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In 1995, the WHO Global Programme for Vaccines and Immunization established a Vaccine Trial Registry. As of September 1996, this registry included 50 WHO-supported vaccine trials, of which 25 (50%) were completed studies. The vaccines most frequently tested have been against measles (9 trials), poliovirus (8 trials), cholera (8 trials), enterotoxigenic Escherichia coli (4 trials), and pneumococcus (4 trials). Nearly 80% of these trials have been conducted in developing countries, with the largest number being in Africa. Among the 25 completed trials, outcomes measured were immune response (24 trials), adverse reactions (13 trials), morbidity (4 trials), and mortality (1 trial). WHO's contributions to these studies include direct funding, assistance with study design, site visits, data analysis, vaccine procurement, and vaccine potency testing.In 1995, the World Health Organization (WHO) Global Program for Vaccines and Immunization established a Vaccine Trial Registry. By September 1996, 50 WHO-supported human subject vaccine trials (25 completed and 16 in progress) had been entered in this registry. Altogether, 30 candidate vaccines have been tested, including ones against measles (9 trials), poliovirus (8 trials), cholera (8 trials), enterotoxigenic Escherichia coli (4 trials), and pneumococcus (4 trials). 79% of these trials have been conducted in developing countries, primarily African. The median number of study subjects in these trials is 1022. Most frequently assessed have been immune response, adverse reactions, and morbidity. It is projected that up to 10 new vaccines will be ready for inclusion in routine immunization schedules over the next decade. WHO's contributions to this research have included direct funding, assistance with study design, site visits, data analysis, vaccine procurement, and vaccine potency testing.

In 1995-96 we conducted a review of rubella immunization strategies. Worldwide, 78 countries (more than one-third) reported a national policy of using rubella vaccine. This was closely related to country economic status. Based on the United Nations country classification, rubella vaccine is used in 92% of industrialized countries, 36% of those with economies-in-transition, and 28% of developing countries. Cases of congenital rubella syndrome (CRS) may be prevented as follows: by providing direct protection to women and/or schoolgirls (a selective vaccination strategy); by vaccinating boys and girls to provide indirect protection by reducing the transmission of rubella virus (a childhood vaccination strategy); or by a combination of these approaches (a combined strategy). A combined strategy was most commonly reported (60% of countries); seven countries (9%) reported a selective strategy; and 24 countries (31%) reported only childhood immunization. Experience has shown that it is essential to include vaccination of women of childbearing age in any rubella control strategy. Childhood vaccination alone may pose a risk of an increase in CRS cases. Although many countries have introduced rubella vaccine, few report any data on the impact of vaccination. Countries using rubella vaccine need to establish surveillance for rubella and CRS and monitor coverage in each of the target groups.

Missed opportunities for immunization are an obstacle to raising immunization coverage among children and women of childbearing age. To determine their global magnitude and reasons, studies reported up to July 1991 were reviewed. A standard measure for the prevalence of missed opportunities was calculated for each study. Seventy-nine studies were identified from 45 countries; 18 were population-based, 52 were health-service-based, and 9 were intervention trials. A median of 32% (range, 0-99%) of the children and women of childbearing age who were surveyed had missed opportunities during visits to the health services for immunization or other reasons. Missed opportunities were mainly due to failure to administer simultaneously all vaccines for which a child was eligible; false contraindications; health workers' practices, including not opening a multidose vaccine vial for a small number of persons to avoid vaccine wastage; and logistical problems. To eliminate missed opportunities for immunization, programmes should emphasize routine supervision and periodic in-service training of health workers which would ensure simultaneous immunizations, reinforce information about true contraindications, and improve health workers' practices.The authors review studies reported up to July, 1991, on the global magnitude of and reasons for missed opportunities to immunize children and women of childbearing age. A standard measure was calculated for the prevalence of missed opportunities for each of the 79 studies identified from 45 countries; 18 were population-based, 52 were health-service-based, and 9 were intervention trials. A median of 32% over a range of 0-99% children and women of childbearing age surveyed had missed opportunities during visits to health services for immunization or other reasons. These outcomes were due mainly to the future to administer simultaneously all vaccines for which a child was eligible; false contraindications; health workers' practices; and logistical problems. To eliminate these missed opportunities, programs should emphasize routine supervision and the periodic in-service training of health workers. This approach would ensure simultaneous immunizations, reinforce information about true contraindications, and improve health workers' practices.

Between February 8 and April 4, 1986, an outbreak of measles occurred in the State of Arkansas. A total of 489 suspected measles cases were reported from 53 counties; 86 schools statewide reported suspected measles cases. There were 284 cases confirmed in 18 counties; 23.6 percent among students in one university and 41.2 percent among students in kindergarten through 12th grade in 32 schools. An epidemiologic investigation was carried out to evaluate risk factors for vaccine failure and to assess the effectiveness of a selective revaccination strategy in the outbreak setting. A cohort study conducted at a junior high school showed that, compared with students vaccinated against measles at ages 15 months or older, those vaccinated at ages 12-14 months had a three-fold increased risk of measles (relative risk 3.2, 95 percent confidence interval 1.5, 6.9). For schools reporting measles, the Arkansas Department of Health and the Department of Education jointly required reimmunization of students vaccinated at ages younger than 15 months and the exclusion of students not vaccinated at ages 15 months or older until they were vaccinated or until 2 weeks after the last rash onset. To implement these recommendations, more than 100,000 doses of combined measles-mumps-rubella vaccine were distributed at a cost greater than $1 million.