The recently developed vaccine, rVSV-ZEBOV, is one of two that have received preliminary testing among humans.
The World Health Organization (WHO) trial, whose results are published in both The Lancet and The BMJ, was designed by researchers from the University of Bern in Switzerland.
A technique known as "ring vaccination" was the inspiration for the trial. This method involves tracking down and vaccinating anyone who may have been exposed to someone carrying a virus, in order to contain its spread. Ring vaccination was behind the eradication of smallpox in the 1970s.
For the trial, researchers first identified people who, within the previous 21 days, had been in close contact with someone that had recently contracted the Ebola virus. These people were considered to be directly at risk and included relatives, household members and clinical staff.
Next, they identified people who might have been indirectly at risk of contracting the virus. These included the neighbors and work colleagues of people identified in the first step of the trial. Together, all of these people were considered to be part of a "ring," and if they were considered eligible to receive the rVSV-ZEBOV vaccine, they were asked to participate in the trial.
A total of 90 rings were identified for examination by the researchers, consisting of 5,415 contacts who were eligible for vaccination. Of these, a total of 3,512 individuals were recruited and received the vaccination.
Participating rings were then randomly assigned into one of two equally sized groups. One group received the Ebola vaccine immediately, while the other group was vaccinated after 21 days - the incubation period of the virus.
Although this approach meant that some participants would likely contract Ebola, study author Dr. Matthias Egger states that it was the only way they could test whether the vaccine really worked.
Could this be the end of the Ebola epidemic in West Africa?
The researchers found that none of the people who were vaccinated immediately contracted Ebola, compared with 16 cases of Ebola reported in the group whose vaccination was delayed. Each of these 16 cases developed within 6 days of the vaccination being administered. After this time, no further cases were reported.
Dr. Sven Trelle, from the Clinical Trials Unit at Bern University Hospital, states that these findings indicate the vaccine offers full protection from Ebola after around 1 week.
- The 2014 Ebola outbreak is the worst outbreak ever recorded
- Ebola has a fatality rate of up to 90%
- The virus is characterized by abrupt onset of fever, weakness and headache.
Looking at the rings overall - which contained several individuals who had not received the vaccination - the researchers observed that a 76% level of protection had been afforded, suggesting that implementing the vaccine had a broadly disruptive effect on virus transmission.
"It is not just the efficacy of the Ebola vaccine that has now been shown but also the effectiveness of the ring vaccination strategy," explains Dr. Egger. "This could finally be the beginning of the end of the Ebola epidemic in West Africa and also be useful when combating this disease in the future."
Following the success of the initial trial, a data and safety monitoring board advised that the trial be expanded to gain further evidence on the vaccine's effectiveness. The board suggested stopping the randomization, however, and simply vaccinating new clusters of eligible participants.
"The continued enrollment, immediate vaccination, and follow-up of clusters will generate additional data about the effectiveness of ring vaccination to protect communities through herd immunity, and will hopefully help to stop Ebola virus disease transmission in Guinea," the authors conclude.
While Guinea has been one of the countries most affected by the Ebola epidemic, a recent report published in The Lancet Infectious Diseases suggests that rising numbers of malaria deaths have greatly exceeded the total number caused by Ebola, possibly due to the manner in which Ebola disrupted the country's health care facilities.