“No safety concerns arose in these studies. With all three vaccination strategies, an immune reaction was observed from day 14 (following vaccination, note) and for at least twelve months,” wrote the international PREVAC study team in Thursday im „New England Journal of Medicine“ published work.
The background: In 2014/2015, the outbreaks of the disease in West Africa gave rise to considerable fears regarding a possible spread to large parts of Africa and also regarding cases that might potentially occur worldwide. Intensive international work was then carried out on the development of prophylactic vaccines.
Three different vaccines
Three such vaccines are now approved in the EU: Ervebo (rVSVDeltaG-ZEBOV-GP, live vaccine for people over 18 years of age) contains a virus called vesicular stomatitis virus that has been weakened and modified to cause a Zaire Ebola virus protein. Vesicular stomatitis virus itself has little or no effect on humans. The vaccine contains only a protein from the Zaire Ebola virus and cannot cause the disease.
The second vaccine is Mvabea (MVA-BN-Filo, recombinant vaccine for people from the age of one). It contains a virus called Vaccinia Ankara Bavarian Nordic that has been engineered to produce four proteins from the Zaire Ebola virus and three other viruses from the same group (Filoviridae). Mvabea contains only parts of the virus and cannot cause Ebola disease.
The third vaccine is Zabdeno (Ad26.ZEBOV-GP, recombinant, also approved for children from the age of one), an adenovirus-like construct is used here, which leads to the formation of a protein from the Ebola pathogen. All three vaccines aim to elicit an immune response through protective antibodies.
Efficacy not easy to test
The problem: The effectiveness of all Ebola vaccines is difficult to test directly. Ebola outbreaks are not that common, strict hygiene measures take effect in such cases – following all, the disease often disappears quickly. Therefore, the scientists determined a certain concentration of antibodies in the blood plasma that is considered effective once morest an Ebola infection (derived from the values in Ebola convalescents).
A total of 2,800 subjects were enrolled in the study in four West African countries, 1,400 adults and 1,401 children (1 to 17 years). The randomly selected study participants received either the third vaccine (Zabdeno) and 56 days later one dose of Mvabea (recombinant vaccine), the first vaccine (Ervebo) and 56 days later a placebo, the third group two doses of Ervebo (distance: 56 days) or a placebo injection each.
Stronger immune response in children
The results support a protective effect in each of the groups. When the two different vaccines were combined, 41 percent of the adults and 78 percent of the children were likely to have protective antibody levels following twelve months. This was also the case for 76 percent of adults and 87 percent of children on the Ervebo vaccine (once vaccine, then placebo). 81 percent of the adults and as many as 93 percent of the children reacted to two doses of this vaccine with particularly strong antibody protection. The placebo injections showed de facto no effect.
“The data from these two studies reinforce the evidence that the Ad26.ZEBOV-MVA-BN-Filo combination and the rVSVDeltaG-ZEBOV-GP vaccine are safe and immunogenic once morest Ebola disease in children and adults. The immune responses were elicited within 14 days of vaccination and persisted for 12 months,” the study said.
In particular, the rapid reaction of the body’s own immune system with protective antibodies within 14 days should offer the chance of getting Ebola outbreaks under control if the vaccine is made available in good time. An Ebola outbreak in Uganda was last reported from the end of September this year. As of December 13, there were 142 confirmed cases there. 55 sick people (39 percent) died.
