Diluted Ebola Vaccine Effective in Animal Model Study

The current Ebola outbreak in the Democratic Republic of the Congo (DRC) has been ongoing for 14 months. One distinct element of the outbreak response has been the availability of the VSV-EBOV vaccine, which has been administered to nearly 250,000 individuals.

Despite this valuable tool, Ebola has continued to spread throughout the African nation that suffers from poor health system infrastructure. However, scientists from the National Institutes of Health (NIH) are hopeful that diluting a dose of the VSV vaccine could be efficacious and stretch vaccine supplies even further.

Findings from their research in an animal model were published in The Lancet’s journal EBioMedicine.

The VSV-EBOV vaccine is based upon a live attenuated vesicular stomatitis virus and delivers an Ebola virus protein to elicit protective immune responses. However, due to the scale of the outbreak in the DRC, there is a concern that vaccine shortages may occur. One method to combat this shortage could be dose adjustments.

Scientists from the NIH’s Rocky Mountain Laboratories conducted a vaccine dosage study among cynomolgus macaques using an updated vaccine component matching the Ebola virus disease strain that circulated through West Africa from 2014-16.

The investigators tested several different strength doses of the vaccines. Methods included vaccinating macaques 28 days prior to infection with a lethal dose of Ebola virus and then monitoring the animals for 42 days. The study team observed that even the macaques that were given the lowest dose of the vaccine appeared to be completely protected from Ebola virus disease.

More specifically, they determined that the lowest dose, a vaccine with approximately one-millionth of what is being used in the vaccine in the DRC, was just as effective as the highest dose tested in the study.

The investigators are hopeful that the findings may help in making vaccines available for more individuals. Additionally, a lower dose vaccine could reduce the occurrence of adverse reactions including injection site irritation, headache, fatigue, fever, and chills, due to a smaller amount of active ingredients. The authors also note that adjusted dosing could ease the overall burden on vaccine production.

According to a press release issued by NIH, the authors say that “although results from preclinical and clinical studies can differ, these promising findings in macaques of complete protection with a lower-dose VSV-EBOV vaccine help support the possibility of similar clinical trials in people.”

As of October 16, 2019, a total of 3144 cases of Ebola have been confirmed in the DRC with 2044 confirmed deaths. Thus far the rVSV-ZEBOV vaccine, manufactured by Merck, has been the only vaccine used in the outbreak response; however, health authorities have stated that the Johnson & Johnson Ebola vaccine, which requires 2 injections 8 weeks apart, will be introduced into the outbreak response in November.

For the most recent case counts in the Ebola outbreak in the DRC, check out the Contagion® Outbreak Monitor.