Ebola vaccines trigger durable responses in African adults and children

Largest study to date confirms Ebola vaccine safety, with immunity lasting up to a year.

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Health workers at the National forum for ebola eradication in DRC. Credit: Gavi/2019/Frederique Tissandier
 

 

Two existing Ebola vaccines trigger durable immune responses, with antibodies still detectable a year after adults and children received their first doses, one of the largest Ebola vaccination trials to date suggests.

The study, published in The New England Journal of Medicine, also confirmed the safety of three different regimens of Merck, Sharpe and Dohme’s Ervebo (rVSV-ZEBOV) vaccine, and Johnson & Johnson’s Zabdeno (Ad26.ZEBOV) and Mvabea (MVA-BN-Filo) vaccines.

"The data collected during this clinical trial are valuable because they help confirm the safety and potential efficacy of the available vaccines."

Necessary data

Although these vaccines are already licensed, and have been used in previous Ebola outbreaks involving the Zaire strain of the virus, this new data will aid efforts to establish how best to use these vaccines in different population groups.

"The data collected during this clinical trial are valuable because they help confirm the safety and potential efficacy of the available vaccines, making it possible to refine the vaccination recommendations during both Zaire ebolavirus epidemic and inter-epidemic periods, in populations at risk," said the trial’s principal investigator, Prof Yazdan Yazdanpanah of Paris Diderot University in France.

Zaire strain

Ebola epidemics periodically occur in various sub-Saharan African countries, with the Zaire ebolavirus species accounting for more outbreaks and human cases than any other strain - including the 2014–2016 West Africa outbreak and the 2018–2020 outbreak in the Democratic Republic of the Congo.

The Ervebo vaccine was originally designed as a one-dose vaccine, and is currently recommended for reactive ring vaccination during outbreaks. This means vaccinating anyone who is likely to have come into contact with an individual who contracts Ebola, rather than vaccinating entire populations.

The Zabdeno and Mvabea vaccines were designed to be used in combination, with a dose of Zabdeno administered first, followed by a dose of Mvabea 56 days later. Because of the delay between the recommended doses, this regimen is currently recommended for people who are at moderate risk of Ebola but are not considered to be at high risk.

Durable responses

The new study, which involved 1,400 adults and 1,401 children aged 1 to 17, was designed to measure the rapidity, intensity and durability of immune responses generated by three different vaccine regimens: One dose of Zabdeno, followed 56 days later by a dose of the Mvabea vaccine; a single dose of the Ervebo vaccine; or one dose of Ervebo, followed 56 days later by a booster dose of the same vaccine.

It was carried out by the Partnership for Research on Ebola Vaccinations (PREVAC) consortium, which mobilised African, European and US research teams working together in Liberia, Guinea, Sierra Leone, and Mali.

The study suggested that all three regimens are safe and well-tolerated in adults and children, with the most common side effects being injection site pain, fever, muscle and joint pain, and headache, in the 7 days after receiving the first, second or booster doses.

Each of the regimens generated a rapid increase in antibodies against the virus after approximately 14 days, peaking at between 1 and 3 months after the first dose. Although the researchers were unable to assess protection from disease, because there were no incident cases of Ebola during the trial, current scientific literature suggests a strong correlation between the amount of these antibodies and the level of protection against the virus. Antibodies were detected up to 12 months after the first injection, and children had higher immune responses than adults.

Booster dose

Until now, data on booster vaccinations with the Ervebo vaccine have been limited. This trial suggested that a second dose at 56 days provided a temporary boost in antibody concentrations, but that this was relatively short-lived. Even so, the new data on a 2nd booster dose of Ervebo are exciting because they suggest a second dose of the vaccine could potentially be given to people who’ve already had a first dose to prevent future Ebola infection. Additional trials are under way to determine the effect of a booster given at a later time, the researchers said.

Confirmation that Ervebo is safe in children, could also broaden its use. Although Johnson & Johnson’s vaccine regimen has received marketing authorisation for persons aged 1 year or older from the European Medicines Agency, licensing of the Ervebo vaccine has been limited to adults, until now. Whether its use could be expanded to children is something that the WHO’s Strategic Advisory Group of Experts on Immunization (SAGE) is likely to consider in the coming months.

SAGE may also examine whether J&J’s vaccine could be used preventively, for example to protect healthcare workers in anticipation of future outbreaks, rather than once they’ve already started.

A spokesperson for the company said: “Johnson & Johnson’s vision is to prevent outbreaks before they can begin. The Company is working collaboratively to facilitate national registrations of [its] vaccine regimen, which has been approved by the European Commission and received prequalification from the World Health Organization (WHO).