Predictive value of seizure ICD-9 codes for vaccine safety research

Neurological and immunological adverse events after pneumococcal conjugate vaccine in children using national immunization programme registry data

BACKGROUND

Despite the general consensus on the safety of pneumococcal conjugate vaccine (PCV), safety concerns unveiled during post-licensure surveillance need to be addressed. We investigated whether there is a transient increased risk following a three-dose series of pneumococcal conjugate vaccine (PCV) administered at 2, 4 and 6 months of age.

METHODS

This was a population-based cohort study using the Korea immunization registry data linked to nationwide administrative claims data. Self-controlled risk interval analysis was conducted for PCV recipients who had an outcome of interest within pre-defined risk and control intervals between 2018 and 2022. The outcomes were anaphylaxis, asthma, encephalopathy, febrile seizure, Kawasaki disease and thrombocytopenia. We used conditional Poisson regression model to estimate the incidence rate ratios (IRRs) and 95% confidence intervals (CIs) comparing the outcomes in the risk and control intervals.

RESULTS

Of 1 114 096 PCV recipients, 8661 had outcomes either in the risk or control intervals. Their mean age at Dose 1 was 10.0 weeks, 58.3% were boys, and 85.3% received 13-valent PCV. PCV was not associated with an increased risk of any outcomes except for febrile seizure. There were 408 (56.0%) cases of febrile seizure in the risk interval, corresponding to an IRR of 1.27 (95% CI 1.10-1.47).

CONCLUSIONS

It is reassuring to note that there was no increased risk of the potential safety concerns following PCV administration. Despite the transient increased risk of febrile seizure, absolute numbers of cases were small. Febrile seizure is generally self-limiting with a good prognosis, and should not discourage parents or caregivers from vaccinating their children.

Variability in Resource Utilization in the Evaluation and Management of Simple Febrile Seizures Inpatients in US Children's Hospitals

OBJECTIVE

To characterize resource utilization in the evaluation and treatment of hospitalized simple febrile seizure (SFS) patients in US tertiary pediatric hospitals.

METHODS

This is a retrospective cohort study using the Pediatric Health Information System from 2010 to 2015. Children 6 months to 5 years of age who were inpatients with a diagnosis of SFS. Children who had brain magnetic resonance imaging (MRI), electroencephalography (EEG), or received anticonvulsants were compared with those who did not have testing or anticonvulsant treatment. Hospital-level variation in the utilization rates of MRI, EEG, or treatment with anticonvulsants was also evaluated.

RESULTS

In Pediatric Health Information System-participating institutions, 8.4% (n=3640) of children presenting to the emergency department with SFS were hospitalized. Among these SFS inpatients, 57.8% (n= 2104) did not receive further evaluation with MRI/EEG or treatment with anticonvulsants. There was evidence of wide inter-hospital variation in resource utilization rates. The median (interquartile range) utilization rate was 6.2% (3.0 to 11.0%) for MRI, 28.5% (16.0 to 46.3%) for EEG and 17.1% (10.9 to 22.3%) for treatment with anticonvulsants.

CONCLUSION

No specific hospital-level factors were identified that contributed to the variation in resource utilization in the evaluation and management of hospitalized SFS patients.

Determining Which of Several Simultaneously Administered Vaccines Increase Risk of an Adverse Event

INTRODUCTION

Childhood immunization schedules often involve multiple vaccinations per visit. When increased risk of an adverse event is observed after simultaneous (same-day) vaccinations, it can be difficult to ascertain which triggered the adverse event. This methods paper discusses a systematic process to determine which of the simultaneously administered vaccine(s) are most likely to have caused an observed increase in risk of an adverse event.

METHODS

We use an example from the literature where excess risk of seizure was observed 1 day after vaccination, but same-day vaccination patterns made it difficult to discern which vaccine(s) may trigger the adverse event. We illustrate the systematic identification process using a simulation that retained the observed pattern of simultaneous vaccination in an empirical cohort of vaccinated children. We simulated "true" effects for diphtheria-tetanus-acellular pertussis (DTaP) and pneumococcal conjugate (PCV) on risk of seizure the day after vaccination. We varied the independent and interactive effects of vaccines (on the multiplicative scale). After applying the process to simulated data, we evaluated risk of seizure 1 day after vaccination in the empirical cohort.

RESULTS

In all simulations, we were able to determine which vaccines contributed to excess risk. In the empirical data, we narrowed the association with seizure from all vaccines in the schedule to three likely candidates, DTaP, PCV, and/or Haemophilus influenzae type B (HiB) (p < 0.01, attributable risk when all three were administered together: five per 100,000). Disentangling their associations with seizure would require a larger sample or more variation in the combinations administered. When none of these three were administered, no excess risk was observed.

CONCLUSION

The process outlined could provide valuable information on the magnitude of potential risk from individual and simultaneousvaccinations. Associations should be further investigated with independent data as well as biologically based, statistically independent hypotheses.

Use of Neuroimaging for Children With Seizure in General and Pediatric Emergency Departments

BACKGROUND

Seizure is a common reason for children to visit the emergency department (ED). Pediatric and general EDs may obtain computed tomography (CT) scans of the head for seizure at different rates.

OBJECTIVE

To compare rates of head CT for pediatric seizure between general and pediatric EDs.

METHODS

This was a retrospective cohort study using the National Hospital Ambulatory Medical Care Survey for patients <21 years of age presenting to an ED with a chief complaint or diagnosis of seizure between 2006 to 2017. Of these patients, we compared head CT use between general and pediatric EDs among patients with fever, trauma, and co-diagnosis of epilepsy using univariable risk differences and in a multivariable logistic regression model.

RESULTS

More than 5 (5.4) million (78.8%) and 1.5 million (21.2%) pediatric patients with seizure presented to general and pediatric EDs, respectively. Of those, 22.4% (1.21 million) and 13.2% (192,357) underwent CT scans of the head, respectively, a risk difference of 9.2% (95% confidence interval [CI] 2.3-16.1). General EDs obtained CT scans of the head more often in patients with epilepsy (risk difference 17.9% [95% CI 4.0-31.9]), without fever (12.2% [95% CI 3.1-21.4]), and without trauma (10.6% [95% CI 4.4-16.8]). Presenting to a general ED, being afebrile, or having trauma were associated with head CT with adjusted odds ratios of 1.7 (95% CI 1.0-3.2), 4.9 (95% CI 2.6-9.2), and 2.0 (95% CI 1.2-3.4), respectively. Age, gender, and epilepsy were not associated with head CT among all patients with seizure.

CONCLUSIONS

Children with seizure are more likely to undergo CT scans of the head at general EDs compared with pediatric EDs.

Rotavirus Vaccination Is Associated With Reduced Seizure Hospitalization Risk Among Commercially Insured US Children

Rotavirus commonly causes diarrhea but can also cause seizures. Analysis of insurance claims for 1773295 US children with 2950 recorded seizures found that, compared to rotavirus-unvaccinated children, seizure hospitalization risk was reduced by 24% (95% confidence interval [CI], 13%-33%) and 14% (95% CI, 0%-26%) among fully and partially rotavirus-vaccinated children, respectively.

