The latest yellow fever outbreak that swept through Congo and Angola has finally ended, according to the World Health Organization. The outbreak caused 965 confirmed cases of the disease—though thousands were suspected—and killed around 400 people, reports the Associated Press. No new confirmed cases from either country, however, have been reported in six months.

There is no cure or treatment for yellow fever, which is transmitted through the bite of infected Aedes or Haemagogus species mosquitoes. Once a person is infected, doctors can only treat their symptoms, which usually manifest within three to six days. These include fever, headache, vomiting and back pain. Around 15 percent of patients will progress to a more severe stage, which results in multiple organ failure. Up to 50 percent of people who reach this final stage of the disease will die.

The first cases of yellow fever were confirmed in Angola in late 2015, where it spread throughout the country and then moved on to the neighboring Democratic Republic of the Congo.

Yellow fever is easy to vaccinate against. The worldwide vaccine stockpile stands at 6 million doses, but the outbreak in Congo and Angola depleted the available vaccines multiple times. Once the stockpile is depleted, it takes nearly six months to make more. For the most recent outbreak, over 30 million people were vaccinated, according to the WHO.

During this latest outbreak, the WHO approved a radical measure to compensate for the shortages: They began using 20 percent doses on local Angolan and Congolese populations. Less vaccine means a shorter protection period from yellow fever, though the exact timeline is unknown.

The only way to prevent future yellow fever outbreaks is to provide full vaccinations to the populations of the two countries. “Yellow Fever outbreaks like the one in Angola and the DRC could become more frequent in many parts of the world unless coordinated measures are taken to protect people most at risk. Therefore we need to implement a strong preventive approach to vaccinate the population at risk across the region,” WHO’s regional emergency director, Dr. Ibrahima Socé Fall says in a press release.

Earlier this month, Brazil reported a virulent yellow fever outbreak. Doctors have identified 568 cases, mostly in rural areas, reports Jonathan Watts at The Guardian. The local monkey population has also been devastated. Biologists are worried about endangered species of monkey, which could be completely wiped out by this latest outbreak.

As average global temperatures increase, making a more hospitable environment for mosquitos and other disease-carrying insects, we must be more aggressive in our strategies to prevent outbreaks of diseases like yellow fever. Increasing immunization stockpiles and rethinking vaccination strategies are just the first few steps.