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Biomedical subjects

Robert T Chen

Publications and source records attributed to Robert T Chen.

At least 19 recordsLinked to original sources
PubMed2006

Safety of trivalent inactivated influenza vaccine in children 6 to 23 months old.

CONTEXT: Beginning with the winter season of 2004-2005, influenza vaccination has been recommended for all children 6 to 23 months old in the United States. However, its safety in young children has not been adequately studied in large populations. OBJECTIVE: To screen for medically attended events in the clinic, emergency department, or hospital after administration of trivalent inactivated influenza vaccine in children 6 to 23 months old. DESIGN, SETTING, AND PARTICIPANTS: Retrospective cohort using self-control analysis, with chart review of significant medically attended events at 8 managed care organizations in the United States that comprise the Vaccine Safety Datalink. Participants were all children in the Vaccine Safety Datalink cohort 6 to 23 months old who received trivalent inactivated influenza vaccine between January 1, 1991, and May 31, 2003 (45,356 children with 69,359 vaccinations). MAIN OUTCOME MEASURE: Any medically attended event significantly associated with trivalent inactivated influenza vaccine in risk windows 0 to 3 days, 1 to 14 days (primary analysis), 1 to 42 days, or 15 to 42 days after vaccination, compared with 2 control periods, one before vaccination and the second after the risk window. All individual ICD-9 codes as well as predefined aggregate codes were examined. RESULTS: Before chart review, only 1 diagnosis, gastritis/duodenitis, was more likely to occur in the 14 days after trivalent inactivated influenza vaccine (matched odds ratio [OR], 5.50; 95% confidence interval [CI], 1.22-24.81 for control period 1, and matched OR, 4.33; 95% CI, 1.23-15.21 for control period 2). Thirteen medically attended events were less likely to occur after trivalent inactivated influenza vaccine, including acute upper respiratory tract infection, asthma, bronchiolitis, and otitis media. After chart review, gastritis/duodenitis was not significantly associated with trivalent inactivated influenza vaccine (matched OR, 4.00; 95% CI, 0.85-18.84 for control period 1; matched OR, 3.34; 95% CI, 0.92-12.11 for control period 2). CONCLUSIONS: In the largest population-based study to date of the safety of trivalent inactivated influenza vaccine in young children, there were very few medically attended events, none of which were serious, significantly associated with the vaccine. This study provides additional evidence supporting the safety of universally immunizing all children 6 to 23 months old with influenza vaccine.

Cohort Studies↗
PubMed2005

Active telephone surveillance to evaluate adverse events among civilian smallpox vaccine recipients.

OBJECTIVE: Better characterize and monitor adverse events following Dryvax vaccinia vaccination in civilian health care workers and other first responders. DESIGN: Telephone interviews to ascertain adverse events experienced. RESULTS: Eight hundred twenty-five vaccinees, including 44 in the comparison group, were interviewed. At 10 days, 71.4% reported blisters, 35.1% reported bumps at the vaccination site, 48.5% swelling, 47.3% scab, tiredness/lethargy/fatigue (43.6%), headache (34.2%), lymph node swelling/tenderness (28.5%), muscle pain (23.1%), chills (14.4%), joint pain 11.8%, and fever >100 degrees F (12.5%). The 12.5% reported missing work because of vaccine adverse events. Most adverse events were anticipated and of short duration.

Adverse Drug Reaction Reporting Systems↗
PubMed2005

Yellow fever vaccine: an updated assessment of advanced age as a risk factor for serious adverse events.

Since 1996, the scientific community has become aware of 14 reports of yellow fever vaccine (YEL)-associated viscerotropic disease (YEL-AVD) cases and four reports of YEL-associated neurotropic disease (YEL-AND) worldwide, changing our understanding of the risks of the vaccine. Based on 722 adverse event reports after YEL submitted to the U.S. Vaccine Adverse Event Reporting System in 1990-2002, we updated the estimates of the age-adjusted reporting rates of serious adverse events, YEL-AVD and YEL-AND. We found that the reporting rates of serious adverse events were significantly higher among vaccinees aged > or =60 years than among those 19-29 years of age (reporting rate ratio = 5.9, 95% CI 1.6-22.2). Yellow fever is a serious and potentially fatal disease. For elderly travelers, the risk for severe illness and death due to yellow fever infection should be balanced against the risk of a serious adverse event due to YEL.

