- Chickenpox or measles A subject is not eligible if he/she currently has chickenpox or measles, or has been exposed to chickenpox or measles during the last three weeks and is non-immune. If a subject develops chickenpox or measles during the study, he/she will be withdrawn from the study. If a non-immune subject is exposed to chickenpox or measles during the study, his/her continuation in the study will be at the discretion of the investigator, taking into consideration the likelihood of developing active disease.