A population-based study of access to immunization among urban Virginia children served by public, private, and military health care systems.

BACKGROUND: Pediatric immunization rates have increased in the United States since 1990. Nevertheless, national survey data indicate that up to one third of 2-year-old children in some states and urban areas lack at least one recommended dose of diphtheria-tetanus-pertussis (DTP)-, polio-, or measles-containing vaccines. Immunization has become a key measure of preventive pediatric health care in the United States. To achieve and maintain the national immunization goal that 90% of children receive all recommended immunizations by 2 years of age, the role of the health care system in immunization delivery must be examined. Urban eastern Virginia has a diverse population that obtains immunization services from public, private, and military providers and insurers. At the time of this survey, immunization services in Virginia were available free to all children through public health clinics and to military families when using a military facility. OBJECTIVE: To examine access to pediatric immunization services and health system factors associated with underimmunization in a representative sample of children at 12 and 24 months of age. METHODS: We conducted a household survey in urban eastern Virginia from April through September 1993. A total of 12 770 households in Norfolk and Newport News, VA, were selected for inclusion in the study using probability-proportionate-to-size cluster sampling. Use of probability-proportionate-to-size sampling ensured that children within each city had equal probability of being included in the survey. Selected households were visited by trained interviewers to determine their eligibility, defined as having at least one child 12 to 30 months of age residing in the household. In eligible households, parents were asked to participate in a standardized, 15-minute interview. Survey respondents were asked about household demographics, and for each eligible child, the immunization history, health insurance, the name and location of all immunization providers, the usual immunization provider, and any problems the parent had experienced accessing immunization services with that child. Up-to-date (UTD) immunization status was defined as having all recommended doses of DTP, polio, and measles-mumps-rubella at 12 months (three DTP and two polio immunizations) and 24 months (four DTP, three polio, and one measles-mumps-rubella immunizations). The child's immunization history was assessed from parent and provider records only. Data analysis accounted for the survey's cluster sampling design (ie, within-cluster correlation). Because the immunization rates of the two cities did not differ significantly, unweighted analyses were used for ease of computation. Significance was determined for contingency tables by Wald's chi2 test. RESULTS: A total of 749 children (91% of eligible households) participated in the survey. Study children were born between October, 1990, and July, 1992. Immunization records were obtained for 705 children (94%). Eighty-seven percent of respondents were mothers, 44% were African-American, 40% of children were military dependents, and 40% were enrolled in the Women, Infants and Children (WIC) program. Sixty-five percent of children were UTD at 12 months and 53% at 24 months. Parents reported that their children's usual immunization providers were private doctors (34%); public health, hospital clinics, or community health centers (32%); and military clinics or a military contract provider (34%). At least one problem accessing immunization services was reported by 35% of respondents, ranging from 29% among those who used a private doctor as their child's usual immunization provider to 46% among those using a military contract provider. Overall, the most commonly reported problem was clinic waiting time (12%), with reports of waiting time as a problem occurring most often among those using the military contract provider (22%) and public health clinics (17%). (ABSTRACT TRUNCATED)

Mumps surveillance--United States, 1988-1993.

PROBLEM/CONDITION: CDC monitors the incidence of mumps in the United States through the passive reporting of cases to its National Notifiable Disease Surveillance System (NNDSS). REPORTING PERIOD COVERED: 1988-1993. DESCRIPTION OF SYSTEM: Weekly reports to the NNDSS from 48 states and the District of Columbia were used to calculate incidence rates for mumps. State immunization requirements were obtained from the U.S. Department of Health and Human Services. RESULTS: After the licensure of mumps vaccine in the United States in December 1967 and the subsequent introduction of state immunization laws in an increasing number of states, the reported incidence of mumps decreased substantially. The 1,692 cases of mumps reported for 1993 represent the lowest number of cases ever reported to NNDSS and a 99% decrease from the 152,209 cases reported for 1968. During 1988-1993, most cases occurred in children 5-14 years of age (52%) and in persons > or = 15 years of age (36%). Although the incidence decreased in all age groups, the largest decreases (> 50% reduction in incidence rate per 100,000 population) occurred in persons > or = 10 years of age. Overall, the incidence of mumps was lowest in states that had comprehensive school immunization laws requiring mumps vaccination and highest in states that did not have such requirements. INTERPRETATION: Because of the extensive use of mumps vaccine and the increased number of states that had enacted mumps immunization laws, the number of reported mumps cases decreased further since the marked decline that began during the early 1970s. The earlier shift in incidence from children of school ages to older persons that was noted during 1985-1988 continued until 1992, when the proportion of cases occurring in children of school ages increased and exceeded the proportions occurring in other age groups. ACTIONS TAKEN: All health-care providers are encouraged to a) report mumps cases to their local and state health departments for transmission to NNDSS and b) enact school immunization laws requiring mumps vaccination.