Adolescent↗
PubMed2005

Safety profile of smallpox vaccine: insights from the laboratory worker smallpox vaccination program.

BACKGROUND: The frequency of mild-to-moderate adverse events following smallpox vaccination was not well documented or reported during the pre-eradication era. This report describes the frequency of such symptoms among 936 adult smallpox vaccinees with and without a history of prior smallpox vaccination. METHODS: Diary cards were distributed to 1006 laboratory workers and members of the Centers for Disease Control and Prevention (CDC) smallpox response team who received smallpox vaccination under an investigational new drug protocol during 2001-2002. Vaccinees were requested to complete the diary card daily and return it to the CDC 28 days after vaccination. The proportion of vaccinees reporting symptoms was determined and compared among subgroups. RESULTS: Ninety-three percent of the diary cards were returned. The most common symptom reported was "itching at vaccination site." Primary vaccines reported statistically higher proportions of the following 11 symptoms: joint pain (25% vs. 11%; P=.0011), muscle pain (46% vs. 19%; P<.0001), fatigue (43% vs. 29%; P=.0161), swelling at vaccination site (58% vs. 33%; P<.0001), itching on the body (31% vs. 17%; P=.0048), abdominal pain (11% vs. 2%; P=.0012), swollen or tender lymph nodes (71% vs. 33%; P<.0001), pain at injection site (48% vs. 30%; P=.0018), headache (40% vs. 25%; P=.0088), backache (17% vs. 7%; P=.0090), and fever (temperature, >or=100 degrees F [37.7 degrees C]; 20% vs. 9%; P=.0047). CONCLUSIONS: This analysis suggests that previously unvaccinated persons aged <30 years experienced more symptoms than did previously vaccinated persons. The findings of increased proportions with joint pain, abdominal pain, backache, and difficulty breathing were unexpected. As with recently described cardiac adverse events, these symptoms are suggestive of systemic involvement and warrant further study.

Adolescent↗
PubMed2005

Validation of a screening instrument to identify persons for exclusion from smallpox vaccination.

Adults must be screened for atopic dermatitis and other contraindications before smallpox vaccination. We validated the sensitivity of a self-administered Centers for Disease Control and Prevention (Atlanta, GA) screening questionnaire completed by 174 hospital workers, with the workers' medical records as the reference standard. The questionnaire failed to identify one-third of the subjects who had a contraindication, although the incidence of serious adverse events has been low among vaccinees. Further assessment of screening procedures is needed if the administration of smallpox vaccine becomes more widespread in the future.

Adult↗
PubMed2005

Active surveillance of vaccine safety: a system to detect early signs of adverse events.

BACKGROUND: There currently are no population-based systems in the United States to rapidly detect adverse events after newly introduced vaccines. To evaluate the feasibility of developing such systems, we used 5 years of data from 4 health maintenance organizations within the Centers for Disease Control and Prevention (CDC) Vaccine Safety Datalink. METHODS: Within every year, each week's vaccinated children were followed for 4 weeks, and rates of adverse events were compared with rates among children of similar ages before the introduction of the new vaccine. We assessed risks for intussusception after rotavirus vaccination and risks for fever, seizures, and other neurologic adverse events after the change from whole cell diphtheria-tetanus-pertussis (DTPw) to acellular DTP vaccine (DTPa). We used sequential probability ratio testing, adjusted for age, sex, calendar time, season, and HMO, and with a stopping value based on the probability of an adverse event under the null hypothesis and under a preset alternative hypothesis. RESULTS: We detected an increase in intussusception after 2589 vaccine doses of rotavirus vaccine, about the same time initial reports of intussusception were made to the Vaccine Adverse Events Reporting System. Decreases in risk for fever, seizures, and other abnormal neurologic events became detectable within 12 weeks, 42 weeks, and 18 months, respectively, after the change from DTPw to DTPa. CONCLUSIONS: We conclude that it is feasible to develop systems for rapid and routine population-based assessments of new vaccine safety.

