Merck’s Ebola vaccine has 'major impact,' but U.S. should help as outbreak worsens: experts

Merck's Ebola vaccine has been used in over 40,000 people in the latest outbreak. (WHO)

Merck & Co.’s experimental Ebola vaccine rVSV-ZEBOV has been deployed widely in the Democratic Republic of Congo. But experts are calling on the U.S. government to send CDC specialists to help contain what’s known as the second-largest Ebola outbreak before it becomes a major epidemic.

Since the latest outbreak was declared in August, more than 40,000 people have received rVSV-ZEBOV, the most advanced Ebola vaccine in development, and as the disease continues to spread, more countries could begin vaccination soon, according to the Associated Press. That's up from the 27,000 recipients quoted by the World Health Organization a month ago.

As in previous outbreaks, the vaccine is given under an expanded-access protocol to those who've been in contact with affected people to provide a "ring" of vaccinations designed to prevent further spread.

The Merck shot is having “a major impact,” said Peter Salama, who heads the WHO’s Ebola response, as quoted by Science. A Merck spokeswoman told FiercePharma that the company is manufacturing additional vaccines to maintain a stockpile of more than 300,000 doses for emergency use.

But the disease is still popping up in people who had no known links to existing cases. This outbreak is now the second-largest in history, surpassed only by a devastating surge in West Africa from 2014 to 2016.

RELATED: With outbreak spreading, WHO worries Merck's Ebola shot may run scarce

As of Dec. 9, the number of confirmed and probable cases has reached 498, with 285 confirmed deaths. The new outbreak has lasted longer than previous ones and is showing no sign of easing up. To make it worse, malaria cases are creeping up in the same region.

Several countries neighboring the DRC, such as South Sudan, are facing potential cross-border spread. And front-line responders from the DRC, WHO and NGOs such as Doctors Without Borders are “frankly exhausted” from working around the clock in a conflict zone where armed rebel groups are present.

Extra help is needed, Salama said. Experts are already calling for additional U.S. support to help contain the situation before it spins out of control; CDC specialists were recently pulled from the front line because of U.S. security concerns.

RELATED: Merck’s Ebola vaccine to be used in latest Congo outbreak, with a new hurdle ahead

In a recent New England Journal of Medicine editorial, two Johns Hopkins University researchers pleaded with the U.S. government to “allow CDC staff to return to the field for as long as the WHO and others deem necessary,” given the “highly dynamic nature” of the current outbreak.

Meanwhile, in a JAMA commentary, experts wrote that, “it is in U.S. national interests to control outbreaks before they escalate into a crisis." The article suggested U.S. security and diplomatic resources also be mobilized to work with the United Nations to improve health worker security.

But WHO Director-General Tedros Adhanom Ghebreyesus told reporters last week that the international health agency has the situation under control and praised commitment from the U.S. government.

“They promise to continue supporting us in finance and other (ways), and that, I think, would suffice,” he recently told reporters at WHO headquarters, as quoted by AP. “We can mobilize from other parts, from those institutions who don’t have very strict security provisions like that.”