LONDON — An experimental vaccine tested on thousands of people in Guinea exposed to Ebola seems to work and might help shut down the ongoing epidemic in West Africa, according to interim results from a study published Friday.

There is currently no licensed treatment or vaccine for Ebola, which has so far killed more than 11,000 people since the world's biggest outbreak began last year.

If proven effective, the vaccine could be "a game-changer," said Dr. Margaret Chan, Director-General of the World Health Organization, which sponsored the trial.

In some 4,000 people who received the vaccine within 10 days of being identified as an Ebola contact, there were no cases of the disease. That compared with 16 cases in more than 3,500 people who only got the shot after 10 days.