine given to those at risk is 97.5 percent effective, meaning that it’s likely saved thousands of lives.

The WHO recently released a preliminary analysis of data from between May 1, 2018, and March 25, 2019, describing the effectiveness of the vaccine, which is called the rVSV-ZEBOV-GP Ebola vaccine. They are working on a more comprehensive report that will be published in a peer-reviewed journal at a later date.

So far, the vaccine has been administered using a ring vaccination strategy. This means that it’s only being given to those most likely to get infected, such as health workers and those living in affected villages. The vaccine has been given to more than 90,000 people, including nearly 29,000 health care and front line workers.

Out of the 93,965 people who were vaccinated, only 71 Ebola cases occurred. Meanwhile, 880 unvaccinated people became infected in the same time period. The vaccine also seems to work well at preventing the disease in people indirectly exposed i.e. those who have come into contact with someone who has been exposed to the virus. Out of 68,279 vaccinated “contacts of contacts”, only two developed the disease. This led the researchers to conclude that while not perfect, the vaccine has an efficacy of 97.5 percent. This is great news for both the current and future outbreaks.

“Combining this level of collaboration with the ring vaccination strategy and the rVSV-ZEBOV-GP vaccine should contribute to bringing the current Ebola outbreak in the DRC to an end, and to controlling future outbreaks as effectively and rapidly as possible,” the authors write.

They also note that the vaccine has a “high vaccine efficacy against death”. Those who caught Ebola 10 or more days after being vaccinated all survived, but nine out of 56 people who became infected 0-9 days after receiving the vaccine died. However, it takes about 10 days post-vaccination to become fully protected.

“The overall case fatality rate was reduced among all vaccinees who developed Ebola,” the researchers write.

However, the Ebola virus is still on the rise in certain areas. The outbreak has been contained to two provinces in the DRC – North Kivu and Ituri in the east of the country. This means there’s a risk that the outbreak could make its way across the border to Rwanda, Uganda, and South Sudan. Despite this, the WHO announced Friday that they are not declaring the situation to be a Public Health Emergency of International Concern as the disease is currently contained.

While the experimental vaccine is certainly having a positive effect, more needs to be done to minimize the disease’s spread and halt the outbreak, which was first declared on August 1, 2018. A recent study found that many people in the DRC deny the existence of the outbreak or refuse to trust doctors and officials. Changing these attitudes will contribute to the containment of the disease and help bring this devastating outbreak to an end.