Measles immunization with killed virus vaccine. Serum antibody titers and experience with exposure to measles epidemic. 1965.

Serum Antibody Titers and Experience With Exposure to Measles Epidemic MANY of the previous reports of children immunized with killed measles vaccine (1-5) have covered fairly short periods of observation, and the exposure of patients to a measles epidemic (wild virus infections) has been limited. In this study, the children who received the vaccine were followed for 2 to 2 1/2 years in respect to the antibody levels in their blood sera and their clinical response to exposure to measles which occurred in epidemic proportions in the community. The objectives of the study were (1) the measurement of effectiveness of killed attenuated measles vaccine in producing antibodies against the disease in susceptible children and (2) observation of the effectiveness of the vaccine in protecting the patients when they were exposed to the actual disease. A surprising development was the occurrence of atypical forms of measles in patients who had received vaccine and were subsequently exposed to epidemic clinical measles. Procedure Early in 1961, a group of 386 children attending two well-baby clinics maintained by a voluntary health agency received three intramuscular injections of 0.5 ml of vaccine administered at intervals of one month. This measles vaccine was prepared from the Edmonston strain of measles virus which was isolated and attenuated by Dr. John Enders of Boston.(6) The virus had been grown in monkey-kidney cells; and pooled samples were inactivated with formalin, concentrated, and precipitated with potassium alum. The children who received the vaccine ranged in age from 6 months to 6 years. A careful history was obtained from the parent of each child to be certain that he had not had measles previously. Serum antibody titers were measured in 90 patients, but only 80 of this group were found to be entirely free from protective antibodies prior to the attempt at immunization. Subsequent antibody determinations were made one month after the vaccine was administered, and in half of the group the test was repeated one year later. These 40 children received "booster" injections of 0.5 ml of the vaccine, and antibody titers were measured again at intervals of one month, six months (36 patients), and nine months (33 patients). Testing for neutralizing antibodies was carried out by Dr. Joel Warren and Dr. Steve Cieciura of Chas. Pfizer & Co., Inc.(7) Early in 1963 a measles epidemic developed in Cincinnati and lasted throughout the spring and summer months. In the fall of 1963 clinical histories were obtained from as many as possible of the original group of 386 children who had received the vaccine 2 to 2 1/2 years previously. A total of 313 children were available for study, and of this group 277 had had only the initial three injections of killed vaccine and the remaining 36 had had a booster injection in addition. Results Serologic Studies.--The serological response of 80 children who received the initial three injections of the killed vaccine is recorded in Table 1. There was conversion in 100% of the group. All 80 children had had no antibodies in their sera before treatment and did have detectable levels one month after the third injection. Of the 40 children available for study a year later, only nine had detectable antibody in their sera (23%). All 40 children received a single booster injection and 39 or 98% again had detectable antibody in their sera; six months later, 36 children of this group were tested and 31 or 86% still had detectable antibody, but nine months after the booster injection, only 23 of 33 children who were tested (69%) had detectable antibody in their sera. TABLE 1.--Seriological Response Following Administration of Inactivated Measles Vaccine (K) No. Patients Mo With From Detectable Start of No. …