A single dose of highly diluted VSV-Ebola virus (EBOV) vaccine is still protective against the disease, according to investigators at the National Institutes of Health.

Since August 2018, 250,000 people have received the investigational VSV-EBOV vaccine as a part of a “ring vaccination” program. This program is intended to help stem the outbreak.

Researchers analyzed cynomolgus macaques and an updated vaccine component to match the EBOV strain that circulated in West Africa from 2014-2016. The VSV-EBOV vaccine is based on a live-attenuated vesicular stomatitis virus, delivering an EBOV protein to elicit a protective immune response.

Several dosage strengths were tested, including a strength with 10 million plaque-forming units (PFU). Macaques were vaccinated 28 days prior to infecting them with a lethal dose of EBOV. The animals were monitored for 42 days after the initial infection, and macaques given the lowest dose appeared completely protected from the disease due to EBOV.

Scientists concluded that their findings could help make more vaccines available for more people and may reduce adverse reactions to the vaccine, including injection site irritation, headache, fever, and chills.


Candidate ebola vaccine still effective when highly diluted, macaque study finds. NIH website. https://www.nih.gov/news-events/news-releases/candidate-ebola-vaccine-still-effective-when-highly-diluted-macaque-study-finds. Published October 18, 2019. Accessed October 21, 2019.