Successes and failures in vaccine delivery: evaluation of the immunization delivery system in Puerto Rico.

The objective of this study was to evaluate immunization delivery and determine reasons for low coverage among preschool-age public clinic attendees in Puerto Rico. In 25 randomly selected clinics, coverage and missed immunization opportunities were assessed in 273 children aged 2 to 59 months, exist interviews were conducted with parents, and providers were interviewed. Two neighborhoods close to the clinics were surveyed to determine parental knowledge about immunizations, and the vaccination status of children in these neighborhoods was assessed. Two hundred seventy-three clinic attendees were interviewed. Among 229 (84%) with vaccination cards, only 126 (55%) had received all indicated vaccines by completion of the clinic visit. Forty-five percent of children with cards in the household survey were not up-to-date. Of 171 (75%) clinic attendees eligible for vaccination at the visit, 118 (69%) missed one or more immunizations at the visit. In addition, half of all children had previously missed one or more immunizations when they had received another vaccine. Missed opportunities occurred because of nonavailability of vaccines, lack of integration of services, provider misconceptions about contraindications, and failure to administer vaccines simultaneously. Other problems included barriers to immunization services and lack of information and education activities. It is concluded that deficiencies in immunization delivery substantially delay immunization and reduce coverage.

Determinants of vaccination in an urban population in Conakry, Guinea.

A community survey was conducted in 1989 in Conakry, Guinea to determine reasons for low vaccination coverage. Some 377 children aged 12-23 months and their guardians were studied, of whom 204 (54%) had vaccination records. According to their records 19% of children were fully and correctly vaccinated. Thirty-nine incompletely vaccinated children (19% of those with records) had sufficient documented contacts with health services to be fully vaccinated, but at least one immunization opportunity was missed. Multivariate analyses were conducted to identify factors associated with receipt of first dose diphtheria/pertussis/tetanus/oral polio vaccine (DPT/OPV) and with completion of the DPT/OPV series. Factors determining initiation of the series included maternal education (assessed by ability to speak French), household possession of a television, maternal age less than 35 years, child's birth in hospital, and, for non-French speakers, the mother considering vaccination to be affordable. Factors determining completion of the DPT/OPV series, among children who began vaccination, included maternal education, employment, and past positive experience with vaccination services (short waiting times, not having been turned away from vaccination, and not knowing a child with a post-vaccine 'abscess'). Vaccination coverage can be substantially increased in Conakry by improving health services to avoid missed opportunities, following the vaccination schedule correctly, reducing waiting times and avoiding abscesses.

Paralytic poliomyelitis in Oman: association between regional differences in attack rate and variations in antibody responses to oral poliovirus vaccine.

Variation in attack rates of paralytic disease by region during the 1988-1989 epidemic of type 1 poliomyelitis in Oman provided the stimulus to test the hypothesis that these observations were due to regional differences in the response of infants to trivalent oral poliovirus vaccine (OPV). Seroprevalence studies of 394 children born during the outbreak were conducted in six different regions of Oman and in two socioeconomic status (SES) groups in the capital city of Muscat; a seroconversion study was also carried out in 105 infants born after the outbreak. Seroprevalence rates by region after receipt of at least three doses of OPV ranged from 90% to 100% (median 94%) to poliovirus type 1, and from 86% to 100% (median 97%) to type 2, and from 47% to 79% (median 72%) to type 3, with the lowest rates observed in regions with the highest incidence of type 1 paralytic disease. In Muscat, seroprevalence rates were also significantly lower in low versus high SES groups (type 1: 84% versus 98%, respectively [P = 0.006]; type 3: 59% versus 86%, respectively [P = 0.001]). In the seroconversion study conducted after the outbreak, 89%, 100% and 50% of infants had detectable antibodies to types 1, 2, and 3, respectively, after four doses of OPV. Low responses to type 3 were also associated with the occurrence of sporadic cases of type 3 poliomyelitis in 1991, in spite of high rates of coverage with at least four doses of OPV (> 96%) throughout the country.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential impact on vaccination coverage levels by administering vaccines simultaneously and reducing dropout rates.