Databases, Factual↗
PubMed2005

Compliance with national immunization guidelines for children younger than 2 years, 1996-1999.

OBJECTIVES: To evaluate compliance with national immunization guidelines among a large cohort of children cared for at health maintenance organizations (HMOs) and to examine effects on immunization status. METHODS: A cohort study of 176134 children born between January 1, 1994, and December 31, 1997, and monitored from birth to the second birthday was performed. Subjects belonged to the Vaccine Safety Datalink Project, a study of children enrolled in 1 of 4 HMOs. Children were continuously enrolled in a HMO for the first 2 years of life. Prevailing recommendations regarding optimal ages of immunization and intervals between doses were applied to define appropriate immunization timing and immunization status. Noncompliance was defined as having a missing or late immunization or an immunization error. Immunization errors included invalid immunizations (too early to be acceptable), extra immunizations (superfluous immunizations or make-up immunizations for invalid immunizations), and missed opportunities resulting in late or missing immunizations. RESULTS: Although 75.4% of children in these HMOs were up to date for all immunizations at 2 years, only 35.6% of children were fully compliant with recommended immunization practices. Less than 8% of children received all immunizations in accordance with strict interpretation of recommended guidelines. Fifty-one percent of children had at least 1 immunization error by age 2 years; 29.7% had a missed opportunity with subsequent late or missing immunization, 20.4% had an invalid immunization, and 11.6% had an extra immunization. Common reasons for noncompliance included missed opportunities for the fourth Haemophilus influenzae type b vaccine (14.6%), invalid fourth diphtheria-tetanus-pertussis/acellular pertussis immunizations (11.0%), and superfluous polio immunizations (9.8%). CONCLUSIONS: Approximately 35.6% of children were compliant with prevailing childhood immunization recommendations from 1996 to 1999. Efforts to improve compliance with guidelines are recommended, to optimize childhood infectious disease prevention.

Cohort Studies↗
PubMed2004

Guillain-Barré syndrome following influenza vaccination.

CONTEXT: An unexplained increase in the risk of Guillain-Barre syndrome (GBS) occurred among recipients of the swine influenza vaccine in 1976-1977. Guillain-Barre syndrome remains the most frequent neurological condition reported after influenza vaccination to the Vaccine Adverse Events Reporting System (VAERS) since its inception in 1990. OBJECTIVE: To evaluate trends of reports to VAERS of GBS following influenza vaccination in adults. DESIGN, SETTING, AND PARTICIPANTS: VAERS is the US national spontaneous reporting system for adverse events following vaccination. Reports of GBS in persons 18 years or older following influenza vaccination were evaluated for each influenza season from July 1, 1990, through June 30, 2003. The number of people vaccinated was estimated from the National Health Interview Survey and US census data. Beginning in 1994, active follow-up was conducted to verify GBS diagnosis and obtain other clinical details. MAIN OUTCOME MEASURE: Reporting rates of GBS following influenza vaccination over time. RESULTS: From July 1990 through June 2003, VAERS received 501 reports of GBS following influenza vaccination in adults. The median onset interval (13 days) was longer than that of non-GBS reports of adverse events after influenza vaccine (1 day) (P<.001). The annual reporting rate decreased 4-fold from a high of 0.17 per 100,000 vaccinees in 1993-1994 to 0.04 in 2002-2003 (P<.001). A GBS diagnosis was confirmed in 82% of reports. Preceding illness within 4 weeks of vaccination was identified in 24% of reported cases. CONCLUSIONS: From 1990 to 2003, VAERS reporting rates of GBS after influenza vaccination decreased. The long onset interval and low prevalence of other preexisting illnesses are consistent with a possible causal association between GBS and influenza vaccine. These findings require additional research, which can lead to a fuller understanding of the causes of GBS and its possible relationship with influenza vaccine.

Adult↗
PubMed2004

Evaluation of vaccine safety after the events of 11 September 2001: role of cohort and case-control studies.

