* Initial Phase I clinical study starts in Britain
* First tests in Britain, more planned in U.S. and Africa
* J&J expects to have 2 million courses available in 2015
* Vaccine uses "prime-boost" approach involving two shots
* Bavarian Nordic shares hit highest level in four years (Adds detail on Bavarian Nordic share price gains)
By Ben Hirschler
LONDON, Jan 6 (Reuters) - Johnson & Johnson hasstarted clinical trials of its experimental Ebola vaccine, whichuses a booster from Denmark's Bavarian Nordic, makingit the third such shot to enter human testing.
The initiation of the Phase I study in Britain, which hadbeen expected about now, marks further progress in the race todevelop a vaccine against a disease that has killed more than8,000 people in West Africa since last year.
Two other experimental vaccines, one from GlaxoSmithKline and a rival from NewLink and Merck, arealready in clinical development. However, the J&J vaccine offersa different approach, since it involves two separate injections.
U.S.-based J&J said on Tuesday it had produced enoughvaccine to treat more than 400,000 people, which could be usedin large-scale clinical trials by April, and a total of 2million courses would be available in 2015. Previously, J&Jexpected more than 1 million courses this year.
It also now predicts it can make enough vaccine for 5million treatments, if required, over a 12- to 18-month period.
Just how much Ebola vaccine will be needed depends on howquickly the epidemic in Liberia, Sierra Leone and Guinea isbrought under control and declines. Currently, experts projectdemand at anywhere between 100,000 and 12 million doses.
"As long as there are still Ebola patients, there is therisk that it will continue to go around the region," PaulStoffels, J&J's chief scientific officer, told reporters.
"Does it come too late? That's going to be answered when weare there. I don't think so."
'PRIME-BOOST'
The first volunteers have received initial injections inOxford, where 72 healthy subjects will get different regimensinvolving various combinations of the vaccine components or aplacebo.
Additional clinical studies are planned in the United Stateslater this month and soon after in Africa, where volunteers willreceive the vaccine in Kenya, Uganda and Tanzania.
Phase I trials are designed primarily to test safety but mayalso indicate whether vaccines produce a good immune response.
In all, some 300 subjects will be involved in Phase Itesting, after which J&J hopes to move rapidly into largerstudies, with final-stage Phase III trials planned for thesecond quarter of 2015.
The J&J and Bavarian vaccine uses a so-called "prime-boost"approach of giving a first shot to stimulate the immune system,followed by a second booster a few weeks later.
The GSK and NewLink vaccines have been tested initially assingle shots, although there is growing debate as to whethertwo-stage vaccination might be a more strategic option, since itis likely to provide better protection. The downside is that itwould make mass immunisation more complicated.
"What we are doing with prime-boost is going for maximalprotection, as well as long-term protection," Stoffels said.
Importantly, tests have shown the J&J vaccine can be storedin a normal fridge for several months, rather than needingspecial freezing, which is difficult in rural Africa.
Shares in Bavarian Nordic, which received investment fromJ&J last year to accelerate production, rose 3.9 percent totheir highest level in four years.
Although it is too early to say how much a vaccine mightcost, the GAVI global vaccines alliance announced last month itwas committing up to $300 million to buy Ebola shots.
(Editing by Louise Heavens and Pravin Char)
Glaxosmithkline (GSK)