BACKGROUND: Retrospective immunization coverage surveys conducted during 1991 and 1992 demonstrated that coverage levels for the routine childhood vaccines by 24 months of age in selected urban areas of the United States ranged from 10% to 52%, far below the US Public Health Service goal of 90%. Therefore, appropriate programmatic changes must be identified and incorporated. METHODS: We analyzed coverage survey data collected from 21 sites to measure the potential impact on coverage levels of implementing selected changes in vaccination practices. In a multistaged cluster survey design, school health records of kindergarten or first-grade students were randomly selected and dates of vaccination assessed. We evaluated changes in the vaccination practices, such as eliminating missed opportunities for simultaneous administration of vaccines and ensuring that children initiated the vaccination series on time (ie, by 3 months of age). We then calculated potential increases in coverage levels for a best-case scenario. RESULTS: From 77% to 96% of all children in the 21 sites had received at least one vaccination by their first birthday. Children were 2.3 to 17 times more likely to be up to date on their vaccinations by 24 months of age if they were up to date at 3 months of age. Each child had many opportunities for the simultaneous administration of diphtheria and tetanus toxoids and pertussis (DTP) vaccine, oral polio vaccine (OPV), and measles-mumps-rubella (MMR) vaccine that, if used appropriately, could have potentially raised coverage levels by 12% to 22% (median, 17%). The highest coverage levels could have been attained if all children had started the series on time and if advantage had been taken of all opportunities for simultaneous vaccination. Coverage levels for four doses of DTP vaccine, three doses of OPV, and one dose of MMR vaccine would have increased from a baseline of 10% to 52% to levels of 54% to 83%. CONCLUSIONS: Although the majority of children received a vaccination by their first birthday, the coverage level at 24 months of age was low. Tracking systems are needed to ensure that children do not drop out of the system once they have begun the vaccination series. In addition, all children who are late in beginning their vaccination series are at increased risk of not completing the recommended vaccination series on time, and these children need intensive follow-up and recall efforts. Also, providers need to administer all needed vaccines simultaneously.

Forty years and four surveys: how does our measuring measure up?

OBJECTIVE: This article reviews four surveys methodologies that have been used over the past 40 years to assess immunization rates in young children in the United States. These methods include three national surveys: (1) United States Immunization Survey (1959-1985), which was first a household and then a telephone survey; (2) National Health Interview Survey (1991-present), which interviews people in their homes; and (3) National Immunization Survey (1994-present), a random-digit-dialing telephone survey. In addition, a series of retrospective school record surveys that used standard sampling and assessment methodologies were conducted nationally during 4 school years September 1990-May 1991. METHODS: Federal publications, National Immunization Conference proceedings, and Centers for Disease Control and Prevention (CDC) internal reports regarding national immunization surveys were reviewed. The methodology used in each survey is presented, and selected examples of previously tabulated results are presented. CONCLUSIONS: The assessment of immunization coverage in American preschool children requires ongoing commitment and survey expertise. Over the past 40 years the CDC's efforts to determine vaccination coverage in young children has evolved from the comparatively simple United States Immunization Survey to the current National Immunization Survey that utilizes sophisticated statistical and survey techniques to obtain the most-accurate results yet available.

National Immunization Survey: the methodology of a vaccination surveillance system.

The National Immunization Survey (NIS) was designed to measure vaccination coverage estimates for the US, the 50 states, and selected urban areas for children ages 19-35 months. The NIS includes a random-digit-dialed telephone survey and a provider record check study. Data are weighted to account for the sample design and to reduce nonresponse and non-coverage biases in order to improve vaccination coverage estimates. Adjustments are made for biases resulting from nonresponse and nontelephone households, and estimation procedures are used to reduce measurement bias. The NIS coverage estimates represent all US children, not just children living in households with telephones. NIS estimates are highly comparable to vaccination estimates derived from the National Health Interview Survey. The NIS allows comparisons between states and urban areas over time and is used to evaluate current and new vaccination strategies.

Outbreaks in highly vaccinated populations: implications for studies of vaccine performance.

Most of the factors associated with the failure of a vaccination to provide protective immunity are not distributed uniformly or randomly within populations. This paper explores the extent to which a nonrandom distribution of vaccination failures and the selection of exceptional situations for investigation may influence estimates of vaccine performance. The authors show that outbreak investigations will tend to underestimate vaccination efficacy, and that the extent of underestimation will be related directly to the size of the epidemic triggering an investigation, the vaccination coverage in the community, and the extent of clustering of vaccination failures in the population; it will be related inversely to the size of and contact intensity within the investigated community. These potential sources of bias are not the only problems that arise in estimating vaccine efficacy, but they should be taken into consideration when analyzing and interpreting outbreak situations. The fact that outbreak investigations carried out within the United States during the past decade have provided estimates of measles vaccination efficacy on the order of 95% is consistent with a somewhat higher overall "true" efficacy of current vaccines and procedures in the total population. It is important to understand better the frequency, distribution, and risk factors for vaccination failures in populations.

Obstacles to achieving immunization for all 2000: missed immunization opportunities and inappropriately timed immunization.