The risk of varenicline-induced seizure among those who have attempted to quit smoking using pharmacotherapy

OBJECTIVE

Varenicline is an effective smoking cessation agent; however, its use is limited because of black box warnings issued by regulatory agencies in the U.S. and Australia. The U.S. Food and Drug Administration updated the label for varenicline in 2015 to warn about the risk of varenicline-induced seizures. The objective of this study was to examine the risk of seizure associated with varenicline use.

METHODS

A nested case-control study was performed using IMS LifeLink PharMetrics Plus administrative claims data (2009-2015). The outcome was presumptive seizures. All smokers making an attempt to quit smoking and having no recent seizure events were included in the nest. Cases and controls were matched (1:4) on age (±5 years), sex, index date (±30 days), event date, and duration of enrollment. An exposure period of 90 days preceding the event date was used. Chi-square tests were used to compare the characteristics of cases and controls. Conditional logistic regression was conducted to determine if an association between presumptive seizures and varenicline use exists.

RESULTS

Our final sample was comprised of 1342 cases and 5368 controls. The adjusted analysis showed that odds of a seizure for patients with a varenicline prescription were 1.09 (confidence interval [CI] = 0.88-1.36) times those of patients with no varenicline exposure.

CONCLUSIONS

This study did not find a significant association between varenicline and increased risk of presumptive seizures. These findings raise questions regarding the necessity for a warning label for increased risk of seizures associated with varenicline.

Challenges and Opportunities for Using Big Health Care Data to Advance Medical Science and Public Health

Methodological advancements in epidemiology, biostatistics, and data science have strengthened the research world's ability to use data captured from electronic health records (EHRs) to address pressing medical questions, but gaps remain. We describe methods investments that are needed to curate EHR data toward research quality and to integrate complementary data sources when EHR data alone are insufficient for research goals. We highlight new methods and directions for improving the integrity of medical evidence generated from pragmatic trials, observational studies, and predictive modeling. We also discuss needed methods contributions to further ease data sharing across multisite EHR data networks. Throughout, we identify opportunities for training and for bolstering collaboration among subject matter experts, methodologists, practicing clinicians, and health system leaders to help ensure that methods problems are identified and resulting advances are translated into mainstream research practice more quickly.

Epidemiology and Resource Utilization of Simple Febrile Seizure-associated Hospitalizations in the United States, 2003-2012

BACKGROUND

Simple febrile seizure (SFS) affects 2% to 4% of children under 6 years of age. The purpose of this study is to examine the epidemiologic patterns and resource utilization of SFS-associated hospitalizations in children aged younger than 6 years of age in the United States.

MATERIALS AND METHODS

This study is a serial, retrospective analysis of the Healthcare Cost and Utilization Project Kids' Inpatient Databases for the years 2003, 2006, 2009, and 2012. SFS-associated hospitalizations were identified based on International Classification of Diseases, Ninth Revision, Clinical Modification, diagnosis code 780.31. We calculated the proportion of hospitalizations in pediatric patients under 6 years of age due to SFS and all other nonbirth causes, the rate of SFS-associated hospitalizations per 100,000 population, the mean length of stay and inflation-adjusted hospital costs of SFS-associated hospitalizations, as well as patient demographics and hospital characteristics.

RESULTS

From 2003 to 2012, the weighted proportion of hospitalizations due to SFS declined from 0.83% to 0.41% (P<0.01) and the annual rate of SFS-associated hospitalizations per 100,000 population decreased from 48.0 to 18.7 (P<0.01). However, use of computed tomography, electroencephalogram, and lumbar puncture in SFS-associated hospitalizations decreased significantly (all P<0.001), but the utilization rate of magnetic resonance imaging remained stable (P=0.53). The mean length of stay for SFS-associated hospitalizations decreased from 2.03 days in 2003 to 1.74 days in 2012, and the mean hospital costs (exclusive of professional payment) decreased from $3830 in 2003 to $3223 in 2012 (both P<0.001).

CONCLUSIONS

SFS-associated hospitalizations and resource utilization in children under 6 years of age have decreased markedly in the United States, probably due to improved clinical adherence to the practice parameters set forth by the American Academy of Pediatrics for managing patients with SFS.

Readmission after seizure discharge in a nationally representative sample

OBJECTIVE

To determine the 30-day readmission rate after seizure-related discharge in a nationally representative sample, as well as patient, clinical, and hospital characteristics associated with readmission.

METHODS

Retrospective cohort study of adults discharged alive from a nonelective hospitalization for epilepsy or seizure, sampled from the Healthcare Cost and Utilization Project's 2014 Nationwide Readmissions Database. Descriptive statistics and logistic regression models were built to quantify and characterize nonelective readmission within 30 days.

RESULTS

A total of 139,800 admissions met inclusion criteria, of which 15,094 (10.8%) were readmitted within 30 days. Patient characteristics associated with readmission included comorbid disease burden (Elixhauser score 2: adjusted odds ratio [AOR] [95% confidence interval (CI)] 1.38 [1.21-1.57]; Elixhauser score 3: AOR 1.52 [1.34-1.73]; Elixhauser score >4: AOR 2.28 [2.01-2.58] as compared to 1) and participation in public insurance programs (Medicare: AOR 1.39 [1.26-1.54]; Medicaid: AOR 1.39 [1.26-1.54] as compared to private insurance). Adverse events (AOR 1.17 [1.05-1.30]) and prolonged length of stay, as well as nonroutine discharge (AOR 1.32 [1.23-1.42]), were also associated with increased adjusted odds of readmission. The most common primary reason for readmission was epilepsy or convulsion (17%).

CONCLUSIONS

Patients hospitalized with seizure are frequently readmitted. While readmitted patients are more likely to have multiple medical comorbidities, our study demonstrated that inpatient adverse events were also significantly associated with readmission. The most common reason for readmission was seizure or epilepsy. Together, these 2 findings suggest that a proportion of readmissions are related to modifiable care process factors and may therefore be avoidable. Further study into understanding preventable drivers of readmission in this population presents an opportunity to improve patient outcomes and health.

Similar relative risks of seizures following measles containing vaccination in children born preterm compared to full-term without previous seizures or seizure-related disorders

BACKGROUND

Febrile seizures are associated with the first dose of measles-containing vaccines and the risk increases with chronologic age during the second year of life. We used the Vaccine Safety Datalink (VSD) to determine if the relative increase in risk of seizures following receipt of measles-containing vaccine differs by gestational age at birth.

