The companies said they expected results from a second Phase 3 trial in a few weeks.

Next, a Phase 2 trial involves perhaps 100 patients, looking for a treatment benefit.

Finally, comes the big Phase 3 trial involving hundreds and perhaps thousands of patients around the country.

The plan is to take these vaccines into phase I human trials in the near future.

No vaccine has been tested in a phase 3 trial.

The Phase 1 trials, in which a drug's safety for patients is assessed, are complete.

"We're very enthusiastic about going forward with phase 2 trials," she said.

Early phase therapeutic trials may be available for selected patients.

However, the Phase 3 trial was halted due to safety concerns.

The one that just failed was a phase 2 trial, and three phases are usually needed for a drug to be approved.