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Biomedical subjects

R T Chen

Publications and source records attributed to R T Chen.

At least 19 recordsLinked to original sources
PubMed1999

Safety of revaccination with pneumococcal polysaccharide vaccine.

CONTEXT: Revaccination of healthy adults with pneumococcal polysaccharide vaccine (PPV) within several years of first vaccination has been associated with a higher than expected frequency and severity of local injection site reactions. The risk of adverse events associated with revaccination of elderly and chronically ill persons 5 or more years after first vaccination, as is currently recommended, has not been well defined. OBJECTIVE: To determine whether revaccination with PPV at least 5 years after first vaccination is associated with more frequent or more serious adverse events than those following first vaccination. DESIGN: Comparative intervention study conducted between April 1996 and August 1997. PARTICIPANTS: Persons aged 50 to 74 years either who had never been vaccinated with PPV (n = 901) or who had been vaccinated once at least 5 years prior to enrollment (n = 513). INTERVENTION: PPV vaccination. MAIN OUTCOME MEASURES: Postvaccination local injection site reactions and prevaccination concentrations of type-specific antibodies. RESULTS: Those who were revaccinated were more likely than those who received their first vaccinations to report a local injection site reaction of at least 10.2 cm (4 in) in diameter within 2 days of vaccination: 11% (55/513) vs 3% (29/901) (relative risk [RR], 3.3; 95% confidence interval [CI], 2.1-5.1). These reactions resolved by a median of 3 days following vaccination. The highest rate was among revaccinated patients who were immunocompetent and did not have chronic illness: 15% (33/228) compared with 3% (10/337) among comparable patients receiving their first vaccinations (RR, 4.9; 95% CI, 2.4-9.7). The risk of these local reactions was significantly correlated with prevaccination geometric mean antibody concentrations. CONCLUSIONS: Physicians and patients should be aware that self-limited local injection site reactions occur more frequently following revaccination compared with first vaccination; however, this risk does not represent a contraindication to revaccination with PPV for recommended groups.

Aged↗
PubMed1998

The Guillain-Barré syndrome and the 1992-1993 and 1993-1994 influenza vaccines.

BACKGROUND: The number of reports of influenza-vaccine-associated Guillain-Barré syndrome to the national Vaccine Adverse Event Reporting System increased from 37 in 1992-1993 to 74 in 1993-1994, arousing concern about a possible increase in vaccine-associated risk. METHODS: Patients given a diagnosis of the Guillain-Barré syndrome in the 1992-1993 and 1993-1994 influenza-vaccination seasons were identified in the hospital-discharge data bases of four states. Vaccination histories were obtained by telephone interviews during 1995-1996 and were confirmed by the vaccine providers. Disease with an onset within six weeks after vaccination was defined as vaccine-associated. Vaccine coverage in the population was measured through a random-digit-dialing telephone survey. RESULTS: We interviewed 180 of 273 adults with the Guillain-Barré syndrome; 15 declined to participate, and the remaining 78 could not be contacted. The vaccine providers confirmed influenza vaccination in the six weeks before the onset of Guillain-Barré syndrome for 19 patients. The relative risk of the Guillain-Barré syndrome associated with vaccination, adjusted for age, sex, and vaccine season, was 1.7 (95 percent confidence interval, 1.0 to 2.8; P=0.04). The adjusted relative risks were 2.0 for the 1992-1993 season (95 percent confidence interval, 1.0 to 4.3) and 1.5 for the 1993-1994 season (95 percent confidence interval, 0.8 to 2.9). In 9 of the 19 vaccine-associated cases, the onset was in the second week after vaccination, all between day 9 and day 12. CONCLUSIONS: There was no increase in the risk of vaccine-associated Guillain-Barré syndrome from 1992-1993 to 1993-1994. For the two seasons combined, the adjusted relative risk of 1.7 suggests slightly more than one additional case of Guillain-Barré syndrome per million persons vaccinated against influenza.

Adolescent↗
PubMed1998

Vaccine safety.

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Child↗
PubMed1998

Impact of anti-vaccine movements on pertussis control: the untold story.

To assess the impact of anti-vaccine movements that targeted pertussis whole-cell vaccines, we compared pertussis incidence in countries where high coverage with diphtheria-tetanus-pertussis vaccines (DTP) was maintained (Hungary, the former East Germany, Poland, and the USA) with countries where immunisation was disrupted by anti-vaccine movements (Sweden, Japan, UK, The Russian Federation, Ireland, Italy, the former West Germany, and Australia). Pertussis incidence was 10 to 100 times lower in countries where high vaccine coverage was maintained than in countries where immunisation programs were compromised by anti-vaccine movements. Comparisons of neighbouring countries with high and low vaccine coverage further underscore the efficacy of these vaccines. Given the safety and cost-effectiveness of whole-cell pertussis vaccines, our study shows that, far from being obsolete, these vaccines continue to have an important role in global immunisation.

