New ‘100% effective’ Ebola vaccine

100% effective

The rVSV-ZEBOV vaccine looked so safe and effective during an interim analysis that the team had to stop the delayed vaccination and vaccinate everybody they could, including even children. The further analysis in this study supports those initial conclusions. They found no cases of the disease in the immediately treated group compared to 23 cases in 11 clusters in the delayed or never vaccinated group.

When they zoomed in on each cluster, they could even see that vaccinating individuals in a cluster would stop unvaccinated people in the same cluster getting infected. This suggested they had developed what’s known as herd immunity, where enough people in a group are immune to prevent an outbreak – protecting even those who aren’t vaccinated. Because of this success, it looks like the trial probably helped bring the outbreak in Guinea to an end.

While the data suggests the vaccine is 100% effective, this is not likely to be the definitive number. Biology simply does not work like that. This is especially true when the numbers looked at are so small (23 cases in the control group). The potential inaccuracy of this number likely reflects the challenges in conducting a vaccine trial such as this, for a disease like EVD in the middle of a very serious outbreak.

There is also the fact that no vaccine is perfect. Even one of our very best vaccines, the measles vaccine, is only about 95% effective. Previous studies have even shown that rVSV-ZEBOV produces an immune response in only 94% of individuals. Being certain about the effectiveness is important because computer models suggest that ring vaccination for Ebola may only be successful when there aren’t that many cases.

Despite being carried out under some of the most challenging conditions, the trial reported here appears to be an exceptionally well-run study, comprehensive in its nature and with a very positive result. This surely cements this vaccine as one important tool in controlling outbreaks of Ebola in the future. It also gives us a way to test new vaccines for other viruses that can crop up and take us by surprise, such as Lassa fever virus and Nipah viruses. We just have to hope that scientists have got more vaccines in the pipeline for us to test.

****

Connor Bamford, Post-doctoral Research Assistant, University of GlasgowThe Conversation