In Reply.—Drs Wilkins and Wehrle have identified important differences between their study and ours. Their study, published in 1979, served as the impetus for us to obtain sera on children who had received rubeola vaccine before 1 year of age and were about to receive the MMR vaccine at 15 months of age. We did not obtain sera later than 52 days after MMR vaccination; therefore, we agree that our results should not be directly compared with their results indicating that 51% of 37 infants identified as vaccine failures had no detectable HI antibody by eight months after revaccination.
We would also like to address three points raised by Wilkins and Wehrle. First, some children in the vaccinated group could have experienced wild measles virus infection, although we had no history of this at the time of MMR vaccination. Second, we sought to obtain acute and convalescent sera from