The World Health Organization (WHO) declared a new Ebola outbreak in the Democratic Republic of Congo (DRC) a public health emergency of international concern on Sunday.

However WHO Director-General Tedros Adhanom Ghebreyesus stressed in a statement it “does not meet the criteria of pandemic emergency” and advised countries against closing their borders.

The outbreak was first reported in the DRC’s eastern Ituri province on Friday and there are already hundreds of suspected cases, including one that crossed the border into Uganda. The latest strain of the virus has no vaccine either, according to the Africa Centres for Disease Control and Prevention.

Ebola is transmitted through blood and other bodily fluid as well as contaminated surfaces. Symptoms include fever, body pain, weakness, vomiting “and, in some cases, bleeding,” according to the WHO.

Health officials believe the outbreak started in late April, Dr. Jean Kaseya, director general of Africa CDC, said during a Saturday press conference conducted by video call. There are now 336 suspected cases and 87 deaths, he said.

Cases so far have been mostly detected in two mining towns, called Mongwalu and Rwampara, where many people come and go for work. “We are talking about a region that is a very vulnerable and fragile region,” said Kaseya.

On May 14, a 59-year-old Congolese man died from the virus in Kampala, the capital of neighboring Uganda.

In his remarks Saturday, Kaseya outlined how many people the man was likely in contact with before his death, and the importance of using protective equipment.

“Someone came from DRC, landed in Uganda, went to hospital,” he said. “He was sick in this community and he was surrounded by a number of people. He took public transportation to Uganda.” The man died in the hospital but his body was then transported back across the border to the DRC for burial, Kaseya said.

Given its high transmissibility, infectious disease experts recommend that healthcare workers dealing with Ebola patients wear head coverings, as well as goggles, masks or face shields, gloves, gowns and even rubber boots.

Kaseya said he didn’t know what type of protective gear those who had come in contact with the man had used to avoid contracting the virus. “We don’t have manufacturing for PPE,” he said, adding that his team tells him funds are needed and they are working on solving the problem.

It is not yet clear how fast the virus is spreading, officials said. There have been two previous outbreaks of this strain of the virus, called Bundibugyo, but because it is less common than the Zaire strain of Ebola, it is less well understood and there is no known vaccine.

However, researchers say there is now a candidate for an experimental vaccine that they are continuing to study. “We know it was only tested [on] some monkeys,” said Kaseya, who explained it has so far shown an efficacy rate of around 50%, but its potential in human patients has not yet been assessed.

In a statement posted on its website, the African CDC said that it has been working with various health organizations, nonprofits and pharmaceutical companies “to reinforce cross-border surveillance, preparedness and outbreak response efforts.”

Dr. Craig Spencer, a professor at the Brown University of Public Health who had contracted the Zaire strain of the virus in 2014 while working with Doctors Without Borders, wrote on the social media platform X that the outbreak is already large, even though health officials have only recently recognized it. “This means we’re just learning about this outbreak long after its [sic] already been spreading. This makes it harder to find contacts and all the cases.”

Between 2014 and 2016, 28,600 people were infected and 11,325 people died during the largest Ebola outbreak in history, according to the World Health Organization. That started in the West African nation of Guinea then spread to Sierra Leone, Liberia and several other countries outside the region.