- Exposure to any investigational or non-registered product (drug or vaccine) during this trial, or within 30 days prior to study enrollment. Potential subjects in the follow-up (i.e., no treatment) phase of a prior investigational study may be enrolled if the investigator's judgment is that it will have no effect on safety, reactogenicity, or immunogenicity endpoints in this study; and that it does not violate the protocol requirements of the prior trial.