During the early stages of clinical trials with live attenuated rubella vaccines about a decade ago, two important questions were paramount in the minds of those responsible for those trials. The first was concerned with the possible communicability of the vaccine virus and the second with the duration of immunity. It must be accepted that any new vaccine poses problems, both general and specific, but as far as rubella vaccines were concerned, these were of special importance.
The first question arose from the original trials in a small group of susceptible children carried out by Parkman et al1 and Meyer et al2 with their high passage virus (HPV-77) prepared in monkey kidney cell cultures. They had shown that intermittent excretion of rubella vaccine virus occurred in the majority of vaccinated individuals. The question was simple. If vaccinees excreted virus in the nasopharynx, could infection be transmitted to susceptible