As immunization programs world-wide "mature" with high vaccine coverage and near elimination of vaccine-preventable disease, vaccine safety issues have increased in relative prominence. In the wake of events of 11 September 2001, fear of bioterrorism has reemerged. The paradigm of eradicating vaccine-preventable diseases, stopping vaccinations and thereby also eradicating the associated vaccine adverse events (a la smallpox) may unfortunately be obsolete. If all vaccinations have to be continued indefinitely, research is needed more than ever to understand and prevent rare vaccine adverse events. Case-control studies are usually best suited for such purposes, especially when nested within a pre-existing large-linked administrative database cohort to minimize bias. The new clinical immunization safety assessment centers may play an important role in bridging the sometimes conflicting clinical and epidemiologic perspectives in vaccine safety.

Case-Control Studies↗
PubMed2004

Use of the inactivated intranasal influenza vaccine and the risk of Bell's palsy in Switzerland.

BACKGROUND: After the introduction of an inactivated intranasal influenza vaccine that was used only in Switzerland, 46 cases of Bell's palsy were reported. METHODS: We conducted a matched case-control study and a case-series analysis. All primary care physicians, ear, nose, and throat specialists, and neurologists in German-speaking regions of Switzerland were requested to identify cases of Bell's palsy diagnosed in adults between October 1, 2000, and April 30, 2001. Each physician was invited to select three control patients for each patient with Bell's palsy, with matching according to age, date of the clinic visit, and physician. Vaccination information was provided by the physicians. RESULTS: A total of 773 patients with Bell's palsy were identified. Of the 412 (53.3 percent) who could be evaluated, 250 (60.7 percent) were enrolled and matched with 722 control patients; the other 162 patients had no controls. In the case-control study, we found that 68 patients with Bell's palsy (27.2 percent) and 8 controls (1.1 percent) had received the intranasal vaccine (P<0.001). In contrast to parenteral vaccines, the intranasal vaccine significantly increased the risk of Bell's palsy (adjusted odds ratio, 84.0; 95 percent confidence interval, 20.1 to 351.9). Even according to conservative assumptions, the relative risk of Bell's palsy was estimated to be 19 times the risk in the controls, corresponding to 13 excess cases per 10,000 vaccinees within 1 to 91 days after vaccination. In the case-series analysis, the period of highest risk was 31 to 60 days after vaccination. CONCLUSIONS: This study suggests a strong association between the inactivated intranasal influenza vaccine used in Switzerland and Bell's palsy. This vaccine is no longer in clinical use.

Administration, Intranasal↗
PubMed2004

A potential signal of Bell's palsy after parenteral inactivated influenza vaccines: reports to the Vaccine Adverse Event Reporting System (VAERS)--United States, 1991-2001.

PURPOSE: Post-licensure experience with a new intranasal inactivated influenza vaccine in Switzerland recently identified an increased risk for Bell's palsy. We reviewed reports in the Vaccine Adverse Event Reporting System (VAERS) to assess if parenteral inactivated influenza vaccines (influenza vaccines) may also increase the risk for Bell's palsy. METHODS: Reports of Bell's palsy after influenza vaccines in VAERS from 1/1/1991 to 12/31/2001 were identified by searching the Coding Symbols for Thesaurus of Adverse Reaction Terms (COSTART) for 'paralysis facial' and by text string search in the automated database. The text descriptions on each report were reviewed to verify the diagnosis. The proportional reporting ratio (PRR) was calculated to aid signal detection. RESULTS: We found a total of 197 reports of Bell's palsy after receipt of influenza vaccines. The diagnosis was verified for 154 (78.2%), of which 145 (94.2%) had received influenza vaccines alone. The verified reports were submitted from 35 states; 58% of the reports involved persons living in states where the risk of Lyme disease, which can also cause facial paralysis, was low, minimal or none. The PRRs in all age groups exceeded the criteria for a signal of possible association. The highest PRR was 3.91 in the > or = 65 years age group. CONCLUSIONS: Our findings revealed a signal of possible association between influenza vaccines and an increased risk of Bell's palsy. A population-based controlled study is needed to determine whether this association could be causal and to quantify the risk.

Adolescent↗
PubMed2004

Understanding vaccine safety information from the Vaccine Adverse Event Reporting System.

