Ebola Vaccine: Ebola Vaccination Shows Promising Results in Clinical Trials In Industry

Ebola Vaccine: Ebola Vaccination Shows Promising Results in Clinical Trials In Industry

The virus is part of the Filoviridae family, which also includes Marburg virus. Ebola was first discovered in 1976 near the Ebola River in the Democratic Republic of Congo. Since then, outbreaks have appeared sporadically usually in forested parts of Central and West Africa. In 2014, the largest and most complex Ebola outbreak in history occurred in West Africa with over 28,000 cases and 11,000 deaths. This outbreak highlighted the need for a safe and effective vaccine against the virus. Researchers had been working on Ebola vaccines for decades but none had reached Phase 3 efficacy trials until recently.

Development of rVSV-ZEBOV Vaccine

In 2003, the Public Health Agency of Canada began collaborating with Merck & Co and other groups to develop a new vaccine platform using vesicular stomatitis virus (VSV) which is genetically engineered to express an Ebola virus protein. Ebola Vaccine This recombinant vaccine, called rVSV-ZEBOV, trains the immune system to recognize the Ebola virus glycoprotein. Early studies in non-human primates found the vaccine fully protected monkeys from challenge with a lethal dose of Ebola virus. In 2015, as the West Africa outbreak was winding down, the vaccine was fast-tracked into the first efficacy trial in humans.

Phase 3 Trial Shows High Efficacy

The Phase 3 trial, named rVSV-ZEBOV-Ebola ça Suffit!, was conducted by an international partnership including WHO, Medecins Sans Frontieres and the governments of Guinea and Sierra Leone. It was a ring vaccination trial design where contacts of Ebola patients and contacts of contacts were vaccinated to establish a buffer of immune individuals around new cases. The double-blind, cluster-randomized trial enrolled over 11,000 people in Guinea between December 2015 and May 2016. Results published in 2019 showed the rVSV-ZEBOV vaccine was highly protective, with 100% efficacy in preventing Ebola virus disease. There were no cases among vaccinated individuals 28 days post-vaccination. This provided the first clear evidence of efficacy for an Ebola vaccination and gave hope that future outbreaks could be quickly controlled.

Continued Monitoring and Use in Outbreaks

Even after the Phase 3 trial completed, researchers continued monitoring vaccinated individuals to understand long-term protection. A study published in 2021 found antibody responses remained stable for at least three years after vaccination. With evidence of both short and long-term protection, rVSV-ZEBOV became the first Ebola vaccine to receive regulatory approval when it was approved by European Medicines Agency and given a positive scientific opinion from the WHO Strategic Advisory Group of Experts (SAGE) on Immunization. This paved the way for its use in subsequent Ebola outbreaks in the Democratic Republic of the Congo and elsewhere in Central Africa. However, questions remain about safety and efficacy in certain populations like children, pregnant women, and immunocompromised individuals. Ongoing studies continue evaluating these factors.

Combination Vaccines Show Promise

While rVSV-ZEBOV provides excellent protection on its own, researchers are continuing to develop other vaccine options that could potentially be used in conjunction for stronger and more broadly protective immunity. Studies have explored Multivalent vaccines that target additional Ebola virus strains like Sudan ebolavirus. A Phase 1 trial published in 2019 found a bivalent vaccine using both Zaire and Sudan strains was immunogenic and well-tolerated. Other investigations have incorporated additional viral proteins or adjuvants to enhance and extend the immune response. A heterologous prime-boost approach using rVSV-ZEBOV followed by an adenovirus type-26 vector expressing Ebola glycoprotein (Ad26.ZEBOV/MVA-BN-Filo) showed promise in non-human primates and is now undergoing clinical evaluation. These multifaceted vaccine strategies could ultimately provide broader, more durable protection against all circulating ebolaviruses.

After decades of research, significant progress has been made towards developing an effective Ebola vaccine. The Phase 3 demonstration of protection by rVSV-ZEBOV established it as the first licensed vaccine against the virus. Continued use in outbreak response since approval has shown its ability to efficiently control transmission when properly implemented. Ongoing studies aim to expand protection for more populations and strains. While challenges remain, the progress so far provides hope that long-term control and possible elimination of Ebola virus disease may one day become a reality through widespread use of safe, effective vaccines.

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