Missed opportunities and inappropriately time immunization substantially reduced the coverage achieved in Mozambique and Guinea Conakry. During coverage surveys in Mozambique, we noted dates of attendance at a health facility for growth monitoring or vaccination, and in Conakry we also abstracted dates of curative care visits from home-based documents. In Mozambique, an average of 84 per cent of children aged 12-23 months had documents, and an average of 53 per cent of children were fully and correctly vaccinated. Among children with cards, 11 per cent had received all vaccines, but at least one dose was applied before the recommended age or with too short an interval between doses (inappropriately timed vaccinations). A further 8 per cent of children had sufficient documented contacts with preventive services to be fully vaccinated, but immunization opportunities had been missed. In Conakry, 54 per cent of 12-23 month-old children had immunization cards, and only 19 per cent were fully and correctly vaccinated. Among children with cards, 9 per cent had received all vaccines, but some were inappropriately timed, and 19 per cent had enough contacts with curative or preventative services to be fully vaccinated, but opportunities had been missed. We recommend that home-based records document all health centre visits, including those for curative care, and that missed opportunities and vaccination timing be routinely evaluated during vaccine coverage surveys.

Low vaccination levels of US preschool and school-age children. Retrospective assessments of vaccination coverage, 1991-1992.

OBJECTIVE: To obtain estimates on (1) the percentage of children who were up-to-date on the recommended childhood vaccination series, (2) the percentage of children who were age-appropriately immunized, and (3) coverage levels by individual vaccines. DESIGN: Vaccination levels were estimated by conducting retrospective immunization coverage surveys of the school health records of children entering kindergarten or first grade in the 1990-1991 or 1991-1992 school year. A multistage cluster survey design was used. SETTING: Survey sites were selected from among the 60 largest urban areas in the United States. One small city and one rural area were selected for comparison. RESULTS: By their second birthday, 11% to 58% (median, 44%) of the children were fully vaccinated. Stricter measurement criteria lowered coverage levels further. Completed series levels at school entry were 71% to 96% (median, 87%). CONCLUSIONS: Vaccination levels at the second birthday were far below the goal for the year 2000. All health providers need to administer vaccines according to the recommended schedule.

Mortality from pneumonia in children in the United States, 1939 through 1996.

BACKGROUND AND METHODS: Pneumonia remains an important cause of childhood deaths throughout the world, but in developed countries, the mortality rate is decreasing. We reviewed death records for children in the United States from 1939 through 1996. A plot of the annual rates of change in the number of deaths from pneumonia was used to generate hypotheses about the influence of various events and interventions. We used data from the National Hospital Discharge Survey, the Medicaid program, and published reports to test these hypotheses. RESULTS: During the 58-year study period, the number of children who died from pneumonia declined by 97 percent, from 24,637 in 1939 to 800 in 1996. During the same period, the rate of mortality from other causes declined by 82 percent. There were steep declines in the mortality rates for pneumonia from 1944 to 1950, although the rate increased among older children in 1957, and there were sustained declines in all age groups from 1966 to 1982. From 1966 to 1982, the mortality declined by an average of 13.0 percent annually, and these decreases coincided with increases in the proportion of poor children covered by Medicaid, increases in rates of hospitalization for pneumonia, a narrowing of the gap between the mortality rate for black children and the rate for white children, and a convergence between the mortality rate in the South and the rates in the other three census regions. CONCLUSIONS: Since 1939, the rate of mortality from pneumonia in children in the United States has declined markedly. We hypothesize that the steep declines in the late 1940s are attributable to the use of penicillin, that the peak in 1957 was due to the influenza A pandemic, and that the sustained decline from 1966 through 1982 may be attributable in part to improved access to medical care for poor children.

A profile of mothers giving birth to infants with congenital rubella syndrome. An assessment of risk factors.

To formulate strategies for elimination of congenital rubella syndrome, it is important to identify risk factors for delivering an infant affected by it. We analyzed cases of congenital rubella syndrome in infants born from 1970 to 1985 and reported to either one of two independent Centers for Disease Control surveillance systems. Mothers of infants with congenital rubella syndrome identified in both surveillance systems were disproportionately younger than mothers giving birth in the United States. The risk for delivering an infant with congenital rubella syndrome was approximately 2.5 times higher for blacks compared with whites for both reporting systems. A total of 18% of infants with congenital rubella syndrome born since 1979 were Hispanic (national population average, 7%). Both surveillance systems showed that, although primiparous mothers were at highest risk, 39% of women delivering infants affected by congenital rubella syndrome had had at least one previous live birth, suggesting that postpartum immunization could have prevented these congenital rubella syndrome cases. Young, black, and Hispanic primiparous women represent populations at elevated risk for delivering a congenital rubella syndrome-affected infant and should be specifically targeted for immunization.