METHODS

Children were eligible if they received their first dose of measles-containing vaccine at age 12 through 23 months from January 2003 through September 2015. Children were excluded if they had a history of seizure or conditions strongly related to seizure prior to 12 months of age. Seizures were identified by diagnostic codes in the inpatient or emergency department settings. Using risk-interval analysis, we estimated the incidence rate ratio (IRR) for seizures in the 7 through 10 days (risk period) vs 15 through 42 days (control period) following receipt of measles-containing vaccines in children born preterm (<37 weeks gestation age) and those born full-term (≥37 weeks).

RESULTS

There were 532,375 children (45,343 preterm and 487,032 full-term) who received their first dose of measles-containing vaccine at age 12 through 23 months. The IRRs of febrile seizures 7 through 10 days compared with 15 through 42 days after receipt of measles-containing vaccine were 3.9 (95% CI: 2.5-6.0) in preterm children and 3.2 (2.7-3.7) in full-term children; the ratio of IRRs: was 1.2 (0.76-1.9), p = 0.41. IRRs were also similar across gestational age groups, by vaccine type received (measles-mumps-rubella [MMR] or measles-mumps-rubella-varicella [MMRV]) and age at vaccination (12-15 or 16-23 months).

CONCLUSION

Vaccination with a measles-containing vaccine in the second year of life is associated with a similar relative risk of a first seizure in children born preterm as in those who were born full-term.

Bias from outcome misclassification in immunization schedule safety research

PURPOSE

The Institute of Medicine recommended conducting observational studies of childhood immunization schedule safety. Such studies could be biased by outcome misclassification, leading to incorrect inferences. Using simulations, we evaluated (1) outcome positive predictive values (PPVs) as indicators of bias of an exposure-outcome association, and (2) quantitative bias analyses (QBA) for bias correction.

METHODS

Simulations were conducted based on proposed or ongoing Vaccine Safety Datalink studies. We simulated 4 studies of 2 exposure groups (children with no vaccines or on alternative schedules) and 2 baseline outcome levels (100 and 1000/100 000 person-years), with 3 relative risk (RR) levels (RR = 0.50, 1.00, and 2.00), across 1000 replications using probabilistic modeling. We quantified bias from non-differential and differential outcome misclassification, based on levels previously measured in database research (sensitivity > 95%; specificity > 99%). We calculated median outcome PPVs, median observed RRs, Type 1 error, and bias-corrected RRs following QBA.

RESULTS

We observed PPVs from 34% to 98%. With non-differential misclassification and true RR = 2.00, median bias was toward the null, with severe bias (median observed RR = 1.33) with PPV = 34% and modest bias (median observed RR = 1.83) with PPV = 83%. With differential misclassification, PPVs did not reflect median bias, and there was Type 1 error of 100% with PPV = 90%. QBA was generally effective in correcting misclassification bias.

CONCLUSIONS

In immunization schedule studies, outcome misclassification may be non-differential or differential to exposure. Overall outcome PPVs do not reflect the distribution of false positives by exposure and are poor indicators of bias in individual studies. Our results support QBA for immunization schedule safety research.

The safety of live attenuated influenza vaccine in children and adolescents 2 through 17 years of age: A Vaccine Safety Datalink study

PURPOSE

To evaluate the safety of live attenuated influenza vaccine (LAIV) in children 2 through 17 years of age.

METHODS

The study was conducted in 6 large integrated health care organizations participating in the Vaccine Safety Datalink (VSD). Trivalent LAIV safety was assessed in children who received LAIV between September 1, 2003 and March 31, 2013. Eighteen pre-specified adverse event groups were studied, including allergic, autoimmune, neurologic, respiratory, and infectious conditions. Incident rate ratios (IRRs) were calculated for each adverse event, using self-controlled case series analyses. For adverse events with a statistically significant increase in risk, or an IRR > 2.0 regardless of statistical significance, manual medical record review was performed to confirm case status.

RESULTS

During the study period, 396 173 children received 590 018 doses of LAIV. For 13 adverse event groups, there was no significant increased risk of adverse events following LAIV. Five adverse event groups (anaphylaxis, syncope, Stevens-Johnson syndrome, adverse effect of drug, and respiratory failure) met criteria for manual medical record review. After review to confirm cases, 2 adverse event groups remained significantly associated with LAIV: anaphylaxis and syncope. One confirmed case of anaphylaxis was observed following LAIV, a rate of 1.7 per million LAIV doses. Five confirmed cases of syncope were observed, a rate of 8.5 per million doses.

CONCLUSIONS

In a study of trivalent LAIV safety in a large cohort of children, few serious adverse events were detected. Anaphylaxis and syncope occurred following LAIV, although rarely. These data provide reassurance regarding continued LAIV use.

Febrile Seizure Risk after Vaccination in Children One to Five Months of Age

BACKGROUND

The risk of febrile seizure is temporarily increased for a few days after the administration of certain vaccines in children aged six to 23 months. Our objective was to determine the febrile seizure risk following vaccination in children aged one to five months, when six different vaccines are typically administered.

METHODS

We identified emergency department visits and inpatient admissions with International Classification of Diseases, Ninth Revision, febrile seizure codes among children enrolled in nine Vaccine Safety Datalink participating health care organizations from 2006 through 2011. Febrile seizures were confirmed by medical record abstraction. We used the self-controlled risk-interval method to compare the incidence of febrile seizure during postvaccination days 0 to 1 (risk interval) versus days 14 to 20 (control interval).

RESULTS

We identified 15 febrile seizure cases that occurred after 585,342 vaccination visits. The case patients were aged three to five months. The patients had received a median of four (range two to six) vaccines simultaneously. The incidence rate ratio of febrile seizure after vaccination was 23 (95% confidence interval 5.13 to 100.8), and the attributable risk was 3.92 (95% confidence interval 1.68 to 6.17) febrile seizure cases per 100,000 persons vaccinated.

CONCLUSIONS

Vaccination in children aged three to five months was associated with a large relative risk of febrile seizure on the day of and the day after vaccination, but the risk was small in absolute terms. Postvaccination febrile seizure should not be a concern for the vast majority of children receiving vaccines, but clinicians might take this risk into consideration when evaluating and treating children susceptible to seizures precipitated by fever.

Post licensure surveillance of influenza vaccines in the Vaccine Safety Datalink in the 2013-2014 and 2014-2015 seasons

PURPOSE

The changes in each year in influenza vaccine antigenic components as well as vaccine administration patterns may pose new risks of adverse events following immunization (AEs). To evaluate the safety of influenza vaccines annually administered to people ≥ 6 months, we conducted weekly post licensure surveillance for seven pre-specified adverse events following receipt of influenza vaccines during the 2013-2014 and 2014-2015 seasons in the Vaccine Safety Datalink (VSD).

METHODS

We used both a historically-controlled cohort design with the Poisson-based maximized sequential probability ratio test (maxSPRT) and a self-controlled risk interval (SCRI) design with the binomial-based maxSPRT. For each adverse event outcome, we defined the risk interval on the basis of biologic plausibility and prior literature. For the historical cohort design, numbers of expected adverse events were calculated from the prior seven seasons, adjusted for age and site. For the SCRI design, a comparison window was defined either before vaccination or after vaccination, depending on each specific outcome.

