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.

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.

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.

National Immunization Information Hotline: Calls concerning adverse events, 1998-2000

Data from the National Immunization Information Hotline (NIIH) concerning vaccine adverse event inquiries were analyzed from 1998 to 2000 (total n = 23,841 [public n = 14,330; health care professionals n = 9,511]). Approximately 20% of calls from the public from 1998 to 2000 concerned vaccine adverse events. These calls increased 199.5% from 1998 (n = 422) to 1999 (n = 1,264), then declined 12.4% from 1999 to 2000 (n = 1,107). A Lexus Nexus search showed that the number of news stories mentioning vaccine safety showed a similar pattern. Women were more likely to call the NIIH concerning vaccine adverse events than men, and persons 40-59 years old and persons 60 years old and over were less likely to call about vaccine adverse events than those 20-39 years. The parallel trends in news stories mentioning vaccine safety and calls to the NIIH concerning adverse events suggests that news stories may stimulate questions about vaccine safety. Understanding that news stories may elicit questions about vaccine adverse events and examining the characteristics of persons who ask vaccine adverse event questions may guide future informational interventions toward those most in need.

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.

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.

The National Immunization Information Hotline

The National Immunization Information Hotline (NIIH) has been providing information regarding immunizations to the public and to health care professionals since March 1997. We describe the operations of the NIIH, its experience over the first two and a half years of operation and lessons learned for other immunization hotlines. From 1998-2000, the hotline answered 246,859 calls. Calls concerning immunization information requests totaled 175,367; data about the calls were collected from 35,102. Approximately a third of the 35,102 calls were from health care providers. Of the remaining calls from the public, the greatest number of calls concerned childhood immunizations. Immunization schedule queries from the public increased 323.0% from 1998 to 2000. While the major goal of the NIIH is to provide accurate and reliable information to the public and to health care providers, data from the hotline can be used to monitor changes over time in calls concerning inquiries about the immunization schedule in addition to other variables of interest.

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.

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.

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.

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.

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.

Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases

OBJECTIVE

To assess the possible toxicity of thimerosal-containing vaccines (TCVs) among infants.

METHODS

A 2-phased retrospective cohort study was conducted using computerized health maintenance organization (HMO) databases. Phase I screened for associations between neurodevelopmental disorders and thimerosal exposure among 124 170 infants who were born during 1992 to 1999 at 2 HMOs (A and B). In phase II, the most common disorders associated with exposure in phase I were reevaluated among 16 717 children who were born during 1991 to 1997 in another HMO (C). Relative risks for neurodevelopmental disorders were calculated per increase of 12.5 micro g of estimated cumulative mercury exposure from TCVs in the first, third, and seventh months of life.

RESULTS

In phase I at HMO A, cumulative exposure at 3 months resulted in a significant positive association with tics (relative risk [RR]: 1.89; 95% confidence interval [CI]: 1.05-3.38). At HMO B, increased risks of language delay were found for cumulative exposure at 3 months (RR: 1.13; 95% CI: 1.01-1.27) and 7 months (RR: 1.07; 95% CI: 1.01-1.13). In phase II at HMO C, no significant associations were found. In no analyses were significant increased risks found for autism or attention-deficit disorder.

CONCLUSIONS

No consistent significant associations were found between TCVs and neurodevelopmental outcomes. Conflicting results were found at different HMOs for certain outcomes. For resolving the conflicting findings, studies with uniform neurodevelopmental assessments of children with a range of cumulative thimerosal exposures are needed.

Adverse event reporting rates following tetanus-diphtheria and tetanus toxoid vaccinations: data from the Vaccine Adverse Event Reporting System (VAERS), 1991-1997

Since 1966, the Advisory Committee on Immunization Practices (ACIP) has recommended tetanus-diphtheria toxoid (Td) be used instead of single antigen tetanus toxoid (TT) because, while both vaccines protect against tetanus, only Td protects against diphtheria. Despite this recommendation, approximately 2.5 million doses of TT were distributed annually from 1991 to 1997. One possible explanation for the continued use of TT is concern about the relative safety of Td. Small clinical trials found Td to be associated with a higher rate of local vaccine-associated adverse events (VAEs) than TT. To determine if the findings from the trials would hold up on a larger scale, we compared the rate of reporting to the Vaccine Adverse Event Reporting System (VAERS), a passive reporting system, after either vaccine from 1991 to 1997. There were 40 reports per million doses of Td, and 27 reports per million doses of TT, for a reporting rate ratio of 1.4. Reporting rates to VAERS are lower than the rates of VAEs identified in the clinical trials, but the magnitude of the difference in VAEs following TT versus Td is similar. While reporting rates are lower after TT than Td, rates of reported VAEs after both vaccines are low.

