Ebola vaccine trial team follows-up with a vaccine trial participant, Katongourou, Guinea. Courtesy of WHO/S. Hawkey
The World Health Organization (WHO), partners and affected countries are stepping up planning for how to use an Ebola vaccine in response to an outbreak. The Ebola outbreak that struck Guinea, Liberia, and Sierra Leone in 2014 prompted the search, on an exceptionally accelerated schedule, for a vaccine to prevent the disease. Although there has been more than one promising candidate, the vesicular stomatitis virus-ebola virus (VSV-EBOV) vaccine was selected based on an algorithm produced by the WHO Scientific and Technical Advisory Committee on Ebola Experimental Interventions for the critical Phase III trial in Guinea and Sierra Leone. The committee considered various parameters, including efficacy in non-human primates the ability to provoke an immune response in humans in the early days after vaccination, and availability.
In this article, three experts from WHO, the Sierra Leone Expanded Program on Immunization (EPI) and the Centers for Disease Control and Prevention (CDC) comment on the future of the VSV-EBOV vaccine:
Dr. Marie-Pierre Preziosi, Medical Officer, Initiative for Vaccine Research, WHO
“We can now look ahead and say yes, there will most likely be an Ebola vaccine on the market. The question is when? At present we believe it will take more than one to two years for this to happen. Once a product is licensed we should be prepared to move swiftly and with clear operating procedures and agreement between countries worldwide.
"That’s why WHO convened a Global Ebola Vaccine Implementation Team. This includes partner organizations’ technical experts and representatives from the 3 countries most affected by the West Africa outbreak: Guinea, Liberia and Sierra Leone. We also engaged with countries previously affected by an Ebola outbreak: Democratic Republic of Congo, Sudan and Uganda.
"Initially we envision the vaccine being used as part of the response to an outbreak.
"First, protection of high-risk individuals, primarily health workers and frontline workers. And here, we are not just talking about doctors and nurses. This category includes all staff at a health center, including cleaners and frontline workers involved in burial of the dead.
"Second, we protect specific groups in the general population. We perform what we call ring vaccination to protect the circle of people around someone sick with Ebola.
"This means we vaccinate all people who have been in direct contact with this person and the people who have been in contact with those contacts. In an outbreak that appears to be spreading rapidly we do geographically focused vaccination – meaning we immunize people living in the area surrounding a cluster of cases in an entire village or sub-district. This is similar to the type of immunization campaigns we do when there are cholera outbreaks.”
Dr. Dennis Mark Child Health EPI Manager, Ministry of Health and Sanitation, Sierra Leone
“The vaccine will only be useful for cutting short an outbreak if we identify any cases that occur promptly and then swing into action. Above all, we must stay alert and do superb surveillance.
"It is exciting to have an effective vaccine in the pipeline, but knowledge about Ebola is evolving. Early in Sierra Leone’s outbreak, we believed that the virus remained in semen for no more than 3 months among male survivors of Ebola. Now it appears the virus can stay in the semen for as long as a year. This finding has an impact on how we will use the vaccine to protect the sexual partners of people who recovered from Ebola.
"The vaccines that have been tested tend to make some people feel quite sick for one to two days with fever, aches and fatigue. This could affect acceptability. We already have problems with vaccine hesitancy in our country.
"But something interesting happened during the outbreak. There was 1 local man who volunteered to participate in the trial of the vaccine. Afterwards, his wife was in contact with a person who was sick with Ebola. She did not want to take the vaccine – until he came forward publicly in favor of it. So now we believe that former trial participants can serve as champions for the new vaccine.”
Dr. Jane Seward, Senior Adviser, Sierra Leone Trials to introduce a vaccine against Ebola, CDC
“People should be aware that in an emergency, we could already use this vaccine, under a clinical or research trial protocol and emergency use licensure. This should be reassuring to the public. But we also need to recognize that bringing a vaccine to market usually takes at least seven years. This vaccine is being pushed forward under emergency conditions, but we still have quite a way to go.
"For now, we know that based on preliminary results from the Guinea trial, the VSV-EBOV vaccine is likely to provide good short-term protection. It will be useful to have information about longer-term protection, which will be needed to protect groups at risk, such as healthcare workers, before they are ever exposed to Ebola. Also, there are other vaccines in clinical trials that may complete testing and be licensed for use in the future. That is to be hoped for.”