May 3, 2019 - Health

Ebola vaccine's effectiveness is imperiled by DRC's unrest

Data: DRC Ministry of Health; Chart: Andrew Witherspoon, Harry Stevens/Axios
Data: DRC Ministry of Health; Chart: Andrew Witherspoon, Harry Stevens/Axios

The Ebola vaccine — which appears to have an effectiveness of more than 97% when given 10 days before infection — also must be given quickly once an outbreak starts, according to scientists in a study out this week.

Why it matters: One of the few bright spots about this deadly outbreak in the Democratic Republic of the Congo is the preliminary finding that the rVSV-ZEBOV vaccine is very effective. But the violent disruptions of the hard efforts of public health officials there — causing the WHO chief to warn, "The world has never seen anything like this" — are endangering that benefit.

What they did: The research team from the University of Florida used a spatial model examining human mobility, poverty and population density to see how this impacted the effectiveness of the vaccination program during the prior Ebola outbreak in the DRC in 2018.

  • "Our primary purpose was to investigate the timing and pattern of geographical spread of an Ebola outbreak starting from initial cases," study author Burton Singer tells Axios.
  • They used Merck's rVSV-ZEBOV vaccine, as it was the most effective known vaccine and it was available for distribution, Singer says.
  • The outbreak in May 2018 was in a different location than the current outbreak.

What they found: The vaccination program lessened both the geographical area that was at risk and the risk level for infection within that region, the study found.

  • The vaccination program contracted the geographical area at risk for Ebola by up to 70%.
  • The program reduced the level of risk within that region by up to 70%.

Yes, but: It also shows there may be a significant drop in its ability to lower infection rates in an area if it's given even a week after the infection has started. A delay of a week led to the above effects to drop to 33% and 45%, respectively, the authors say.

  • "I was surprised by the dramatic potential impact across a substantial geographical area of a delay of even one week in initiating vaccinations following an outbreak. Vaccinating people as early as possible is critically important," Singer says.

What's happening now: Unfortunately, the vaccination regime is being stymied in the current outbreak by community distrust and violent attacks, including the recent death of a WHO epidemiologist Richard Mouzoko.

"I’m profoundly worried, because the number of cases increases with the frequency of attacks. They are almost every day. It disrupts our operations, and when operations are disrupted, the virus gets a free ride."
"After Richard was killed, we were operating at very low levels for three days. And if we can’t find cases as soon as possible, and if we aren’t able to vaccinate everyone, there is a build-up of the chances of this spreading to other provinces and neighbouring countries. That chance gets higher and higher."
— WHO chief Tedros Adhanom Ghebreyesus, in Q&A published in Nature

By the numbers: DRC says they've vaccinated 109,844 people since they began vaccinating people on Aug. 8.

  • The only vaccine used so far in this epidemic is Merck's rVSV-ZEBOV vaccine.
  • Beth-Ann Coller, executive director of project management and leadership at Merck, tells Axios the company was glad the preliminary data shows a "robust response" to the vaccine, of which the company had agreed to stockpile 300,000 doses as a donation to the WHO.
  • Because it takes roughly one year to produce these vaccines, Coller says, they are already working to replenish their stocks.
  • Merck is moving to have the vaccine licensed in the U.S. and the EU, she adds.
  • WHO spokesperson Tarik Jasarevic says WHO also has used the vaccine for nearly 5,000 health and frontline workers in Uganda, 1,400 in South Sudan, and just started vaccinations in the town of Gisenyi, Rwanda.

Meanwhile, Ghebreyesus called for more funding from the international community, saying, "We have just 50% of what we need."

  • The Paul G. Allen Family Foundation announced yesterday roughly $2.4 million via its Ebola Response Accelerator Challenge to 3 winners, including the WHO, to focus on the community engagement needed to help make the region safer for treatment and vaccination regimes for this Ebola outbreak.

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