The Vaccine Adverse Event Reporting System (VAERS) is administered by the Food and Drug Administration and CDC and is a key component of postlicensure vaccine safety surveillance. Its primary function is to detect early warning signals and generate hypotheses about possible new vaccine adverse events or changes in frequency of known ones. VAERS is a passive surveillance system that relies on physicians and others to voluntarily submit reports of illness after vaccination. Manufacturers are required to report all adverse events of which they become aware. There are a number of well-described limitations of such reporting systems. These include, for example, variability in report quality, biased reporting, underreporting and the inability to determine whether a vaccine caused the adverse event in any individual report. Strengths of VAERS are that it is national in scope and timely. The information in VAERS reports is not necessarily complete nor is it verified systematically. Reports are classified as serious or nonserious based on regulatory criteria. Reports are coded by VAERS in a uniform way with a limited number of terms using a terminology called COSTART. Coding is useful for search purposes but is necessarily imprecise. VAERS is useful in detecting adverse events related to vaccines and most recently was used for enhanced reporting of adverse events in the national smallpox immunization campaign. VAERS data have always been publicly available. However, it is essential for users of VAERS data to be fully aware of the strengths and weaknesses of the system. VAERS data contain strong biases. Incidence rates and relative risks of specific adverse events cannot be calculated. Statistical significance tests and confidence intervals should be used with great caution and not routinely. Signals detected in VAERS should be subjected to further clinical and descriptive epidemiologic analysis. Confirmation in a controlled study is usually required. An understanding of the system's defined objectives and inherent drawbacks is vital to the effective use of VAERS data in vaccine safety investigations.

Adverse Drug Reaction Reporting Systems↗
PubMed2004

Lack of association between hepatitis B birth immunization and neonatal death: a population-based study from the vaccine safety datalink project.

BACKGROUND: There have been no population-based studies of the potential association between neonatal death and newborn immunization with hepatitis B vaccine (HBV). METHODS: As part of the Vaccine Safety Datalink Project, we defined a birth cohort at Southern and Northern California Kaiser Permanente Health Plans of more than 350,000 live births from 1993 to 1998 and ascertained all deaths occurring under 29 days of age. We compared the proportions of deaths among birth HBV-vaccinated and unvaccinated newborns and reviewed the causes and circumstances of their deaths. We performed detailed clinical reviews of all HBV-vaccinated neonates who died and a sample of unvaccinated neonates who died and who were matched to vaccinated deaths for days of life, sex, birth year and site of care. To avoid confounding, we categorized the causes of death as either "expected" or "unexpected" and performed a stratified analysis to compare mortality with immunization status. RESULTS: There were 1363 neonatal deaths during the study period. Whereas 67% of the entire birth cohort received HBV at birth, only 72 (5%) of the neonates who died were HBV-vaccinated at birth (P < 0.01). We found no significant difference in the proportion of HBV-vaccinated (31%) and unvaccinated (35%) neonates dying of unexpected causes (P = 0.6). Further we could not identify a plausible causal or temporal relationship between HBV administration and death for the 22 vaccinated neonates who died unexpectedly. CONCLUSIONS: A relationship between HBV and neonatal death was not identified.

California↗
PubMed2004

An analysis of rotavirus vaccine reports to the vaccine adverse event reporting system: more than intussusception alone?

