Ebola vaccines could be given as an emergency intervention to individuals exposed to the virus.
Since 2013, the world has seen 2 major Ebola virus disease (EVD) outbreaks that have shaken public health and health care to its core. In the face of these devastating epidemics though, several vaccines were developed and deployed to reduce the transmission of the blood-borne disease.
The ongoing outbreak in the Democratic Republic of the Congo (DRC) has been particularly brutal. According to the World Health Organization, there have been 3313 cases of Ebola resulting in 2203 deaths. The outbreak was declared in August of 2018 and just as we saw during the West African Ebola outbreak from 2013-16, health care-associated transmission is a key trend.
Fortunately, the development of new vaccines have given response efforts a new tool, both in terms of pre- and post-exposure prevention. One of the vaccines rVSV-ZEBOV, a recombinant vesicular stomatitis virus-Zaire Ebola virus vaccine, had a trial run in 2015 when it was still unlicensed. Developed by Canadian scientists and licensed to Merck in 2014, the vaccine has been deployed for the most recent outbreak and has shown 97.5% efficacy during utilization in a large-scale ring vaccination effort.
Prior to the large-scale deployment though, it was used for an exposure in 2015 involving 65 people who had direct contact with a health care worker who presented with a viral reactivation (i.e. previously infected, the health care worker recovered and experienced a reactivation of the virus and even reinfection) in the United Kingdom.
Investigators reviewed the use of rVSV-ZEBOV for those 45 exposed individuals who were determined to have a significant exposure that would warrant high risk for disease transmission. Of those, 26 received the vaccine between October 10-11, 2015 and following 14 days, 39% had seroconverted. Twenty-eight days after vaccination, 87% had seroconverted, and by 3 months, all of those vaccinated had. Researchers found that neutralizing antibody responses were detected on day 14 within 36% and then 72% at a full year.
There were no severe vaccine-related adverse events reported and no exposed person became infected with Ebola virus disease. Of those with mild side effects, the most common were fatigue, myalgia, headache, and fever. Interestingly, many recipients did develop a fever that triggered screening as there was concern that they were in fact developing Ebola virus disease, but fortunately this was just a side effect of the vaccine.
The real-world deployment of an experimental vaccine following high-risk exposures is extremely important for the current epidemic, but also researchers and future outbreaks. Health care workers are at extremely high risk of transmission when caring for patients with Ebola virus disease and the World Health Organization found that they are between 21 and 32 times more likely to become infected than the general public.
Providing an effective, post-exposure vaccine is beneficial in many ways. It encourages health care workers to continue their critical work with less fear, it ensures that those who survived the virus have options to protect their loved ones (and anyone exposed) should a reactivation occur, and we can safely provide post-exposure prophylaxis for people during such unexpected exposures.
Since the virus persists in body fluids, illness can wholly be reactivated and reinfection can occur as a result of lowering immunity, vaccine intervention is highly important to support public health and health care efforts as we try to reduce survivor stigma.