RESULTS

An elevated risk of febrile seizures 0-1 days following trivalent inactivated influenza vaccine (IIV3) was identified in children aged 6-23 months during the 2014-2015 season using the SCRI design. We found the relative risk (RR) of febrile seizures following concomitant administration of IIV3 and PCV13 was 5.3 with a 95% CI 1.87-14.75. Without concomitant PCV 13 administration, the estimated risk decreased and was no longer statistically significant (RR: 1.4; CI: 0.54 - 3.61).

CONCLUSION

No increased risks, other than for febrile seizures, were identified in influenza vaccine safety surveillance during 2013-2014 and 2014-2015 seasons in the VSD. Copyright © 2016 John Wiley & Sons, Ltd.

Febrile Seizure Risk After Vaccination in Children 6 to 23 Months

BACKGROUND AND OBJECTIVE

An increased risk of febrile seizure (FS) was identified with concomitant administration of trivalent inactivated influenza vaccine (IIV3) and pneumococcal conjugate vaccine (PCV) 13-valent during the 2010-2011 influenza season. Our objective was to determine whether concomitant administration of IIV3 with other vaccines affects the FS risk.

METHODS

We examined the risk of FS 0 to 1 day postvaccination for all routinely recommended vaccines among children aged 6 through 23 months during a period encompassing 5 influenza seasons (2006-2007 through 2010-2011). We used a population-based self-controlled risk interval analysis with a control interval of 14 to 20 days postvaccination. We used multivariable regression to control for receipt of concomitant vaccines and test for interaction between vaccines.

RESULTS

Only PCV 7-valent had an independent FS risk (incidence rate ratio [IRR], 1.98; 95% confidence interval [CI], 1.00 to 3.91). IIV3 had no independent risk (IRR, 0.46; 95% CI, 0.21 to 1.02), but risk was increased when IIV3 was given with either PCV (IRR, 3.50; 95% CI, 1.13 to 10.85) or a diphtheria-tetanus-acellular-pertussis (DTaP)-containing vaccine (IRR, 3.50; 95% CI, 1.52 to 8.07). The maximum estimated absolute excess risk due to concomitant administration of IIV3, PCV, and DTaP-containing vaccines compared with administration on separate days was 30 FS per 100 000 persons vaccinated.

CONCLUSIONS

The administration of IIV3 on the same day as either PCV or a DTaP-containing vaccine was associated with a greater risk of FS than when IIV3 was given on a separate day. The absolute risk of postvaccination FS with these vaccine combinations was small.

Unmasking in an observational vaccine safety study: Using type 2 diabetes mellitus as an example

BACKGROUND

In observational vaccine safety studies, diagnosis codes assigned prior to or on the day of vaccination (Day 0) are often excluded from analysis of safety signals since they usually represent pre-existing conditions. The limitations of this approach have been described for autoimmune conditions but not for other chronic conditions. We draw on our experience in a post-licensure quadrivalent human papillomavirus vaccine (HPV4) safety study to examine the effectiveness of exclusion of pre-existing and Day 0 diagnoses of type 2 diabetes mellitus (T2DM) in excluding prevalent T2DM.

METHODS

Subjects included all 117,402 females ages 9-26 years who received HPV4 August 2006-March 2008 in Kaiser Permanente Southern California. We identified potential incident T2DM cases using ICD9 code 250.xx associated with inpatient and emergency room visits during the 60 days following each HPV4 dose, excluding those with this code prior to their first HPV4 dose. Electronic medical records were reviewed to determine the dates of symptom onset, diagnostic labs, vaccine administration and T2DM diagnosis.

RESULTS

Of 33 potential incident T2DM cases identified using automated data, 4 (12%) were confirmed to have new onset T2DM after medical record review. Nineteen cases were excluded that did not have T2DM or had T2DM diagnosed before Day 0; nine had an abnormal fasting blood sugar (FBS) ordered on Day 0, prompting subsequent evaluation and diagnosis of T2DM; and one had elevated FBS and glucosuria prior to the first dose of HPV4 but T2DM diagnosed at a visit following vaccination.

CONCLUSION

These results suggest that among adolescents and young adults, the workup and subsequent diagnosis of pre-existing conditions may result from a visit at which a vaccination is administered. This "unmasking" phenomenon is not entirely eliminated by exclusion of pre-existing and Day 0 diagnoses. Medical record review should be considered in the evaluation of potential safety signals.

Febrile Seizures After 2010-2011 Trivalent Inactivated Influenza Vaccine

OBJECTIVES

In the Post-Licensure Rapid Immunization Safety Monitoring Program, we examined risk of febrile seizures (FS) after trivalent inactivated influenza vaccine (TIV) and 13-valent pneumococcal conjugate vaccine (PCV13) during the 2010-2011 influenza season, adjusted for concomitant diphtheria tetanus acellular pertussis-containing vaccines (DTaP). Assuming children would receive both vaccines, we examined whether same-day TIV and PCV13 vaccination was associated with greater FS risk when compared with separate-day vaccination.

METHODS

We used a self-controlled risk interval design, comparing the FS rate in a risk interval (0-1 days) versus control interval (14-20 days). Vaccinations were identified in claims and immunization registry data. FS were confirmed with medical records.

RESULTS

No statistically significant TIV-FS associations were found in unadjusted or adjusted models (incidence rate ratio [IRR] adjusted for age, seasonality, and concomitant PCV13 and DTaP: 1.36, 95% confidence interval [CI] 0.78 to 2.39). Adjusted for age and seasonality, PCV13 was significantly associated with FS (IRR 1.74, 95% CI 1.06 to 2.86), but not when further adjusting for concomitant TIV and DTaP (IRR 1.61, 95% CI 0.91 to 2.82). Same-day TIV and PCV13 vaccination was not associated with excess risk of FS when compared with separate-day vaccination (1.08 fewer FS per 100 000 with same day administration, 95% CI -5.68 to 6.09).

CONCLUSIONS

No statistically significant increased risk of FS was found for 2010-2011 TIV or PCV13, when adjusting for concomitant vaccines. Same-day TIV and PCV13 vaccination was not associated with more FS compared with separate-day vaccination.

Impact of Rotavirus Vaccination on Childhood Hospitalization for Seizures

BACKGROUND

Rotavirus vaccine (RV) might reduce the risk of hospitalization due to childhood seizures (CS). We aimed to identify and assess variations in the incidence of hospitalizations for CS among children <5 years of age before and after RV introduction.

METHODS

Annual hospitalization rates for any kind of CS, before and after RV introduction in 2007, were calculated using the official surveillance system for hospitalization data.

