Can the rVSV-ZEBOV vaccine stop the new Ebola outbreak?


ebolaThe rVSV-ZEBOV experimental vaccine proved effective against the Ebola virus in clinical trials with humans but there are doubts about whether it will be able to stop the new outbreak suffered by the Democratic Republic of the Congo.

On May 8, the Democratic Republic of the Congo (DRC) declared a new outbreak of Ebola , and the country’s health authorities published a report on the 20th of the same month in which they indicated that since April 4 a total of 46 cases of infection by this virus, of which 21 had been confirmed, another 21 were considered probable, and four were suspects. As of May 26, there were already 35 confirmed cases, and then the number of deaths.

This is the ninth outbreak of disease that occurs in DRC since it was discovered in 1976, but this time the World Health Organization (WHO) has reacted more quickly and last week has already begun to vaccinate health workers who work in the affected areas, a vaccination that will be extended to people who have come in contact with the infected, with the aim of curbing the spread of the virus outside the Congolese borders.

The vaccine that has begun to be administered is the rVSV-ZEBOV, which lacks a license, but whose efficacy was proven in 2015 in a major trial conducted in Guinea. This drug, which according to the WHO has a one hundred percent effectiveness, contains a porcine virus, which is harmless to humans and used as transport. A part of the virus is eliminated and an Ebola glycoprotein is added. In this way, vaccinated people generate antibodies that prevent the development of the disease.

Will this vaccine against Ebola in Congo be effective?

RVSV-ZEBOV, despite its proven efficacy and safety in clinical trials, is the first time it has been used in DRC during an Ebola outbreak. However, the intense heat and the lack of means play against it, since this vaccine needs to be kept between -60ºC and – 80ºC. Once thawed, it cannot be refrozen, and before administering it should be stabilized, progressively increasing its temperature by degrees, with great care.

Each infected by Ebola can infect other four people, so to prevent an epidemic should be vaccinated 80% of the population

The vaccine, which has already sent more than 7,500 doses to DRC, now has to demonstrate its ability to stop the spread of the disease in the context of an epidemic outbreak like the current one. And for the protective effect of the medication to have the necessary effect it has to be given what is known as group immunity, which is achieved when a percentage of vaccinated population is reached, from which the rest of the community (including those who have not wanted to or have not been vaccinated) is protected, since the number of immunized people constitutes a network that prevents the virus from expanding. According to the estimates of the experts, each infected with Ebola can infect another four people, so if the virus reaches crowded areas to prevent an epidemic, it would be necessary to administer the rVSV-ZEBOV, or another vaccine of similar efficacy, to the 80% of the population.

The keys to eradicating the Ebola outbreak

Volunteers from the non-profit organization Médecins Sans Frontières (MSF), who have extensive experience in the fight against this and other infectious diseases in areas of the planet with limited financial and health resources, emphasize the importance of ring vaccination in which the contacts of the infected are immunized, and the contacts of these contacts -including all the health personnel-, together with close monitoring of all contacts of the sick.

Among the population at risk that should be vaccinated should not only include health professionals, but also all those who handle waste, those in charge of transporting patients, and workers in funeral homes. And although the WHO does not recommend vaccinating either pregnant women or children under six years of age for fear of possible adverse effects of the vaccine not proven in these sectors of the population, from MSF have warned that excluding these people is a greater risk.

In addition, in studies conducted in Guinea, 15 women who were pregnant unknowingly or who became pregnant shortly after receiving the vaccine were vaccinated, and the immunity was equally effective without presenting any serious side effects.

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