Several of these vaccines are in or nearing large-scale clinical trials.

Two large-scale trials are under way and are expected to report results in the next couple of years.

"But we need long-term, large-scale prospective trials to actually prove that."

We currently have a large-scale trial in place to determine zinc's effect on child mortality.

Similar large-scale trials of tamoxifen will begin shortly in Europe.

So far, the idea has undergone no known large-scale trial, although that is about to change.

Three additional compounds are being considered for large-scale trials.

The Orange Farm study was the first large-scale trial to report its findings.

"We usually have only one shot at a very large-scale trial on a particular issue," he said.

Everyone agrees that large-scale trials to prove the efficacy of a vaccine will take many years.