RESULTS

Our study cohort totaled 6149 children <5 years of age admitted to the hospital between 2003 and 2013 with any kind of CS (780.3* + 779.0* + 333.2* + 345* ICD-9-CM code). The annual hospitalization rates for any kind of CS in children <5 years of age were correlated with RV coverage (r = -0.673; P = 0.033) and rotavirus acute gastroenteritis admission rates (ρ = 0.506; P = 0.001), with decrease rates ranging from 16.2% (95% confidence interval: 8.3-23.5%) in 2007 to 34.0% (27.3-40.1%) in 2010, as compared with the median rate of the pre-vaccination period (2003 to 2006). Similarly, for convulsions (780.3*ICD-9-CM code), the decrease seen in children <5 years of age was significantly correlated with the increase in RV coverage (r = -0.747; P = 0.013) and rotavirus acute gastroenteritis admission rates (ρ = 0.543; P < 0.001), with decrease rates ranging from 18.7% (9.6-26.8%) in 2007 to 42.5% (35.3-48.9%) in 2012. Significant results were also obtained for infants <12 months and infants 1-2 years of age. In the remaining age groups or diagnostic categories analyzed, changes were either not significant or not related to vaccination changes or rotavirus acute gastroenteritis admission rates.

CONCLUSIONS

Our results show that rotavirus vaccination may have a significant impact in the decrease in seizure-related hospitalizations in childhood. This additional benefit of rotavirus vaccination seems more marked in the youngest infants.

Post-licensure rapid immunization safety monitoring program (PRISM) data characterization

BACKGROUND

The Post-Licensure Rapid Immunization Safety Monitoring (PRISM) program is the immunization safety monitoring component of FDA's Mini-Sentinel project, a program to actively monitor the safety of medical products using electronic health information. FDA sought to assess the surveillance capabilities of this large claims-based distributed database for vaccine safety surveillance by characterizing the underlying data.

METHODS

We characterized data available on vaccine exposures in PRISM, estimated how much additional data was gained by matching with select state and local immunization registries, and compared vaccination coverage estimates based on PRISM data with other available data sources. We generated rates of computerized codes representing potential health outcomes relevant to vaccine safety monitoring. Standardized algorithms including ICD-9 codes, number of codes required, exclusion criteria and location of the encounter were used to obtain the background rates.

RESULTS

The majority of the vaccines routinely administered to infants, children, adolescents and adults were well captured by claims data. Immunization registry data in up to seven states comprised between 5% and 9% of data for all vaccine categories with the exception of 10% for hepatitis B and 3% and 4% for rotavirus and zoster respectively. Vaccination coverage estimates based on PRISM's computerized data were similar to but lower than coverage estimates from the National Immunization Survey and Healthcare Effectiveness Data and Information Set. For the 25 health outcomes of interest studied, the rates of potential outcomes based on ICD-9 codes were generally higher than rates described in the literature, which are typically clinically confirmed cases.

CONCLUSION

PRISM program's data on vaccine exposures and health outcomes appear complete enough to support robust safety monitoring.

Timely versus delayed early childhood vaccination and seizures

BACKGROUND

Little is known regarding the timing of childhood vaccination and postvaccination seizures.

METHODS

In a cohort of 323 247 US children from the Vaccine Safety Datalink born from 2004 to 2008, we analyzed the association between the timing of childhood vaccination and the first occurrence of seizure with a self-controlled case series analysis of the first doses of individual vaccines received in the first 2 years of life.

RESULTS

In infants, there was no association between the timing of infant vaccination and postvaccination seizures. In the second year of life, the incident rate ratio (IRR) for seizures after receipt of the first measles-mumps-rubella vaccine (MMR) dose at 12 to 15 months was 2.65 (95% confidence interval [CI] 1.99-3.55); the IRR after an MMR dose at 16 to 23 months was 6.53 (95% CI 3.15-13.53). The IRR for seizures after receipt of the first measles-mumps-rubella-varicella vaccine (MMRV) dose at 12 to 15 months was 4.95 (95% CI 3.68-6.66); the IRR after an MMRV dose at 16 to 23 months was 9.80 (95% CI 4.35 -22.06).

CONCLUSIONS

There is no increased risk of postvaccination seizure in infants regardless of timing of vaccination. In year 2, delaying MMR vaccine past 15 months of age results in a higher risk of seizures. The strength of the association is doubled with MMRV vaccine. These findings suggest that on-time vaccination is as safe with regard to seizures as delayed vaccination in the first year of life, and that delayed vaccination in the second year of life is associated with more postvaccination seizures than on-time vaccination.

Safety of diphtheria, tetanus, acellular pertussis and inactivated poliovirus (DTaP-IPV) vaccine

BACKGROUND

In 2008, a diphtheria, tetanus, acellular pertussis, and inactivated poliovirus combined vaccine (DTaP-IPV) was licensed for use in children 4 through 6 years of age. While pre-licensure studies did not demonstrate significant safety concerns, the number vaccinated in these studies was not sufficient to examine the risk of uncommon but serious adverse events.

OBJECTIVE

To assess the risk of serious adverse events following DTaP-IPV vaccination.

METHODS

The study was conducted from January 2009 through September 2012 in the Vaccine Safety Datalink (VSD) project. In the VSD, electronic vaccination and encounter data are updated and aggregated weekly as part of ongoing surveillance activities. Based on previous reports and biologic plausibility, eight potential adverse events were monitored: meningitis/encephalitis; seizures; stroke; Guillain-Barré syndrome; Stevens-Johnson syndrome; anaphylaxis; serious allergic reactions other than anaphylaxis; and serious local reactions. Adverse event rates in DTaP-IPV recipients were compared to historical incidence rates in the VSD population prior to 2009. Sequential probability ratio testing was used to analyze the data on a weekly basis.

RESULTS

During the study period, 201,116 children received DTaP-IPV vaccine. Ninety-seven percent of DTaP-IPV recipients also received other vaccines on the same day, typically measles-mumps-rubella and varicella vaccines. There was no statistically significant increased risk of any of the eight pre-specified adverse events among DTaP-IPV recipients when compared to historical incidence rates.

CONCLUSIONS

In this safety surveillance study of more than 200,000 DTaP-IPV vaccine recipients, there was no evidence of increased risk for any of the pre-specified adverse events monitored. Continued surveillance of DTaP-IPV vaccine safety may be warranted to monitor for rare adverse events, such as Guillain-Barré syndrome.

Absence of associations between influenza vaccines and increased risks of seizures, Guillain-Barré syndrome, encephalitis, or anaphylaxis in the 2012-2013 season

PURPOSE

We conducted weekly surveillance for pre-specified adverse events following receipt of the 2012-2013 influenza vaccines in the Vaccine Safety Datalink (VSD).

METHODS

For each outcome, risk intervals (i.e., period after vaccination with a potentially increased risk) were defined on the basis of biologic plausibility and prior literature. Seizures following inactivated influenza vaccine (IIV) were monitored in children in three age groups (6-23 months, 24-59 months, and 5-17 years) using a self-controlled risk interval design. We also monitored for Guillain-Barré syndrome, encephalitis, and anaphylaxis following IIV in patients ≥6 months of age using a cohort design with historical controls. In the risk intervals following live attenuated influenza vaccine (LAIV), we collected weekly counts of Guillain-Barré syndrome, encephalitis, and anaphylaxis in patients ages 2-49. Among LAIV vaccinees, numbers of expected events based on rates in historical controls were calculated, adjusted for age and site.