Global Health↗
PubMed1998

Addressing the challenges to immunization practice with an economic algorithm for vaccine selection.

The biotechnology revolution is producing a growing bounty of new vaccines which pose difficult choices in selecting among many products. Some major public and private purchasers of vaccine may offer individual physicians and clinics their choice in assembling vaccine inventories. Others might purchase only a limited stock of products that would satisfactorily immunize a typical child. In either case, current vaccine selection decisions are based principally on purchase price alone without systematic consideration of other factors of fiscal consequence. As a potential tool for decision making, we developed an economic algorithm for vaccine selection that would minimize the overall costs of disease control through immunization by considering: (1) purchase price, (2) number of doses needed, (3) preparation time, (4) route of administration, (5) cold storage needs, (6) shelf life, (7) earliest age of full immunity, (8) adverse events frequency, and (9) efficacy of protection. To demonstrate the algorithm, variables (1) to (4) above were incorporated into a pilot binary-integer linear programming model that satisfied the recommended immunization schedule for diphtheria, tetanus, pertussis, Haemophilus influenzae b, and hepatitis B, using eleven vaccines (DTaP, DTaP-Hib, Hib, HepB and Hib-HepB) from four manufacturers. Five (or six) opportunities to vaccinate were modeled at (1), 2, 4, 6, 12-18, and 60 months of life, assuming US$40 per clinic visit, $15 per injection, and $0.50 per minute of nurse preparation time. Vaccine costs were varied using actual March and September 1997 US Federal vaccine prices, as well as estimates for unpriced new vaccines. Over 16,000 distinct vaccine stocking lists by vaccine type and brand were possible. Including a 1-month visit, the lowest-cost 'solution' of the algorithm was $529.41 per child in the March cost-assumption case, and $490.32 in the September one (both included four doses of DTaP-Hib, three HepB, and one DTaP). Without a 1-month visit, the lowest-cost solution in the March case cost $486.67 (four DTaP, two Hib-HepB, one DTaP-Hib, and one HepB), while the September case cost $450.32 (four DTaP-Hib, three HepB, and one DTaP). Ensuring at least one product was selected from each of the four manufacturers increased costs about $13.00, and the needed injections rose from eight to nine. The most economical selection of vaccines to use cannot be intuitively predicted, as permutations are large and solutions are sensitive to minor changes in costs and constraints. A transparent, objective selection method that weighs the economic value of distinguishing features among competing vaccines might offer the 'best value' to vaccine purchasers, while also creating strong market incentives for continuing innovation and competition in the vaccine industry.

Adolescent↗
PubMed1998

Comparative safety of two recombinant hepatitis B vaccines in children: data from the Vaccine Adverse Event Reporting System (VAERS) and Vaccine Safety Datalink (VSD).

BACKGROUND: Preliminary review of data from the Vaccine Adverse Event Reporting System (VAERS), 1991-1994, revealed that more serious adverse events were reported in children who received a specific brand of recombinant hepatitis B (HepB) vaccine. OBJECTIVE: To compare the post-marketing safety experience of the two recombinant HepB vaccines licensed for use in infants and children in the United States. DESIGN: Review of a case series derived from passive surveillance data in the national VAERS. A retrospective cohort study using data from one health maintenance organization participating in Vaccine Safety Datalink (VSD), a computerized record linkage system. POPULATIONS STUDIED: U.S. children, ages birth-10 years for whom adverse events after HepB vaccine were reported to VAERS, 1991-1994. Children, ages birth-6 years, who received HepB vaccine at Kaiser Permanente Medical Care Program, Northern California, 1991-1994. MAIN OUTCOME MEASURES: VAERS reporting rates for each vaccine by manufacturer were calculated from the numbers of reported events occurring within 30 days of HepB vaccination and the number of doses distributed by the manufacturers. VSD event rates for each vaccine were calculated from the numbers of hospitalization or emergency room visits within 30 days of HepB vaccination and the number of vaccine doses administered to the cohort. RESULTS: In VAERS, higher rates of serious events (i.e., life threatening or resulting in hospitalization or permanent disability) were reported in children who received Vaccine A vs. Vaccine B (relative risk [RR]: 3.13-8.18, P < 0.01), particularly by those vaccinated in the private (RR: 7.62-28.58, P < 0.01), but not public sector (RR: 2.12, P = 0.19). Similar types of events were reported in recipients of both vaccines. In contrast, analysis of VSD data showed no significant difference in rates of hospitalization or ER visits in children who received either HepB vaccine (RR: 0.96-1.25, P > 0.05). CONCLUSIONS: Our investigation reveals that it is unlikely there is a true difference between rates of serious events temporally associated with the two HepB vaccines in children. This study demonstrates the dual roles played by VAERS and VSD in providing a more complete picture of the post-marketing safety profile of childhood vaccines, and underscores the importance of using other analytic studies to evaluate findings from passive surveillance systems of adverse events.

