Evidence of herd immunity and sustained impact of rotavirus vaccination on the reduction of rotavirus-related medical encounters among infants from 2006 through 2011 in the United States.

BACKGROUND: Rotavirus (RV) is the leading cause of severe acute gastroenteritis among young children. Since the US licensure of the pentavalent RV vaccine (RV5) and the monovalent RV vaccine (RV1), a decline of RV activity has been observed. OBJECTIVE: To describe patterns of RV-related health care utilization among infants receiving RV vaccines (RVVs). METHODS: A large national health insurance claims database was used to identify infants born from January 2002 through July 2011. From this cohort, infants were divided into three groups: (1) those who received a RVV, (2) those receiving a diphtheria, tetanus, and acellular pertussis (DTaP) vaccine before the introduction of RVV (February 2006), and (3) those receiving DTaP without a concurrent RVV during the period of RVV availability. Study outcomes were rotavirus gastroenteritis (RGE) and acute gastroenteritis. Longitudinal, seasonal RGE incidence patterns among the RVV cohort (n = 140,952) were compared with the referent DTaP-vaccine cohort (n = 131,529). RESULTS: More than 91% of administered RVV were RV5. Mean peak incidence of RV medical encounters in RV-vaccinated infants was 95-96% lower than among DTaP-vaccinated infants who did not receive RVV. RGE incidence among the non-RV-vaccinated DTaP recipients in the RVV-available period (110 per 100,000 infants) was lower than among DTaP recipients in the pre-RVV period (151 per 100,000 infants). The highest RGE incidence in the 2007-2011 period was among older non-RV-vaccinated infants. CONCLUSIONS: Analysis of a national medical claims database indicates a sustained and substantial decrease in the seasonal RV medical claims pattern after the introduction of RVV. This analysis also reveals evidence of herd immunity, although unvaccinated infants continue to be at risk and contribute to smaller seasonal peaks in RV disease activity.

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.

Evaluating the safety of influenza vaccine using a claims-based health system.

INTRODUCTION: As part of the Centers for Disease Control and Prevention's monitoring and evaluation activities for influenza vaccines, we examined relationships between influenza vaccination and selected outcomes in the 2009-2010 and 2010-2011 influenza seasons in a claims-based data environment. METHODS: We included patients with claims for trivalent influenza vaccine (TIV) and/or 2009 pandemic influenza A H1N1 vaccine (H1N1) during the 2009-2010 and 2010-2011 influenza seasons. Patients were followed for several pre-specified outcomes identified in claims. Seizures and Guillain-Barré Syndrome were selected a priori for medical record confirmation. We estimated incidence rate ratios (IRR) using a self-controlled risk interval (SCRI) or a historical comparison design. Outcomes with elevated IRRs, not selected a priori for medical record review, were further investigated with review of claims histories surrounding the outcome date to determine whether the potential event could be ruled-out or attributed to other causes based on the pattern of medical care. RESULTS: In the 2009-2010 season, no significant increased risks for outcomes following H1N1 vaccination were observed. Following TIV administration, the IRR for peripheral nervous system disorders and neuropathy was slightly elevated (1.07, 95% CI: 1.01-1.13). The IRR for anaphylaxis following TIV was 28.55 (95% CI: 3.57-228.44). After further investigation of claims histories, the majority of potential anaphylaxis cases had additional claims around the time of the event indicating alternate explanatory factors or diagnoses. In the 2010-2011 season following TIV administration, a non-significant elevated IRR for anaphylaxis was observed with no other significant outcome findings. CONCLUSION: After claims history review, we ultimately found no increased outcome risk following administration of 998,881 TIV and 538,257 H1N1 vaccine doses in the 2009-2010 season, and 1,158,932 TIV doses in the 2010-2011 season.