The world should be far better prepared for the next Ebola outbreak, with further promising results on Tuesday showing the potential of a long-lasting vaccine against the deadly virus.
The two-part shot from Johnson & Johnson and Danish partner Bavarian Nordic induced a durable immune response lasting a full year in 100 percent of healthy volunteers vaccinated, researchers reported.
"The persistence of vaccine-induced immunity to one year post-immunization is truly impressive," said researcher Matthew Snape of the University of Oxford.
"The fact that all participants retained Ebola-specific antibodies to the end of the study does raise hope that this vaccine could induce responses that last for several years."
The vaccine requires one dose to prime the immune system and a second shot to boost the body's response.
That is different from another Ebola vaccine from Merck, which was the first to prove effective in preventing human infection during a large trial in Guinea last year.
Scientists have been racing to develop vaccines for Ebola after more than 11,300 people died in West Africa's 2013-2016 epidemic. Recent progress means experts are now confident the world will not be defenseless when the next outbreak hits.
There is debate, however, as to the best vaccination strategy for different groups at risk.
While Merck's rVSV-EBOV shot could be deployed to provide "ring vaccination" of people in recent contact with new Ebola cases, a longer-lasting option might be a better bet for healthy support workers coming in to fight the crisis.
The "prime-boost" vaccine developed by J&J and Bavarian Nordic is currently being tested in large global trials that include more than 1,000 subjects in Africa.
Results from those studies are still awaited but the vaccine has already been submitted to the World Health Organization for Emergency Use Assessment and Listing, which could allow it to be deployed on an accelerated basis in the event another Ebola crisis.
J&J said it had a stockpile of 1.8 million dosing regimens on standby in deep freeze, with the capacity to produce several million more if needed.
"We are so much more advanced now than two or three years ago," said Paul Stoffels, J&J's chief scientific officer. "We are ready to intervene if tomorrow there was a new emergency."
Keith Chappell from the University of Queensland said the data to date was encouraging, especially since the J&J vaccine was non-replicating and therefore potentially safer than the Merck shot.
The findings, based on a Phase I clinical trial involving 75 healthy subjects, were published in the Journal of the American Medical Association.
(Reporting by Ben Hirschler and Will Boggs; Editing by Mark Potter)