Adverse Drug Reaction Reporting Systems↗
PubMed1998

Epidemiology of diarrheal disease among children enrolled in four West Coast health maintenance organizations. Vaccine Safety Datalink Team.

BACKGROUND: We used information from the Vaccine Safety Datalink (VSD) about approximately 1 million children enrolled in four health maintenance organizations to assess the morbidity from diarrhea and estimate the disease burden of rotavirus. METHODS: We examined trends of diarrhea-associated hospitalizations and emergency room (ER) visits among VSD children ages 1 month through 4 years during October, 1992, through September, 1994 (two rotavirus seasons) and estimated the morbidity from rotavirus on the basis of characteristic patterns of age and seasonality. RESULTS: Overall diarrhea was associated with 6.3% of hospitalizations and 4% of ER visits. During a child's first 5 years of life, we estimated that 1 in 57 was hospitalized and 1 in 21 required an ER visit because of diarrhea. Each year the number of diarrhea-associated hospitalizations and ER visits was greatest in winter among children ages 4 to 23 months and peaked in November in California and during February in Oregon and Washington. The winter seasonality of diarrhea-associated hospitalizations reflected the trends for diarrhea of presumed noninfectious and viral etiologies, which together accounted for most (92.9%) hospitalizations. CONCLUSIONS: Diarrhea is an important cause of morbidity among VSD children. The epidemiologic patterns of diarrhea-associated hospitalizations and ER visits resembled those reported previously for rotavirus diarrhea, suggesting that rotavirus may be a major contributor to the overall morbidity from diarrhea. Enhanced surveillance by screening for rotavirus in a sample of children with diarrhea will permit a more accurate assessment of the disease burden of this pathogen and the cost effectiveness of a rotavirus immunization program.

California↗
PubMed1998

Respiratory diphtheria in the United States, 1980 through 1995.

OBJECTIVES: The purpose of this study was to describe the epidemiologic, laboratory, and clinical features of respiratory diphtheria cases reported in the United States during 1980 through 1995. METHODS: Respiratory diphtheria cases reported to the Centers for Disease Control and Prevention were reviewed. Cases were defined as physician-diagnosed cases with signs and symptoms compatible with respiratory diphtheria, including the presence of a pseudomembrane without other apparent cause. RESULTS: From 1980 through 1994, 41 respiratory diphtheria cases were reported; none were reported in 1995, and no secondary cases were identified. Nine (22%) case patients were 4 years of age or younger, and 28 (68%) were 15 years of age or older. None of the case patients were up to date with diphtheria vaccination; 4 unvaccinated children died. Seventeen (43%) of 40 case patients had positive culture results. CONCLUSIONS: Available surveillance data suggest that respiratory diphtheria has become a rare disease in the United States. However, importation and circulation of toxigenic strains continue to present a threat and require achieving and maintaining high coverage with diphtheria toxoid-containing vaccines in both children and adults.

Adolescent↗
PubMed1997

Vaccine Safety Datalink project: a new tool for improving vaccine safety monitoring in the United States. The Vaccine Safety Datalink Team.

OBJECTIVE: To fill the large "gaps and limitations" in current scientific knowledge of rare vaccine adverse events identified in recent reviews of the Institute of Medicine. METHODS: Computerized information on immunization, medical outcomes, and potential confounders on more than 500 000 children 0 to 6 years of age is linked annually at several health maintenance organizations to create a large cohort for multiple epidemiologic studies of vaccine safety. RESULTS: Analysis of 3 years of follow-up data shows that 549 488 doses of diphtheria-tetanus-pertussis (DTP) and 310 618 doses of measles-mumps-rubella (MMR) vaccines have been administered to children in the study cohort. Analyses for associations between vaccines and 34 medical outcomes are underway. Screening of automated data shows that seizures are associated with receipt of DTP on the same day (relative risk [RR], 2.1; 95% confidence interval [CI], 1.1 to 4.0) and 8 to 14 days after receipt of MMR (RR, 3.0; 95% CI, 2.1 to 4.2). The diversity of vaccination exposures in this large cohort permits us to show that an apparent association of seizures 8 to 14 days after Haemophilus influenzae type b vaccine (RR, 1.6; 95% CI, 1.2 to 2.1) was attributable to confounding by simultaneous MMR vaccination; the association disappears with appropriate adjustment (RR, 1.0; 95% CI, 0.7 to 1.4). CONCLUSION: Preliminary design, data collection, and analytic capability of the Vaccine Safety Datalink project has been validated by replication of previous known associations between seizures and DTP and MMR vaccines. The diversity in vaccine administration schedules permits potential disentangling of effects of simultaneous and combined vaccinations. The project provides a model of public health-managed care collaborations in addition to an excellent infrastructure for safety and other studies of vaccines.