RESULTS

At the end of surveillance, approximately 3.6 million first doses of IIV and 250 000 first doses of LAIV had been administered in the VSD. No elevated risks were identified in risk intervals following 2012-2013 IIV, as compared with a self-matched control interval or to historical controls. For each outcome, fewer than three events occurred in the risk interval following 2012-2013 LAIV, and we thus were unable to estimate measures of relative risks.

CONCLUSIONS

No increased risk was identified for any of the pre-specified outcomes following 2012-2013 influenza vaccinations in the VSD. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Epilepsy and vaccinations: Italian guidelines

Reports of childhood epilepsies in temporal association with vaccination have had a great impact on the acceptance of vaccination programs by health care providers, but little is known about this possible temporal association and about the types of seizures following vaccinations. For these reasons the Italian League Against Epilepsy (LICE), in collaboration with other Italian scientific societies, has decided to generate Guidelines on Vaccinations and Epilepsy. The aim of Guidelines on Vaccinations and Epilepsy is to present recent unequivocal evidence from published reports on the possible relationship between vaccines and epilepsy in order to provide information about contraindications and risks of vaccinations in patients with epilepsy. The following main issues have been addressed: (1) whether contraindications to vaccinations exist in patients with febrile convulsions, epilepsy, and/or epileptic encephalopathies; and (2) whether any vaccinations can cause febrile seizures, epilepsy, and/or epileptic encephalopathies. Diphtheria-tetanus-pertussis (DTP) vaccination and measles, mumps, and rubella vaccination (MMR) increase significantly the risk of febrile seizures. Recent observations and data about the relationships between vaccination and epileptic encephalopathy show that some cases of apparent vaccine-induced encephalopathy could in fact be caused by an inherent genetic defect with no causal relationship with vaccination.

Protective association between rotavirus vaccination and childhood seizures in the year following vaccination in US children

BACKGROUND

Rotavirus illness has been linked to childhood seizures. We investigated whether a protective association exists between receipt of rotavirus vaccine and being hospitalized or visiting the emergency department for seizures in the year after vaccination.

METHODS

We retrospectively analyzed a cohort of children born after 28 February 2006 (when rotavirus vaccine was licensed in the United States) and enrolled in the Vaccine Safety Datalink (VSD) through November 2009. Seizure rates from 4 to 55 weeks following last rotavirus vaccination were compared by vaccine exposure status (fully vaccinated and unvaccinated). A time-to-event analysis using a Cox proportional hazards model was performed, accounting for time-varying covariates. We calculated the relative incidence of seizure compared by vaccine exposure status during the postexposure interval.

RESULTS

Our cohort contained VSD data on 250 601 infants, including 186 502 children fully vaccinated (74.4%) and 64 099 (25.6%) not vaccinated with rotavirus vaccine. Rates of seizures were associated with rotavirus vaccination status. After adjusting for covariates (VSD site, age at last dose, sex, and calendar month of the index date), a statistically significant protective association was observed between a full course of rotavirus vaccination vs no vaccination for both first-ever seizures (risk ratio [RR] = 0.82; 95% confidence interval [CI], .73-.91) and all seizures (RR = 0.79; 95% CI, .71-.88).

CONCLUSIONS

A full course of rotavirus vaccination was statistically associated with an 18%-21% reduction in risk of seizure requiring hospitalization or emergency department care in the year following vaccination, compared with unvaccinated children. This reduction in childhood seizures complements the well-documented vaccine-related benefit of preventing US diarrhea hospitalizations.

Identification of seizures among adults and children following influenza vaccination using health insurance claims data

INTRODUCTION

Post-licensure surveillance of adverse events following vaccination or prescription drug use often relies on electronic healthcare data to efficiently detect and evaluate safety signals. The accuracy of seizure-related diagnosis codes in identifying true incident seizure events in vaccine safety studies is influenced by factors such as clinical setting of diagnosis and age. To date, most studies of post-vaccination seizure have focused on pediatric populations. More information is needed on how well seizure can be identified in adults and children using algorithms that rely on electronic healthcare data.

METHODS

This validation study was part of a larger safety study of influenza vaccination during the 2009-2010 and 2010-2011 influenza seasons. Children and adults receiving influenza vaccination were drawn from an administrative claims database of a large United States healthcare insurer. Potential seizure events were identified using an algorithm of ICD-9 diagnosis codes associated with an emergency department (ED) visit or hospitalization within pre-specified risk windows following influenza vaccination. Seizure events were confirmed through medical record review. The positive predictive value (PPV) of the algorithm was calculated within each diagnostic setting and stratified by age group, ICD-9 code group, and sex.

RESULTS

Review confirmed 113 out of 176 potential seizure events. The PPVs were higher in the ED setting (93.9%) than in the inpatient setting (38.3%). The PPVs by age varied within the ED setting (98.2% in <7 years, 76.9% in 7-24 years, 92.3% in ≥25 years) and within the inpatient setting (64.7% in <7 years, 33.3% in 7-24 years, 32.3% in ≥25 years).

CONCLUSIONS

Our algorithm for identification of seizure events using claims data had a high level of accuracy in the emergency department setting in young children and older adults and a lower, but acceptable, level of accuracy in older children and young adults.

Applicability of the Brighton Collaboration Case Definition for seizure after immunization in active and passive surveillance in Canada

BACKGROUND

The Canadian Adverse Event Following Immunization Surveillance System (CAEFISS) receives reports via active syndromic surveillance for selected serious AEFI from the Canadian Immunization Monitoring Program Active (IMPACT) and via targeted passive surveillance from Federal/Provincial/Territorial health jurisdictions. Post-immunization seizure is a target of active and passive surveillance. Since 2009, the revised national AEFI reporting forms enable capture of terms specific to several Brighton Collaboration Case Definitions (BCCD) including generalized seizure and fever.

OBJECTIVE

To evaluate feasibility of applying the BCCD for generalized seizure to adverse event following immunization (AEFI) reports collected by IMPACT and targeted passive surveillance (non-IMPACT).

METHODS

Reports to CAEFISS coded as seizure in children <2 years of age (vaccination dates 1998-2011) were reviewed retrospectively. A BCCD level (1-5 or unclassifiable) was assigned. The effects of reporting source (IMPACT versus non-IMPACT), seriousness [serious (e.g., hospitalized) versus non-serious], vaccination year (1998-2008 versus 2009-2011), and data submission method to CAEFISS (electronic versus paper) were assessed by stratified analysis.

