The regulatory agencies and drug companies are caught between a rock and a hard place when epidemiologic associations between drugs and adverse events result in the suspension or withdrawal of a marketed product, even when no causal connection has been established, sometimes leaving affected populations with no alternative treatment.

Wyeth Lederle Vaccines, a business unit of Wyeth-Ayerst Laboratories, is the latest company dealing with an as yet unproven epidemiologic association. Looking at data collected through its Vaccine Adverse Event Reporting System, the U.S. Centers for Disease Control and Prevention grew jittery