Millions of doses of a candidate Ebola vaccine are expected to be available next year, with efficacy trials beginning in certain West African countries this December, the World Health Organization said this morning. There are currently two candidate vaccines for Ebola that are ready to begin human trials, and five others are expected to get started during the first several months of next year. The vaccines must be determined to be safe and effective before a mass vaccination begins, however. The WHO says that there are no plans to begin a mass vaccination program until at least June 2015, and then only if the growth of the epidemic justifies it.

The WHO cautioned that even a working vaccine would not be a “magic bullet” for stopping the spread of Ebola, according to the BBC. Rather, the WHO says that the vaccine could be a “very important tool” should the current response not be enough. “And even if the epidemic would be already receding by the time we have vaccine available, the modeling seems to say vaccine may still have an impact on controlling the epidemic,” WHO assistant director-general Marie-Paule Kieny says, according to the BBC. The WHO says that by the end of the first half of 2015, a few hundred thousand doses of candidate vaccine will be available.