A retrospective cohort study of the association of varicella vaccine failure with asthma, steroid use, age at vaccination, and measles-mumps-rubella vaccination

OBJECTIVE

Varicella breakthrough, the occurrence of varicella disease >42 days after vaccination, is indicative of vaccination failure. A sevenfold increased risk of breakthrough among vaccinated children with asthma was observed in a 1996 varicella outbreak in a child care center. More recent outbreak investigations have also identified age at vaccination as a potential risk factor for breakthrough. We assessed the association of varicella breakthrough with asthma, steroids, age at varicella vaccination, and timing of measles-mumps-rubella (MMR) vaccination.

METHODS

We performed a retrospective cohort study among children born after 1993 and followed up through 1999 at 2 health maintenance organizations ([HMOs] A and B) in the United States. Information was obtained from automated vaccination, clinic, hospital discharge, and pharmacy records.

RESULTS

We identified 268 and 97 breakthrough cases among 80 584 and 8181 children vaccinated against varicella at HMOs A and B, respectively. Varicella breakthrough was not associated with asthma, inhaled steroids prescribed at any time, and oral steroids prescribed before vaccination. An increased risk of varicella breakthrough was found in the 3 months immediately after prescription for oral steroids at HMO A (adjusted relative risk [aRR]: 2.4; 95% confidence interval [CI]: 1.3-4.4) and HMO B (aRR: 2.8; 95% CI: 1.0-7.8), when varicella vaccine was given before 15 months of age at HMO A (aRR: 1.4; 95% CI: 1.1-1.9), and when varicella vaccination followed MMR vaccine within 28 days at HMO A (aRR: 3.1; 95% CI: 1.5-6.4).

CONCLUSIONS

Varicella vaccine failure in children was not associated with asthma or the use of inhaled steroids, but with the use of oral steroids. Administration of varicella vaccine before the age of 15 months may be associated with a slightly increased risk of breakthrough disease. As currently recommended, varicella vaccination should not be administered for 28 days after MMR vaccination.

Eczematous skin disease and recall of past diagnoses: implications for smallpox vaccination

BACKGROUND

Persons with atopic dermatitis or eczema, regardless of disease severity or activity, may develop eczema vaccinatum if they or their close contacts receive the smallpox vaccine. According to current recommendations, a preexposure vaccination program should identify these persons and exclude them from participating.

OBJECTIVE

To determine the prevalence of diagnosed atopic dermatitis and eczema in a defined population and assess the sensitivity of screening questions to identify patients who have received these diagnoses.

DESIGN

Population-based prevalence survey and telephone interview.

SETTING

14 ZIP code regions in Wisconsin.

PATIENTS

Persons given a diagnosis of atopic dermatitis or eczema in 2000 and 2001 were identified from a population-based cohort. Persons with a history of atopic dermatitis diagnosed since 1979 were eligible for the telephone survey.

MEASUREMENTS

Prevalence of diagnosed atopic dermatitis or eczema; proportions of respondents able to recall a past diagnosis of atopic dermatitis, eczema, or recurrent rash.

RESULTS

The prevalence of atopic dermatitis or eczema diagnosis in 2000 or 2001 was 0.8%. At least 2.4% of the cohort would be ineligible for smallpox vaccination because of active skin disease in themselves or household members. Among 94 adult respondents with atopic dermatitis, 55 (59%) correctly self-reported skin disease. Seventy-nine (60%) of 133 household contacts of adults with atopic dermatitis correctly reported the presence of skin disease in a household member. Parental recall of skin disease in children with atopic dermatitis was 70% (123 of 177).

CONCLUSIONS

Identifying dermatologic contraindications to smallpox vaccination by relying only on a self-reported history of rash illnesses is likely to miss a substantial proportion of individuals who should not receive smallpox vaccine in a preexposure vaccination campaign.