The geographic distribution of measles in the United States, 1980 through 1989.

OBJECTIVE: To describe the geographic distribution of measles cases in the United States by county for the 10-year period from 1980 through 1989. DESIGN: Ecological analysis of national measles surveillance data. METHODS: Measles cases reported to the Morbidity and Mortality Weekly Report from 1980 through 1989 were analyzed. Data from the 1980 and 1990 US censuses were used to produce demographic profiles for each of the 3137 countries. Outcome variables examined included mean annual incidence and number of years reporting measles, with use of Spearman's rank correlation coefficients to examine the association between the demographic and the two outcome variables. RESULTS: A total of 56,775 measles cases were reported during the decade. Of the nation's 3137 counties, 1690 (53.9%) did not report any cases; only 17 (0.5%) reported measles in all 10 years. Counties reporting measles more frequently during the decade had higher median populations, population densities, and percentage of black and Hispanic populations than those counties reporting less frequently. Population size, population density, and percentage of Hispanic population were associated with number of years reporting measles and mean annual measles incidence rate. Measles cases in counties reporting measles every year predominantly occurred in unvaccinated preschoolers; cases in counties reporting less frequently predominantly occurred in vaccinated school-aged children. CONCLUSIONS: This analysis illustrates the focal nature of measles in the United States during the past decade. Most counties have not reported a single case of measles during the entire decade, and only 17 counties reported measles every year. Targeted strategies are needed to improve age-appropriate immunization levels among preschool-aged children living in large inner-city areas.

Assessment of vital statistics and surveillance data for monitoring tetanus mortality, United States, 1979-1984.

Reported tetanus cases and tetanus deaths have declined substantially since widespread implementation of tetanus immunization. However, preventable morbidity and mortality continue to occur. During 1979-1984, 74-95 cases of tetanus were reported annually to the Centers for Disease Control (CDC) and 20-31 deaths were reported annually by the National Center for Health Statistics (NCHS). To evaluate further the health impact of tetanus, the authors assessed the completeness of national tetanus mortality data. They reviewed tetanus case report forms received at CDC from the states and NCHS multiple-cause-of-death tapes for 1979-1984. CDC reports recorded 129 deaths and NCHS mortality tapes 197 deaths. Year of death, state, age, and sex were used to match CDC and NCHS deaths, identifying 78 deaths reported to both sources. Using the methodology of Chandra Sekar and Deming, the authors estimated the actual number of tetanus deaths for 1979-1984 to be 326 (95% confidence interval 291-361). Based on this estimate, the completeness of reporting to CDC was 40%, to NCHS 60%, and to the combined systems 76%. To evaluate the reasons for underreporting, the authors contacted 14 states that had reported greater than or equal to 10 cases of tetanus to CDC during 1979-1984 to obtain death certificates for all tetanus deaths and additional information on all tetanus cases. Thirteen states submitted 108 death certificates for review. Coding and other systematic errors did not explain the low reporting efficiency. Failure to list tetanus as a cause of death on the death certificate was the primary reason for nonreporting of tetanus deaths to NCHS. These results suggest that NCHS tetanus mortality data may not be as complete as previously assumed and that tetanus mortality, and probably morbidity, are higher than previous reports have indicated.

Measles hospitalizations, United States, 1977-84: comparison with national surveillance data.

Trends in measles discharges from hospitals participating in the Commission on Professional and Hospital Activities, Professional Activities Study (CPHA-PAS) from 1977 to 1984 reflected the rapid decline in measles morbidity indicated by national surveillance data with an 88 per cent decrease in hospitalizations and a 95 per cent decrease in reported cases from 1977 to 1984. Overall trends in number, age, and seasonal distribution were also generally similar. Thirty-four per cent of the hospitalizations listed respiratory complications, 8.5 per cent otitis media, and 3.4 per cent neurologic complications.

Impact of revaccinating children who initially received measles vaccine before 10 months of age.

Two hundred fifty-four infants who had received measles vaccine at less than 10 months of age were revaccinated at greater than or equal to 15 months of age, and their immune responses were compared with 129 control infants who received their first doses of measles vaccine at greater than or equal to 15 months of age. Sera were collected at the time of revaccination (study infants) or primary vaccination (control infants), 3 weeks, and 8 months later and tested for antibody by hemagglutination inhibition (HI), enzyme-linked immunosorbent assay (ELISA), and cytopathic effect neutralization (CPEN). Of the 121 study infants who were initially HI negative, 116 (95.9%) made HI antibody 3 weeks postrevaccination compared with 126 (99.2%) of 127 control infants (P = 0.19). Of the 63 study infants with no initial detectable antibody by any of the three tests, 14 (22.2%) had a measles-specific IgM response 3 weeks postrevaccination compared with 37 of 50 (74.0%) randomly chosen control infants. By 8 months after revaccination, the 121 initially HI-negative study infants were significantly less likely to have detectable HI antibodies than control infants (52.1% v 97.6%) (P less than .001). However, 96.7% of these 121 study infants had detectable neutralizing antibody 8 months postrevaccination, an antibody thought to correlate best with protection. This study confirms the altered immune response to revaccination in infants first vaccinated prior to 10 months of age; however, the data suggest that most of these infants were successfully primed and are probably protected after revaccination.