RESULTS

There were 459 IMPACT and 908 non-IMPACT cases analyzed, of which 99.6% and 27%, respectively, were serious reports. The revised reporting form that captured the BCCD components (2009-2011) was associated with increased proportions of IMPACT and non-IMPACT cases meeting the BCCD for generalized seizure.

CONCLUSIONS

Incorporating the BCCD components (level of consciousness, motor manifestations and fever ≥38°C) into the national reporting form and guidelines appeared to improve the feasibility of their use in AEFI surveillance. This effect was more pronounced among active syndromic surveillance compared to targeted passive surveillance reports.

Signal identification and evaluation for risk of febrile seizures in children following trivalent inactivated influenza vaccine in the Vaccine Safety Datalink Project, 2010-2011

In fall 2010 in the southern hemisphere, an increased risk of febrile seizures was noted in young children in Australia in the 24 h after receipt of trivalent inactivated influenza vaccine (TIV) manufactured by CSL Biotherapies. Although the CSL TIV vaccine was not recommended for use in young children in the US, during the 2010-2011 influenza season near real-time surveillance was conducted for febrile seizures in the 0-1 days following first dose TIV in a cohort of 206,174 vaccinated children ages 6 through 59 months in the Vaccine Safety Datalink Project. On a weekly basis, surveillance was conducted with the primary approach of a self-controlled risk interval design and the secondary approach of a current vs. historical vaccinee design. Sequential statistical methods were employed to account for repeated analyses of accumulating data. Signals for seizures based on computerized data were identified in mid November 2010 using a current vs. historical design and in late December 2010 using a self-controlled risk interval design. Further signal evaluation was conducted with chart-confirmed febrile seizure cases using only data from the primary approach (i.e. self-controlled risk interval design). The magnitude of the incidence rate ratio and risk difference comparing risk of seizures in the 0-1 days vs. 14-20 days following TIV differed by receipt of concomitant 13-valent pneumococcal conjugate vaccine (PCV13). Among children 6-59 months of age, the incidence rate ratio (IRR) for TIV adjusted for concomitant PCV13 was 2.4 (95% CI 1.2, 4.7) while the IRR for PCV13 adjusted for concomitant TIV was 2.5 (95% CI 1.3, 4.7). The IRR for concomitant TIV and PCV13 was 5.9 (95% CI 3.1, 11.3). Risk difference estimates varied by age due to the varying baseline risk for seizures in young children, with the highest estimates occurring at 16 months (12.5 per 100,000 doses for TIV without concomitant PCV13, 13.7 per 100,000 doses for PCV13 without concomitant TIV, and 44.9 per 100,000 doses for concomitant TIV and PCV13) and the lowest estimates occurring at 59 months (1.1 per 100,000 doses for TIV without concomitant PCV13, 1.2 per 100,000 doses for PCV13 without concomitant TIV, and 4.0 per 100,000 doses for concomitant TIV and PCV13). Incidence rate ratio and risk difference estimates were lower for children receiving TIV without concomitant PCV13 or PCV13 without concomitant TIV. Because of the importance of preventing influenza and pneumococcal infections and associated complications, our findings should be placed in a benefit-risk framework to ensure that population health benefits are maximized.

A systematic review of validated methods for identifying seizures, convulsions, or epilepsy using administrative and claims data

PURPOSE

To systematically review algorithms to identify seizure, convulsion, or epilepsy cases in administrative and claims data, with a focus on studies that have examined the validity of the algorithms.

METHODS

A literature search was conducted using PubMed and the Iowa Drug Information Service database. Reviews were conducted by two investigators to identify studies using data sources from the USA or Canada because these data sources were most likely to reflect the coding practices of Mini-Sentinel data partners.

RESULTS

Eleven studies that validated seizure, convulsion, or epilepsy cases were identified. All algorithms included International Classification of Diseases, Ninth Revision, Clinical Modification code 345.X (epilepsy) and either code 780.3 (convulsions) or code 780.39 (other convulsions). Six studies included 333.2 (myoclonus). In populations that included children, 779.0 (convulsions in newborn) was also fairly common. Positive predictive values (PPVs) ranged from 21% to 98%. Studies that used nonspecific indicators such as presence of an electroencephalogram or anti-epileptic drug (AED) level monitoring had lower PPVs. In studies focusing exclusively on epilepsy as opposed to isolated seizure events, sensitivity ranged from 70% to 99%.

CONCLUSIONS

Algorithm performance was highly variable, so it is difficult to draw any strong conclusions. However, the PPVs were generally best in studies where epilepsy diagnoses were required. Using procedure codes for electroencephalograms or prescription claims for drugs possibly used for epilepsy or convulsions in the absence of a diagnostic code is not recommended. Many newer AEDs require no drug level monitoring, so requiring an AED level monitoring procedure in algorithms to identify epilepsy is not recommended.

Adverse events following 12 and 18 month vaccinations: a population-based, self-controlled case series analysis

Background

Live vaccines have distinct safety profiles, potentially causing systemic reactions one to 2 weeks after administration. In the province of Ontario, Canada, live MMR vaccine is currently recommended at age 12 months and 18 months.

Methods

Using the self-controlled case series design we examined 271,495 12 month vaccinations and 184,312 18 month vaccinations to examine the relative incidence of the composite endpoint of emergency room visits or hospital admissions in consecutive one day intervals following vaccination. These were compared to a control period 20 to 28 days later. In a post-hoc analysis we examined the reasons for emergency room visits and the average acuity score at presentation for children during the at-risk period following the 12 month vaccine.

Results

Four to 12 days post 12 month vaccination, children had a 1.33 (1.29–1.38) increased relative incidence of the combined endpoint compared to the control period, or at least one event during the risk interval for every 168 children vaccinated. Ten to 12 days post 18 month vaccination, the relative incidence was 1.25 (95%, 1.17–1.33) which represented at least one excess event for every 730 children vaccinated. The primary reason for increased events was statistically significant elevations in emergency room visits following all vaccinations. There were non-significant increases in hospital admissions. There were an additional 20 febrile seizures for every 100,000 vaccinated at 12 months.

Conclusions

There are significantly elevated risks of primarily emergency room visits approximately one to two weeks following 12 and 18 month vaccination. Future studies should examine whether these events could be predicted or prevented.

Active surveillance for adverse events: the experience of the Vaccine Safety Datalink project

OBJECTIVE

To describe the Vaccine Safety Datalink (VSD) project's experience with population-based, active surveillance for vaccine safety and draw lessons that may be useful for similar efforts.

PATIENTS AND METHODS

The VSD comprises a population of 9.2 million people annually in 8 geographically diverse US health care organizations. Data on vaccinations and diagnoses are updated and extracted weekly. The safety of 5 vaccines was monitored, each with 5 to 7 prespecified outcomes. With sequential analytic methods, the number of cases of each outcome was compared with the number of cases observed in a comparison group or the number expected on the basis of background rates. If the test statistic exceeded a threshold, it was a signal of a possible vaccine-safety problem. Signals were investigated by using temporal scan statistics and analyses such as logistic regression.