BACKGROUND: The rhesus-human rotavirus reassortant-tetravalent vaccine (RRV-TV) was licensed on August, 31, 1998, and subsequently recommended for routine infant immunizations in the United States. After approximately 1 million doses had been administered, an increase in acute risk of intussusception in vaccinees led to the suspension of the use of RRV-TV and its withdrawal from the market. These postmarketing safety studies focused on a single adverse event (intussusception) and, to minimize the risk of a false-positive finding, accepted only cases that met a strict case definition. Safer rotavirus vaccines are needed to prevent the substantial global morbidity and mortality caused by rotavirus infections; their development and future use may benefit from a better understanding of the postmarketing safety profile of RRV-TV beyond intussusception. OBJECTIVE: To characterize more completely the postmarketing surveillance safety profile of RRV-TV more completely by review and analysis of Vaccine Adverse Event Reporting System (VAERS) case reports to better understand 1) whether severe adverse events other than intussusception may have occurred after RRV-TV and 2) the likely scope of gastrointestinal illnesses, of which the previously identified, highly specific intussusception cases may account for just a fraction. SETTING AND PARTICIPANTS: Infants vaccinated with RRV-TV and other vaccines in the United States and for whom a report was submitted to VAERS during September 1, 1998, to December 31, 1999. METHODOLOGY: To detect adverse events of interest other than intussusception, we used proportional morbidity analysis to compare the adverse event profile of VAERS reports among infants who received routine vaccines including RRV-TV (after excluding confirmed and suspected intussusception reports) with infants who received identical vaccine combinations but without RRV-TV. Next, to better capture all described diagnoses, signs, and symptoms associated with the suspected adverse events, a set of new codes was developed and assigned to each VAERS report. All 448 nonfatal RRV-TV-associated reports (including intussusception) were recoded manually from the clinical description on the VAERS report and categorized into clinical groups to better describe a spectrum of reported illnesses after the vaccine. Each report was assigned to one of the following hierarchical and mutually exclusive clinical groups: 1) diagnosed intussusception; 2) suspected intussusception; 3) illness consistent with either gastroenteritis or intussusception; 4) gastroenteritis; 5) other gastrointestinal diagnoses (ie, not consistent with intussusception or rotavirus-like gastroenteritis); and 6) nongastrointestinal diagnoses. RESULTS: Even after excluding intussusception cases, a higher proportion of RRV-TV reports than non-RRV-TV reports included fever and various gastrointestinal symptoms, most notably bloody stool but also vomiting, diarrhea, abdominal pain, gastroenteritis, abnormal stool, and dehydration. Distribution of RRV-TV reports by clinical groups was as follows: diagnosed intussusception (109 [24%], suspected intussusception (36 [8%]), and illness consistent with gastroenteritis or intussusception (33 [7%]), gastroenteritis (101 [22%]), other gastrointestinal diagnoses (10 [2%]), and nongastrointestinal outcomes (159 [35%]). The median time interval between vaccination and illness onset decreased incrementally among the first 4 clinical groups: from 7 days for diagnosed intussusceptions to 3 days for gastroenteritis. CONCLUSIONS: Intussusception and gastroenteritis were the most commonly reported outcomes; however, a substantial number of reports indicate signs and symptoms consistent with either illness, possibly suggestive of a spectrum of gastrointestinal illness(es) related to RRV-TV. Although VAERS data have recognized limitations such as underreporting (that may differ by vaccine) and are nearly always insufficient to prove causality between a vaccine and an adverse event, this safety profile of RRV-TV may aid better understanding of the pathophysiology of intussusception as well as development of future safer rotavirus vaccines.

Adverse Drug Reaction Reporting Systems↗
PubMed2004

The role of the Vaccine Adverse Event Reporting system (VAERS) in monitoring vaccine safety.

The role of the health professional in supporting the national passive surveillance system is essential, as the first hint of a potential problem usually originates with the astute clinician who reports a case to the appropriate source. The investigation that resulted in the voluntary withdrawal of rotavirus vaccine was triggered by nine reports to VAERS of intussuception, eight of which had occurred within 1 week of the first dose of this vaccine. Health professionals have access to the most complete information related to adverse events experienced by their patients. Any index of suspicion that a serious event or death may be related to vaccination is reason for the health professional to submit a VAERS report. Determination of whether an event was caused by the vaccine is not a prerequisite for filing a VAERS report. When in doubt, providers should report to VAERS. VAERS solicits reports for all events temporally related to vaccination, some of which may be coincidental and some of which may merely indicate a change in the frequency of expected events. Post-marketing surveillance relies on health professionals to report suspicious events, thus improving the quality of reported data and contributing significantly to safeguarding public health. Recommendations for healthcare professionals to report to VAERS recently have been incorporated into the Standards for Pediatric Immunization Practices, which are endorsed by multiple professional organizations. Despite the limitations of spontaneous reports, VAERS provides vital information of clinical importance. The identification of signals in adverse event surveillance may initiate further investigation of potential problems in vaccine safety or efficacy, and facilitate subsequent dissemination of safety-related information to the scientific community and the public. This process begins with voluntary submission of reports of possible vaccine-associated events to VAERS by the informed and conscientious health professional.

Adverse Drug Reaction Reporting Systems↗