Vaccinations and risk of central nervous system demyelinating diseases in adults

BACKGROUND

Several case reports of the onset or exacerbation of multiple sclerosis or other demyelinating conditions shortly after vaccination have suggested that vaccines may increase the risk of demyelinating diseases.

OBJECTIVE

To evaluate the association between vaccination and onset of multiple sclerosis or optic neuritis.

DESIGN

Case-control study involving cases of multiple sclerosis or optic neuritis among adults 18 to 49 years of age. Data on vaccinations and other risk factors were obtained from computerized and paper medical records and from telephone interviews.

SETTING

Three health maintenance organizations.

PARTICIPANTS

Four hundred forty case subjects and 950 control subjects matched on health maintenance organization, sex, and date of birth.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Onset of first symptoms of demyelinating disease at any time after vaccination and during specified intervals after vaccination (<1 year, 1-5 years, and >5 years).

RESULTS

Cases and controls had similar vaccination histories. The odds ratios (95% confidence intervals), adjusted for potential confounding variables, of the associations between ever having been vaccinated and risk of demyelinating disease (multiple sclerosis and optic neuritis combined) were 0.9 (0.6-1.5) for hepatitis B vaccine; 0.6 (0.4-0.8) for tetanus vaccination; 0.8 (0.6-1.2) for influenza vaccine; 0.8 (0.5-1.5) for measles, mumps, rubella vaccine; 0.9 (0.5-1.4) for measles vaccine; and 0.7 (0.4-1.0) for rubella vaccine. The results were similar when multiple sclerosis and optic neuritis were analyzed separately. There was no increased risk according to timing of vaccination.

CONCLUSION

Vaccination against hepatitis B, influenza, tetanus, measles, or rubella is not associated with an increased risk of multiple sclerosis or optic neuritis.

Vaccine safety surveillance using large linked databases: opportunities, hazards and proposed guidelines

Combined administrative databases are referred to as 'large linked databases' because of their relatively large size and the need for linkage of different data sets that were created separately from each other. Such linked databases have become popular in vaccine safety surveillance. Whereas their use offers some unique opportunities, their increasingly widespread use can also lead to wrongful linkage of vaccines to adverse events. We review the opportunities and hazards of using large linked databases for vaccine safety surveillance and propose some guidelines to increase the reliability of the outcomes. We also offer our opinion on the future use of large linked databases for vaccine safety surveillance purposes.

Polio extraimmunization in children younger than 2 years after changes in immunization recommendations

OBJECTIVE

To investigate trends over time in polio extraimmunization among children in 4 large health maintenance organizations and to study the association with recent changes in polio immunization policy.

METHODS

Using 176 169 children who were born after 1994 and enrolled for their first 2 years of life, we assessed rates and trends of polio extraimmunization in the Vaccine Safety Datalink project. We used logistic regression to test the association of extraimmunization with different polio immunization schedules and with sociodemographic characteristics and used Poisson regression to test changes in rates over time.

RESULTS

Overall, 10.5% were extraimmunized for poliovirus; children on the all inactivated polio virus or sequential schedule were one half as likely as those on the all oral polio virus schedule to be extraimmunized by 2 years of age. There was a significant decrease in extraimmunization over time, with <5% of children born at the end of 1997 being extraimmunized, compared with >15% at the beginning of 1994.

CONCLUSIONS

Poliovirus extraimmunization rates have fallen dramatically in association with the change-over to the all inactivated polio virus schedule.

Surveillance for safety after immunization: Vaccine Adverse Event Reporting System (VAERS)--United States, 1991-2001

PROBLEM/CONDITION

Vaccines are usually administered to healthy persons who have substantial expectations for the safety of the vaccines. Adverse events after vaccinations occur but are generally rare. Some adverse events are unlikely to be detected in prelicensure clinical trials because of their low frequency, the limited numbers of enrolled subjects, and other study limitations. Therefore, postmarketing monitoring of adverse events after vaccinations is essential. The cornerstone of monitoring safety is review and analysis of spontaneously reported adverse events.

REPORTING PERIOD COVERED

This report summarizes the adverse events reported to the Vaccine Adverse Event Reporting System (VAERS) from January 1, 1991, through December 31, 2001.