RESULTS

Ten signals appeared over 3 years of surveillance: 1 signal was reported to external stakeholders and ultimately led to a change in national vaccination policy, and 9 signals were found to be spurious after rigorous internal investigation. Causes of spurious signals included imprecision in estimated background rates, changes in true incidence or coding over time, other confounding, inappropriate comparison groups, miscoding of outcomes in electronic medical records, and chance. In the absence of signals, estimates of adverse-event rates, relative risks, and attributable risks from up-to-date VSD data have provided rapid assessment of vaccine safety to policy-makers when concerns about a specific vaccine have arisen elsewhere.

CONCLUSIONS

Care with data quality, outcome definitions, comparison groups, and length of surveillance are required to enable detection of true safety problems while minimizing false signals. Some causes of false signals in the VSD system were preventable and have been corrected, whereas others will be unavoidable in any active surveillance system. Temporal scan statistics, analyses to control for confounding, and chart review are indispensable tools in signal investigation. The VSD's experience may inform new systems for active safety surveillance.

Lack of association between acellular pertussis vaccine and seizures in early childhood

OBJECTIVES

Receipt of diphtheria-tetanus-whole-cell pertussis vaccine (diphtheria-tetanus toxoids-pertussis [DTP]) is associated with seizures. Limited population-based studies have been conducted on the risk for seizures after receipt of diphtheria-tetanus-acellular pertussis vaccine (diphtheria-tetanus-acellular pertussis [DTaP]).

METHODS

We conducted a retrospective study from 1997-2006 by using risk-interval cohort and self-controlled case series (SCCS) analyses on automated data at 7 managed care organizations that participate in the Vaccine Safety Datalink (VSD). Eligible children included the 1997-2006 VSD cohort of patients who were aged 6 weeks to 23 months and had not received DTP during the study period. A seizure event (febrile or afebrile) was defined by International Classification of Diseases, Ninth Revision, Clinical Modification diagnoses assigned to an inpatient or emergency department setting. The exposed period was composed of a predefined 4 person-days after each DTaP dose. All of the remaining observation periods outside the exposed periods were categorized as unexposed. The risk-interval cohort method compared the incidence of seizures between the exposed and unexposed cohorts. In the SCCS method, the comparison was performed between the same patient's exposed and unexposed period.

RESULTS

We identified 7191 seizure events among 433,654 children. The adjusted incidence rate ratio of seizures across all doses was 0.87 in cohort analysis and 0.91 in SCCS analysis.

CONCLUSIONS

We did not observe an increased risk for seizures after DTaP vaccination among children who were aged 6 weeks to 23 months. These findings provide reassuring evidence on the safety of DTaP with respect to seizures.

Measles-mumps-rubella-varicella combination vaccine and the risk of febrile seizures

OBJECTIVE

In February 2008, we alerted the Advisory Committee on Immunization Practices to preliminary evidence of a twofold increased risk of febrile seizures after the combination measles-mumps-rubella-varicella (MMRV) vaccine when compared with separate measles-mumps-rubella (MMR) and varicella vaccines. Now with data on twice as many vaccine recipients, our goal was to reexamine seizure risk after MMRV vaccine.

METHODS

Using 2000-2008 Vaccine Safety Datalink data, we assessed seizures and fever visits among children aged 12 to 23 months after MMRV and separate MMR + varicella vaccines. We compared seizure risk after MMRV vaccine to that after MMR + varicella vaccines by using Poisson regression as well as with supplementary regressions that incorporated chart-review results and self-controlled analyses.

RESULTS

MMRV vaccine recipients (83,107) were compared with recipients of MMR + varicella vaccines (376,354). Seizure and fever significantly clustered 7 to 10 days after vaccination with all measles-containing vaccines but not after varicella vaccination alone. Seizure risk during days 7 to 10 was higher after MMRV than after MMR + varicella vaccination (relative risk: 1.98 [95% confidence interval: 1.43-2.73]). Supplementary analyses yielded similar results. The excess risk for febrile seizures 7 to 10 days after MMRV compared with separate MMR + varicella vaccination was 4.3 per 10,000 doses (95% confidence interval: 2.6-5.6).

CONCLUSIONS

Among 12- to 23-month-olds who received their first dose of measles-containing vaccine, fever and seizure were elevated 7 to 10 days after vaccination. Vaccination with MMRV results in 1 additional febrile seizure for every 2300 doses given instead of separate MMR + varicella vaccines. Providers who recommend MMRV should communicate to parents that it increases the risk of fever and seizure over that already associated with measles-containing vaccines.

Vaccine safety: current systems and recent findings

PURPOSE OF REVIEW

An understanding of vaccine safety is important for all immunization providers, who have responsibilities to identify, report, and prevent adverse events.

RECENT FINDINGS

New analytic methods can provide more rapid information on adverse events compared with traditional observational studies. Some adverse events following vaccination are preventable. Syncope is increasingly recognized postvaccination and may be associated with severe injury or death. Both human and system factors should be addressed to prevent vaccine administration errors. Ongoing basic science and clinical research is critical to improved understanding of vaccine safety. A recent study suggests that many cases of encephalopathy following whole-cell pertussis vaccine were due to severe myoclonic epilepsy of infancy, a severe seizure disorder associated with mutations of the sodium channel gene SCN1A.

SUMMARY

Vaccine safety requires prelicensure evaluation, postlicensure surveillance and investigation, addressing preventable adverse events, reconsideration of vaccine policy as understanding of risks and benefits changes, and ongoing research to better understand the response to vaccination and the pathogenesis of adverse events.

Near real-time surveillance for influenza vaccine safety: proof-of-concept in the Vaccine Safety Datalink Project

The emergence of pandemic H1N1 influenza in 2009 has prompted public health responses, including production and licensure of new influenza A (H1N1) 2009 monovalent vaccines. Safety monitoring is a critical component of vaccination programs. As proof-of-concept, the authors mimicked near real-time prospective surveillance for prespecified neurologic and allergic adverse events among enrollees in 8 medical care organizations (the Vaccine Safety Datalink Project) who received seasonal trivalent inactivated influenza vaccine during the 2005/06-2007/08 influenza seasons. In self-controlled case series analysis, the risk of adverse events in a prespecified exposure period following vaccination was compared with the risk in 1 control period for the same individual either before or after vaccination. In difference-in-difference analysis, the relative risk in exposed versus control periods each season was compared with the relative risk in previous seasons since 2000/01. The authors used Poisson-based analysis to compare the risk of Guillain-Barré syndrome following vaccination in each season with that in previous seasons. Maximized sequential probability ratio tests were used to adjust for repeated analyses on weekly data. With administration of 1,195,552 doses to children under age 18 years and 4,773,956 doses to adults, no elevated risk of adverse events was identified. Near real-time surveillance for selected adverse events can be implemented prospectively to rapidly assess seasonal and pandemic influenza vaccine safety.