Early last week, I wrote that there was a serious outbreak of the hemorrhagic virus Ebola reoccurring in the African nation of Congo.

Officials are now alarmed as Ebola has now been reported in one of Congo’s few urban centers.

Congo has confirmed a case of Ebola in Mbandaka, a city of 1.2 million, marking the first urban case in the latest outbreak, which is now the most serious since the epidemic that raged across West Africa between 2014 and 2016.

Ebola is much harder to contain in urban areas, so this development compounds the risk of contagion. The World Health Organization’s lead response official called the new confirmed case “a game changer.”

“This is a major development in the outbreak,” said Peter Salama, the WHO’s deputy director general of emergency preparedness and response. “We have urban Ebola, which is a very different animal from rural Ebola. The potential for an explosive increase in cases is now there.

In fact, three cases have been reported in that city. A major vaccination campaign with a new vaccine against Ebola is slated to begin next week.

The World Health Organization on Friday decided not to declare the outbreak a global health emergency, but it called the risk of spread within Congo “very high” and warned nine neighboring countries that the risk to them was high. WHO said there should be no international travel or trade restrictions.

The outbreak is a test of a new experimental Ebola vaccine that proved effective in the West Africa outbreak a few years ago. Vaccinations are expected to start early in the week, with more than 4,000 doses already in Congo and more on the way.

Currently the number of potential cases of Ebola to be identified is 44, and the death toll now stands at 23. The level of concern among public health professionals is now such that the U.S. Centers for Disease Control and Prevent (CDC) is preparing to deploy staffers to several cities and towns in the region.

The CDC maintains an office in Kinshasa, the capital of Congo, about 350 miles from the epicenter of the outbreak. The dozen or so staffers who work in that office are likely to deploy to the hot zone once they receive a formal invite from Congo’s health ministry.

In an interview, Pierre Rollin, one of CDC’s top Ebola experts, said the World Health Organization (WHO) is leading the response and coordinating among both governmental and nongovernmental organizations responding to the ongoing outbreak.

“We’re offering them a roster of 12 or 15 people that will be able to go there,” Rollin said. “They’re ready to go as soon as they’ve got an invitation. The invitation is from the Ministry of Health through the WHO.”

Hopefully, this outbreak will be contained before further lives are lost.