Clinical mumps vaccine efficacy.

From February 5 through April 23, 1982, 110 cases of mumps were reported among 357 students in a middle school in Ashtabula County, Ohio, an overall attack rate of 31%. Vaccine efficacy was calculated using a variety of case definitions, case surveillance systems, and vaccination-status ascertainment methods to evaluate their effects on the estimated vaccine efficacy. From data collected at the school for case ascertainment and vaccination status, clinical vaccine efficacy was initially estimated at 37%. By means of a uniform case definition (parotitis lasting two days or more) and only cases and vaccination status ascertained from parental questionnaires, estimated vaccine efficacy increased to 70%. From secondary attack rates in household members with provider-verified vaccination status, the vaccine efficacy further increased to 85%. This outbreak investigation confirms that the methods used to ascertain cases and determine vaccination status greatly affect estimates of vaccine efficacy. Studies relying solely on school records for case finding and determination of immunization status may provide misleadingly low estimates of vaccine efficacy for mumps vaccine as well as for other vaccines. Appropriate methods demonstrate that mumps vaccine is highly effective and support recommendations for its continued use.

Field evaluation of vaccine efficacy.

PIP: This paper describes the epidemiological techniques available for measuring vaccine efficacy and recommends a practical approach to their use. The efficacy of vaccines in clinical use can be determined by a variety of means, including screening, outbreak investigations, secondary attack rates in families or clusters, vaccine coverage assessment, and case-control studies. They all offer a means of monitoring vaccine programs under conditions of day-to-day vaccine use. A table summarizes the different techniques for measuring efficacy. The screening technique is the most useful and rapid means of determining whether there is a problem with a vaccine. All that is required is a reliable estimate of the proportion of cases occurring in vaccinated individuals and an estimate of the vaccine coverage in the population at risk. If the estimated efficacy is within expected limits, more detailed studies are not warranted. If the results suggest low efficacy, more rigorous methods are necessary to assess the efficacy more accurately. Of the more accurate methods available, outbreak investigation offers the simplest means of measuring vaccine efficacy and is the preferred technique if the situation permits. The biases inherent in the method can be minimized, particularly if the disease incidence rate is high during the outbreak and accurate records exist. In large populations, the underlying immunization status prior to the outbreak can be estimated using the same cluster sampling method used in coverage assessments. Calculation of secondary attack rates in families is also an excellent and accurate means of measuring vaccine efficacy and is an acceptable alternative to the outbreak investigation. Vaccine coverage methods in endemic areas are best suited to urban areas where the measles incidence rate is high after age 11 months and low before 12 months, and maternal histories of disease are thought to be accurate. Case-control studies are best suited to areas where reliable personal immunization records may be difficult to find but other information, such as clinic records, may be available. No epidemiological method is perfect because it cannot exactly duplicate the experimental conditions of a prospective randomized clinical trial. The most accurate results will be obtained when biases are anticipated and corrective measures are taken whenever possible. Clinical vaccine efficacy determinations are carried out in order to assess whether the observed pattern of illness is consistent with the proper use of a highly effective vaccine. The components of a vaccine efficacy evaluation -- case definition, case ascertainment, and vaccination status determination -- apply to studies on all vaccines.^ieng

The opportunity and obligation to eliminate rubella from the United States.

The licensure of rubella vaccines in the United States in 1969 offered the opportunity to prevent the devastating consequences of congenital rubella infection, including miscarriages, therapeutic abortions, and congenital rubella syndrome (CRS), with its average lifetime cost of more than $220,000 per case. With the widespread use of vaccine, rubella transmission in the United States has been reduced to record low levels. Epidemics of rubella and CRS, previously reported every six to nine years, have not occurred, and since 1980, following decreases of rubella incidence rates in the postpubertal population, the endemic incidence rates of CRS have also begun to decrease. We have both the opportunity and the obligation to hasten elimination by (1) ensuring that susceptible females of childbearing age are vaccinated, (2) initiating and/or enforcing existing legislation requiring proof of rubella immunity for all children enrolled in schools, (3) intensifying surveillance for both acquired rubella and CRS, and (4) aggressively controlling rubella outbreaks.