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Studies on the Congo epidemic: the Ebola vaccine is apparently highly effective – knowledge



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He has not yet been admitted and has saved countless lives: The rVSV-ZEBOV vaccine appears to be highly effective against the deadly Ebola virus. This is confirmed by new studies for which the researchers analyzed the use of the vaccine in case of outbreaks of the disease in the Democratic Republic of Congo.

The experimental vaccine was used in 2014 at the end of the devastating epidemic of Ebola in West Africa, which killed 11,000 people after demonstrating very good protection in animal experiments. Everyone who had achieved it at that time was spared from Ebola. When the disease broke out again in northwestern Congo last April, WHO decided to use rVSV-ZEBOV again.


At that time, rapid and coordinated intervention made it possible to quickly contain the outbreak. 54 cases became known, 33 people died. As early as July it was declared finished. Researchers led by Chad Wells of the Yale School of Public Health report in the PNAS newspaper that the rapid success in northwestern Congo is largely due to the fact that vaccinations started only two weeks after the outbreak was announced .

Vaccination of the ring as an important factor

Using a proprietary dispersion model, Wells and his colleagues looked at how quickly vaccination affected the risk of infection. For this, the scientists combined the poverty, density and mobility factors of the population and compared the model with a scenario without vaccination campaign.

According to their calculations, vaccination reduced both the geographical area at risk for Ebola infection and the probability of transmission by more than 70%. "If the vaccine was started only one week later, the risk area would have been reduced by only 33% and the overall probability of infection at only 45%," the researchers write.

An important factor was therefore also the procedure, as the vaccine was used: ring vaccination. Health professionals identify the contact persons of people infected with Ebola, as well as the people who came in contact with those contacts. Nearly 3,800 of these primary and secondary contacts (rings around patients, so to speak) were immediately vaccinated in the spring of 2018. None of these people subsequently became infected with Ebola. The researchers concluded that the rapid and coordinated response after the outbreak was essential to contain it.

More than 90,000 vaccines since August 2018

However, this rapid response is not possible in the Congo provinces of North Kivu and Ituri. There, the virus has lasted since August 2018 and is still not under control. According to data from the World Health Organization (WHO), more than 1,400 people have had a fever and 931 died by April 27, 2019. An armed conflict is occurring in the eastern region of the country, and there are frequent attacks on helpers and treatment. Health professionals do not have access to many villages, making it difficult to track diseases and their contacts.

But even if conditions are catastrophic in many places, probably without the vaccine, far more people would have died of Ebola. This is shown in a preliminary report by WHO and the National Research Institute of the Democratic Republic of Congo (PDF format), from August 1, 2018 to March 25, 2019.

Thus, more than 90,000 people were vaccinated against Ebola during this period. To assess the efficacy of the vaccine, the researchers evaluated the number of illnesses in the patient's contact persons and compared them with those of unvaccinated persons at risk. From this, they calculated a very good vaccination efficacy of 97.5%.

Effective protection only after 10 days

It was previously thought that the vaccine needed about ten days to be effective. This was confirmed in the study. Of the 57 people who developed Ebola symptoms within 10 days of vaccination, nine died. In contrast, all 15 vaccinates survived, which occurred at least ten days later, Ebola signs.

In addition, the vaccine increases the likelihood of survival of people already infected. This is particularly important because there is still no approved treatment for Ebola.

Although the researchers recognize that their analysis is only an observational study that can lead to distortions. However, the preliminary evaluation suggests that the vaccine could be as effective as it was assumed after the first studies.

As a consequence of the Ebola outbreak in West Africa in 2013, WHO has ordered studies to test potential vaccine candidates. The most promising vaccine is rVSV-ZEBOV. It is a live vaccine developed in 2003 by researchers from the National Laboratory of Microbiology in Winnipeg, Canada. So he was at the time of the Ebola outbreak in West Africa in his already advanced tests. The most recent data seem to confirm the choice of immunization. Researchers will soon publish their findings in a trade magazine.

To protect them, you have to reach people

Despite this positive news, the reality in Congo is still different. The number of Ebola infections is still at a high level, although it was slightly lower after a record at the end of March. So far, the virus has not yet spread to neighboring countries, but the possibility persists.

In mid-April, WHO announced that the Congo epidemic was not a global health emergency. As a result, MSF called for a "better joint effort" against the epidemic. "We need to radically change the way we approach," said Gwenola Seroux, director of MSF's emergency response to ebola. It is necessary to integrate anti-disease measures into the local health system and to work better together with the local population.

In its latest report on the situation in Congo, WHO also writes that social involvement is necessary to prevent future attacks on helpers and health workers. After all, to protect people with Ebola vaccines, you need to reach them first.

So there's still a lot to do. And yet, the new data gives hope. I hope a single dose of vaccine can be an effective remedy for Ebola epidemics. If someone can locate and track patient contact persons. Because, even if the situation is different: The ring vaccination method was used very successfully before: in the eradication of smallpox.

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