Adverse Drug Reaction Reporting Systems↗
PubMed1997

The risk of Guillain-Barré syndrome after tetanus-toxoid-containing vaccines in adults and children in the United States.

OBJECTIVES: This study examined whether there is a risk that tetanus-toxoid-containing vaccines could cause Guillain-Barré syndrome and, if so, how large the risk is. METHODS: This study was based on previous active surveillance epidemiological studies of Guillain-Barré syndrome and vaccination history. RESULTS: A background rate of 0.3 cases of Guillain-Barré syndrome per million person-weeks has been estimated. By chance, 2.2 people with the syndrome would have received tetanus-toxoid-containing vaccine within the 6 weeks before onset, yet only 1 person had done so. Data on children show similar results. CONCLUSIONS: If an association exists, it must be extremely rare and not of public health significance.

Adult↗
PubMed1997

Cumulative incidence of childhood-onset IDDM is unaffected by pertussis immunization.

OBJECTIVE: To identify a possible effect of pertussis vaccination in infancy on the risk for developing human IDDM. RESEARCH DESIGN AND METHODS: A comparison was made of the cumulative incidence of IDDM in children age 0-12 years between two birth cohorts born before pertussis vaccination and two birth cohorts born after pertussis vaccination had been excluded from the Swedish national immunization program. The Swedish Childhood Diabetes registry was used to identify cases of IDDM. Yearly nurse reports on administered vaccines were used to determine coverage for diphtheria/tetanus/pertussis (DTP) and diphtheria/tetanus (DT) vaccines. Pertussis vaccine coverage was estimated based on number of doses of vaccine made available on license. RESULTS: No difference in cumulative incidence rate of IDDM up to the age of 12 years was found when the birth cohorts for 1978 and 1979 with high DTP vaccination coverage were compared with the cohorts of 1980 and 1981 with low pertussis vaccination coverage. CONCLUSIONS: The comparison of the cumulative incidence of IDDM, up to the age of 12 years, in birth cohorts with high and low exposure to pertussis vaccine does not support the hypothesis that pertussis could induce autoimmunity to the beta-cell that may lead to IDDM.

Age Factors↗
PubMed1996

Seroprevalence of antibody against poliovirus in inner-city preschool children. Implications for vaccination policy in the United States.

OBJECTIVES: To assess susceptibility to poliomyelitis in selected inner-city preschool children in the United States and to estimate the contribution of secondary spread of live attenuated oral poliovirus vaccine virus to type-specific immunity. DESIGN: Cross-sectional seroprevalence study. METHODS: Serum neutralizing antibody levels against poliovirus types 1, 2, and 3 were analyzed according to vaccination status, age, and other sociodemographic variables. SETTING: Hospital and satellite clinics serving inner-city populations in Houston, Tex, and Detroit, Mich, 1990 to 1991. PARTICIPANTS: A total of 526 children aged 12 to 47 months seeking medical care were enrolled in the seroprevalence study; 144 children aged 12 to 35 months without a history of previous oral poliovirus vaccination were enrolled in the secondary spread study. RESULTS: Seropositive rates were similar in children in both cities, ranging from about 80% for types 1 and 3 in 12- to 23-month-old children to more than 90% in those aged 36 to 47 months. The most important predictor of seropositivity was the number of doses of oral poliovirus vaccine received (P < .01), with levels approximately 90% for all 3 serotypes among children who had received 3 or more doses. In children likely to have been unvaccinated, seropositive rates ranged from 9% to 18% for poliovirus types 1 and 3 and from 29% to 42% for type 2; secondary spread of vaccine virus appeared to have occurred among children who had previously received 1 dose or less but not those with 2 or more doses. CONCLUSIONS: Levels of immunity to poliovirus among inner-city preschoolers are high and may be predicted by the number of doses of oral poliovirus vaccine received. Secondary spread of the vaccine virus plays a modest role in increasing polio immunity in inner-city populations, especially against types 1 and 3. This role will decrease in importance if the recently attained high levels of immunization coverage in the United States are sustained and if the risk of importation of wild poliovirus continues to diminish.

Antibodies, Viral↗