Prime-boost Ebola vaccine yields immune response at 1 year

A prime-boost Ebola vaccine regimen that is well into clinical trials shows immune response 1 year after vaccination, the longest so far for experimental vaccines against the disease using that strategy, researchers reported today.

The trial involved two vaccine candidates, a priming dose of the adenovirus vectored Ad26.ZEBOV developed by Johnson & Johnson and a booster dose of MVA-BN-Filo from Bavarian Nordic. A team based at the University of Oxford in the United Kingdom published its findings today in the Journal of the American Medical Association (JAMA).

World Health Organization (WHO) advisors have said different types of vaccines will likely be needed to protect people against Ebola. A different vaccine, VSV-EBOV, developed by NewLink Genetics and Merck, has shown good effectiveness in clinical trials in West Africa and has emerged as the frontrunner and offers a tool for outbreak response. Health experts, however, are eyeing other strategies that are likely to afford protection over a longer period for preemptive immunization of key groups such as healthcare workers.

The Ad26.ZEBOV/MVA-BN-Filo regimen has received funding support from both the US Biomedical Advanced Research and Development Authority (BARDA) and the European Innovative Medicines Initiative Ebola + Program, a public-private consortium that includes the University of Oxford and other research groups.

Company officials have applied to the WHO for emergency use evaluation, but so far the agency hasn't announced a decision.

Phase 1 trial involved 87 adults

The new findings describe the results of a phase 1 trial at Oxford University that enrolled 87 healthy adults ages 18 to 50 years and began in December 2014. The volunteers completed the 12-month follow up in March 2016. Participants were randomized to four groups, each with 18 subjects—3 of whom received placebo and 15 who got the vaccine.

No serious events were recorded for day 240 through day 360. All of the vaccine recipients maintained Ebola-specific immunoglobulin G response at day 360. The team had previously shown that the immune response to Ebola persisted for 8 months.

Researchers said though no correlate of protection has been established yet, Ebola virus glycoprotein-specific antibodies appear to play an important role in immunity and that a preemptive strategy for using the prime-boost regimen for at-risk populations may offer advantages over single-dose vaccines.

They included the caveat that one limitation of their study is that it was conducted in a European population, in whom immune response might differ from populations in sub-Saharan Africa.

See also:

Mar 14 JAMA abstract

Mar 14 JAMA press release

Jan 17 CIDRAP News story "As Ebola interest ebbs, experts push for optimal vaccines, readiness"

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