The world finally has an Ebola vaccine. On 11 November, European regulators approved a vaccine that has already helped to control deadly outbreaks of the virus — the first time any immunization against Ebola has passed this hurdle.

The decision by the European Medicines Agency (EMA) to allow US pharmaceutical company Merck to market its vaccine means that the product can now be stockpiled and, potentially, distributed more widely, in particular in Africa. In 2015, Gavi, the Vaccine Alliance — a global health partnership that funds vaccine supplies in low-income countries — told Ebola-vaccine manufacturers that it would commit to purchasing vaccines once they had been approved by a “stringent health authority” such as the EMA.

Although several other vaccines against Ebola — a haemorrhagic fever that causes severe diarrhoea, vomiting and bleeding — are in development, Merck’s is the only one that has been tested during an outbreak, where it was shown to be highly effective in preventing infection .

The vaccine, first patented in 2003, has been administered on an emergency basis to quell the ongoing outbreak in the Democratic Republic of the Congo (DRC), which has killed some 2,000 people since it started last year. It was also used during a 2018 outbreak in that country, and in Guinea in 2015. In the current DRC outbreak, hundreds of thousands of people have received the Merck shot, including more than 60,000 health-care workers in DRC and several neighbouring countries.

“This is a vaccine with huge potential,” said Seth Berkley , chief executive of Gavi in Geneva, Switzerland, in a press release after the EMA decision. “It has already been used to protect more than 250,000 people in the DRC and could well make major Ebola outbreaks a thing of the past.” The organization has supported the stockpiling and delivery of Ebola vaccines and hopes to build up a global supply that could be rolled out quickly during future outbreaks of the virus.

The EMA’s approval “makes a big difference”, says David Heymann , an epidemiologist at the London School of Hygiene and Tropical Medicine. But he stresses that research into the Merck vaccine and development of further Ebola vaccines must continue. “The message is that the research is not done. It must continue,” he adds. “It’s really important to continue to study vaccines and develop those second- and third-generation vaccines.” These could offer longer-lasting immunity, target more than one species of Ebola and be easier to store.

Future protection

Merck’s vaccine, which is marketed under the name Ervebo and known to researchers as rVSV-ZEBOV-GP, was tested in a clinical trial conducted in Guinea towards the end of the 2014–16 Ebola outbreak in West Africa. There, the vaccine was administered to people who had been in contact with someone who was infected with Ebola, or with their subsequent contacts. It was found to offer a high level of protection against infection .

Health workers have used this strategy — known as ring vaccination — in the two other outbreaks in which rVSV-ZEBOV-GP has been deployed. But Heymann says it’s important to determine whether the Merck vaccine could be used in other ways — for instance, administered preventively to emergency health workers who might encounter Ebola in the distant future. This would mean determining how long the vaccine’s protection lasts, and whether an additional dose — a booster — can extend immunity.

Such studies are in the works with rVSV-ZEBOV-GPand competing vaccines, says Adrian Hill, a vaccinologist at the University of Oxford, UK. “The question remains, which vaccine would you give to, say, health-care workers to prevent them getting Ebola?”

Merck’s product protects against the Zaire species of the Ebola virus, which is behind the current DRC outbreak and the 2014–16 West Africa outbreak. It will be important to develop vaccines against other species of the virus — especially the Sudan species, which has caused seven known outbreaks since 1976, says Hill, who helped test an Ebola vaccine that was shelved by the London-based pharmaceutical company GSK in August.

There are seven other Ebola vaccines in various stages of clinical testing, according to the World Health Organization (WHO) in Geneva. In September 2019, the WHO announced that a vaccine manufactured by Johnson & Johnson in New Brunswick, New Jersey, would be used in the current DRC outbreak. Last week, the company submitted that vaccine for EMA approval.

Unlike the Merck vaccine, which is given in one dose, the Johnson & Johnson immunization requires a booster shot administered 56 days after the first injection. In the DRC, it will be given to populations at risk of Ebola, such as health-care workers, in areas where the virus is not already circulating.

And next month, Gavi’s board will decide whether to establish a global stockpile of Ebola vaccine. Merck, which is headquartered in Kenilworth, New Jersey, is also seeking approval of the vaccine by the US Food and Drug Administration.