Immunogenicity of high-titre AIK-C or Edmonston-Zagreb vaccines in 3.5-month-old infants, and of medium- or high-titre Edmonston-Zagreb vaccine in 6-month-old infants, in Kinshasa, Zaire.

The effect of measles vaccine potency was evaluated among 485 children aged 6 months, and the effect of vaccine strain was evaluated among 538 children aged 3.5 months, in Kinshasa, Zaire. Children aged 6 months were randomly assigned to receive either high-titre Edmonston-Zagreb (EZ-H), potency 5.7 log10/dose, or medium-titre EZ (EZ-M), potency 4.7 log10/dose, those aged 3.5 months were randomly assigned to receive either AIK-C, potency 5.5 log10/dose, or EZ-H, and were revaccinated with EZ-M vaccine at age 9.5 months. Measles antibodies were measured using the plaque reduction neutralization assay. Among children vaccinated at age 6 months, the seroresponse was significantly higher after EZ-H than EZ-M vaccine, with 92 and 83% seroconverting by 6 months postvaccination and 59 and 40% respectively having antibody titres > 200 mIU. Among children vaccinated at age 3.5 months, only 24% (AIK-C) and 22% (EZ-H) attained antibody titres > or = 200 mIU 6 months postvaccination. After revaccination at age 9.5 months, 81% of children in the AIK-C group and 73% in the EZ-H group had antibody levels > 200 mIU (p = 0.056). A retrospective survey was conducted in January 1993 to determine the mortality experience of vaccine groups, and information was obtained for 94% of the children. A total of 44 deaths (4%) were identified, with no significant differences between groups when stratified by age at vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring progress toward US preschool immunization goals.

The United States has achieved over 97% immunization of children by school age and has reduced the incidence of vaccine-preventable diseases by more than 90% since the prevaccination era. However, children often do not receive immunizations at the recommended age, and in densely populated urban areas this delay in immunization has led to epidemics of measles. Correctable deficiencies of the immunization delivery system have been identified in these areas. To respond to needs, the public health infrastructure must be strengthened, and active participation from the private sector must be obtained, both in delivery of immunizations and in assessment of performance. Appropriate action must be stimulated by the provision of timely information on immunization coverage and on indicators of program performance at the local level.

Pertussis surveillance--United States, 1989-1991.

The licensure of whole-cell pertussis vaccine combined with diphtheria and tetanus toxoids as DTP in the 1940s--and its widespread use in infants and children--led to a dramatic decline in the incidence of reported pertussis. In the prevaccine era, the average annual incidence and mortality for reported pertussis were 150 cases and six deaths per 100,000 population, respectively. From 1989 to 1991, pertussis cases were reported by state and local health departments to CDC through two distinct national surveillance systems: the National Notifiable Diseases Surveillance System (NNDSS) and the Supplementary Pertussis Surveillance System (SPSS). During the period 1989-1991, 11,446 pertussis cases were reported to the NNDSS (4,157 in 1989; 4,570 in 1990; and 2,719 in 1991), for an unadjusted annual incidence of 1.7, 1.8, and 1.1 cases per 100,000 population in 1989, 1990, and 1991, respectively. For the period 1989-1991, case reports were received through the SPSS on 9,480 (83%) of the 11,446 patients reported to the NNDSS. Age-specific incidence and hospitalization rates were highest among children < 1 year of age and declined with increasing age. Long-term trends suggest an increase in the reported incidence of pertussis in the United States since 1976. The peak in reported pertussis cases in 1990 represents the highest annual incidence of pertussis since 1970. However, the incidence of pertussis declined 41% from 1990 through 1991. Whether the long-term increase in reported pertussis is a true increase in incidence is unclear; the observed increase may be a function of improved surveillance.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiological features of pertussis in the United States, 1980-1989.

From 1980 through 1989, 27,826 cases of pertussis were reported to the Centers for Disease Control, for an average annual crude incidence of 1.2 cases/100,000 population. The incidence of reported disease increased in all age groups during this period, but the increase was disproportionately large among adolescents and adults. Infants between 1 and 2 months of age were at highest risk for pertussis (average annual incidence, 62.8/100,000). Infants less than 2 months of age had the highest reported rates of pertussis-associated hospitalization (82%), pneumonia (25%), seizures (4%), encephalopathy (1%), and death (1%). Rates of complication were generally higher among unvaccinated children than among those who had received three or more doses of diphtheria-tetanus-pertussis vaccine; 64% of children 3 months to 4 years of age who had reported cases of pertussis had not been immunized appropriately for their age. Whereas control of pertussis in the United States may be further improved through increased levels of diphtheria-tetanus-pertussis vaccination among eligible infants and children, the use of acellular vaccines in adolescents and adults may also be needed to reduce the burden of pertussis in very young infants.

