Ebola: the geography of its spread mirrors that of poverty but vaccination during the epidemic reduces the risk of contracting the virus by 84%

ROMA – The The geographical distribution of Ebola mainly concerns Central and Western Africa. It can be considered a “geographic map” that perfectly overlaps with the geography of poverty, in Africa, as elsewhere. The epidemic has recorded 28,652 suspected cases, 15,261 laboratory-confirmed cases and 11,325 deaths with a mortality rate of 40%, with peaks of over 60%. Humanitarian interventions are and have been in the three countries most affected by the virus, the Democratic Republic of Congo, Liberia and Sierra Leone, but also in Nigeria and Senegal, where the epidemic has been contained.

The symptoms. Ebola hemorrhagic fever is a very serious disease caused by the Ebola virus and is classified in the category of viral hemorrhagic fevers. Ebola viruses are members of the Filoviridae family and the Ebolvirus genus, of which there are five strains: Bundibugyo ebolavirus, Reston ebolavirus, Sudan ebolavirus, Tai Forrest ebolavirus (which replaces the previous name Côte d’Ivoire) and Zaire (now Democratic Republic of the Congo) ebolavirus, .

It is a zoonosis. The natural vectors of the virus are fruit bats of the Pteropodidae family that live mainly in Africa. Monkeys and some antelopes can serve as intermediate vectors. For humans, infection can occur indirectly by ingesting contaminated fruit, or directly by contact with bats and their excrement. The virus is also transmitted directly through bodily fluids (especially blood, vomit and excrement) of infected and diseased humans or animals, whether alive or dead.

The effectiveness of vaccines. Published on Lancet Infectious Diseasea new study reveals that 10 days after vaccination, the risk of being infected with the Ebola virus is reduced by 84% in vaccinated people compared to those who have not been immunized. The study analyzed data collected during the largest outbreak recorded in the Democratic Republic of Congo (DRC) between 2018 and 2020 in which 3,470 cases and 2,287 deaths were recorded. The survey was conducted by Epicentre, an epidemiological research center in Doctors Without Borders (MSF), in collaboration with the Institut National de Recherche Biomédicale (INRB) and the Ministry of Public Health of the DRC. The study, funded by MSF, focused on the rVSV?G-ZEBOV-GP vaccine, the only vaccine against Ebola recommended by the World Health Organization (WHO) for people at high risk of contracting the virus during an epidemic.

Vaccines uncertainties dispelled. “These results dispel uncertainty about the vaccine’s true efficacy: this is the first published study evaluating the efficacy of the rVSV?G-ZEBOV-GP vaccine outside of a clinical trial. It was conducted during the second largest Ebola outbreak ever recorded,” says Sophie Meakin, MSF epidemiologist.

The vaccination strategy. Administered in a single dose, the vaccine is used for ring vaccination of people at high risk of exposure during outbreaks. This strategy involves vaccinating contacts (people who have had contact with an individual infected with Ebola virus), contacts of contacts, health workers and frontline workers. During the 2018-2020 Ebola outbreak in DRC, vaccination began in August 2018 and over 300,000 people were vaccinated.

The drug offers high protection. The study showed that vaccination with rVSV-ZEBOV provides high protection from Ebola virus disease starting from the 10th day after vaccination. Vaccine effectiveness was estimated by comparing the rates of positive Ebola PCR tests among vaccinated and unvaccinated people. All people had reported contact with an Ebola-infected person and had undergone PCR tests at health facilities to confirm whether or not they were carriers of the disease. In total, 309 people tested positive, 309 had symptoms but tested negative. Vaccination reduced the risk of developing the disease by 84% after 10 days. There were slight variations by sex: the vaccine was 80% effective in women and 86% in men.