DESCRIPTION OF SYSTEMS

VAERS was established in 1990 under the joint administration of CDC and the Food and Drug Administration (FDA) to accept reports of suspected adverse events after administration of any vaccine licensed in the United States. VAERS is a passive surveillance system: reports of events are voluntarily submitted by those who experience them, their caregivers, or others. Passive surveillance systems (e.g., VAERS) are subject to multiple limitations, including underreporting, reporting of temporal associations or unconfirmed diagnoses, and lack of denominator data and unbiased comparison groups. Because of these limitations, determining causal associations between vaccines and adverse events from VAERS reports is usually not possible. Vaccine safety concerns identified through adverse event monitoring nearly always require confirmation using an epidemiologic or other (e.g., laboratory) study. Reports may be submitted by anyone suspecting that an adverse event might have been caused by vaccination and are usually submitted by mail or fax. A web-based electronic reporting system has recently become available. Information from the reports is entered into the VAERS database, and new reports are analyzed weekly. VAERS data stripped of personal identifiers can be reviewed by the public by accessing http://www.vaers.org. The objectives of VAERS are to 1) detect new, unusual, or rare vaccine adverse events; 2) monitor increases in known adverse events; 3) determine patient risk factors for particular types of adverse events; 4) identify vaccine lots with increased numbers or types of reported adverse events; and 5) assess the safety of newly licensed vaccines.

RESULTS

During 1991-2001, VAERS received 128,717 reports, whereas >1.9 billion net doses of human vaccines were distributed. The overall dose-based reporting rate for the 27 frequently reported vaccine types was 11.4 reports per 100,000 net doses distributed. The proportions of reports in the age groups <1 year, 1-6 years, 7-17 years, 18-64 years, and >/= years were 18.1%, 26.7%, 8.0%, 32.6%, and 4.9%, respectively. In all of the adult age groups, a predominance among the number of women reporting was observed, but the difference in sex was minimal among children. Overall, the most commonly reported adverse event was fever, which appeared in 25.8% of all reports, followed by injection-site hypersensitivity (15.8%), rash (unspecified) (11.0%), injection-site edema (10.8%), and vasodilatation (10.8%). A total of 14.2% of all reports described serious adverse events, which by regulatory definition include death, life-threatening illness, hospitalization or prolongation of hospitalization, or permanent disability. Examples of the uses of VAERS data for vaccine safety surveillance are included in this report.

INTERPRETATION

As a national public health surveillance system, VAERS is a key component in ensuring the safety of vaccines. VAERS data are used by CDC, FDA, and other organizations to monitor and study vaccine safety. CDC and FDA use VAERS data to respond to public inquiries regarding vaccine safety, and both organizations have published and presented vaccine safety studies based on VAERS data. VAERS data are also used by the Advisory Committee on Immunization Practices and the Vaccine and Related Biological Products Advisory Committee to evaluate possible adverse events after vaccinations and to develop recommendations for precautions and contraindications to vaccinations. Reviews of VAERS reports and the studies based on VAERS reports during 1991-2001 have demonstrated that vaccines are usually safe and that serious adverse events occur but are rare.

PUBLIC HEALTH ACTIONS

Through continued reporting of adverse events after vaccination to VAERS by health-care providers, public health professionals, and the public and monitoring of reported events by the VAERS working group, the public health system will continue to be able to detect rare but potentially serious consequences of vaccination. This knowledge facilitates improvement in the safety of vaccines and the vaccination process.

Hepatitis B vaccine and risk of multiple sclerosis

The possibility that hepatitis B vaccine may cause or exacerbate multiple sclerosis stems from several case reports of onset or recurrence of symptoms of CNS demyelination shortly following vaccination. It is difficult, however, to infer causation from individual case reports since they may simply represent coincidental temporal associations with vaccination. There is only weak, nonspecific evidence to support the biological plausibility of an association between hepatitis B vaccine and multiple sclerosis. Epidemiological studies have found that hepatitis B vaccine does not increase the risk of developing multiple sclerosis or cause exacerbations. The US Institute of Medicine and other review panels have concluded that the evidence favors rejection of a causal association between hepatitis B vaccine and multiple sclerosis.