Surveillance for meningococcal disease and strategies for use of conjugate meningococcal vaccines in the United States.

BACKGROUND: Neisseria meningitidis is a leading cause of bacterial meningitis in US; new capsular type-specific conjugate vaccines offer an opportunity for improved control of meningococcal disease. We evaluated the relative burdens of invasive meningococcal disease in US and examined the projected impact of various meningococcal conjugate vaccination strategies on rates of meningococcal disease. METHODS: Meningococcal disease incidence rates were determined from active, population-based surveillance in selected US areas. Models were created to determine impact of vaccination of infants, toddlers, adolescents or college students with meningococcal conjugate vaccines, with assumptions for vaccine coverage, efficacy and duration of protection. Although we examined possible conjugate vaccine formulations including serogroups A, C, Y and W-135, the final vaccine impact analysis excluded serogroups A and W-135. Outcome measures were cumulative meningococcal disease incidence, and incidence 10 years after initiating vaccination among 0-22-year-olds. RESULTS: In models of serogroup C+Y meningococcal conjugate vaccination of infants, toddlers and adolescents, the cumulative incidence of meningococcal disease was reduced by 54, 48 and 25%, respectively; the toddler strategy had the greatest impact per dose. After 10 years of routine meningococcal conjugate vaccination, meningococcal disease could be reduced by 50% and deaths by 64%. CONCLUSIONS: Use of meningococcal conjugate vaccine could markedly reduce meningococcal disease incidence. Our data, along with vaccine formulation and vaccination program considerations, will be important in determining the optimal choice of vaccination strategy.

Measles among the Amish: a comparative study of measles severity in primary and secondary cases in households.

An outbreak of measles among a predominantly unvaccinated and susceptible Amish population in Lebanon County, Pennsylvania, offered the opportunity to test the hypothesis that secondary cases in households are more severe than primary cases because the former have more intense exposure and receive a greater virus inoculum. Of 130 measles cases reported between April and June 1988, 119 (92%) constituted a study of disease severity. Severity was assessed by determining frequency and duration of symptoms, length of any hospitalization, and number of days in bed. In a univariate analysis, fewer secondary cases had conjunctivitis (relative risk [RR], 0.67; 95% confidence interval [CI], 0.48-0.96) and headache (RR, 0.37; CI, 0.15-0.86), but more had earache (RR, 9.69; CI, 1.8-202.9) compared with primary cases. Secondary cases had a shorter mean duration of coryza (4.0 vs. 5.0 days, Student's t test, P = .08). However, a logistic regression model that matched by family and controlled for age and sex indicated that there were no significant differences in measles severity among primary and secondary cases in households.

Comparison of two commercial microimmunofluorescence kits and an enzyme immunoassay kit for detection of serum immunoglobulin G antibodies to Chlamydia pneumoniae.

We compared the MRL and the Labsystems Chlamydia pneumoniae microimmunofluorescence (MIF) immunoglobulin G (IgG) kits and the Labsystems enzyme immunoassay (EIA) kit in a blinded study of 83 serum samples in which we evaluated titers, cross-reactivity to other species, and reproducibility. There was no statistically significant difference between the MRL and the Labsystems MIF kits in the endpoint titers of IgG antibody to C. pneumoniae. The correlation between the results obtained with these two MIF kits was excellent (r = 0.95; P = 0.001). The cross-reactivity of the C. pneumoniae-positive sera with C. trachomatis- and C. psittaci-positive sera was assessed for each MIF kit. For C. pneumoniae-positive sera with titers of > or =32, the Labsystems MIF kit exhibited more cross-reactivity to C. psittaci than the MRL kit did. The values obtained with the Labsystems EIA kit represented single dilutions of serum specimens expressed as enzymeimmuno units on a continuous scale. The results obtained with the Labsystems EIA kit correlated moderately well with those obtained with each MIF kit when they were compared for their abilities to detect IgG antibodies to C. pneumoniae (for the MRL MIF kit, r = 0.79 [P = 0.001]; for the Labsystems MIF kit, r = 0.78 [P = 0.001]). The results obtained with the commercial MRL and Labsystems MIF kits and the Labsystems EIA kit tested were reproducible; and the kits were standardized, had quality control reagents, and are suitable for detection of C. pneumoniae antibodies in serum and for use in interlaboratory studies. Validation of the use of these kits for clinical diagnosis still needs further evaluation.