Evaluating adverse events after vaccination in the medicare population
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Evaluating Adverse Events after Vaccination in the Medicare Population. Robert Ball, MD, MPH, ScM Chief, Vaccine Safety Branch Division of Epidemiology CBER, FDA FDA/Industry Statistics Workshop September 29, 2006. Collaborators. CMS Lawrence La Voie, Peter Houck, Rebecca Hudson

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Evaluating Adverse Events after Vaccination in the Medicare Population

Robert Ball, MD, MPH, ScM

Chief, Vaccine Safety Branch

Division of Epidemiology

CBER, FDA

FDA/Industry Statistics Workshop

September 29, 2006


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Collaborators Population

  • CMS

    • Lawrence La Voie, Peter Houck, Rebecca Hudson

  • FDA/CBER

    • Dale Burwen, Miles Braun


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Medicare and Vaccine Safety: Background Population

  • Post-licensure observational studies using large linked databases can provide important data about whether adverse events are associated with vaccines.

  • Serious adverse events requiring hospitalization after vaccination are uncommon, but are important to evaluate to ensure safe vaccination and maintain the public’s confidence in vaccination.

  • Medicare data can help fill an important need because other databases may not have sufficient statistical power to examine rare events, and may under represent the elderly.


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Medicare and Vaccine Safety: Background Population

  • ~ 41 million Medicare beneficiaries (96% of ≥ 65 year olds in US).

    • ~35 million ≥ 65 years old.

    • 6 million are younger with disabilities or end stage renal disease.

  • Key consumers of influenza and pneumococcal vaccines.

    • Nearly all of the elderly, and many younger beneficiaries, are recommended to receive the vaccines based on their high disease risk.

    • According to the CDC, routine revaccination of immunocompetent persons previously vaccinated with pneumococcal vaccine is not recommended, although revaccination once is recommended for certain persons provided that 5 years have elapsed since receipt of the first dose, and revaccination following a second dose is not routinely recommended.

  • Pneumococcal and influenza vaccination have been covered benefits in the Medicare program since 1981 and 1993, respectively.


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Medicare and Vaccine Safety: PopulationStudy Questions

  • Can Medicare data be used to evaluate adverse events after influenza and pneumococcal vaccines?

    • Is hospitalization for urinary tract infection (UTI), not likely associated with vaccination, or for cellulitis and abscess of the upper arm and forearm (CAUAF) associated with vaccination?

    • What are the data quality issues relevant to vaccine safety analyses?


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Methods: Description of Study and Statistical Analysis Population

  • Case series design to evaluate the frequency of hospitalization during the period immediately after vaccination compared with the average frequency during the periods before and after vaccination.

    • Only persons who both were vaccinated and were hospitalized for the selected condition were included.

    • 7 days immediately preceding vaccination were excluded because of the healthy vaccinee effect; vaccinated persons are less likely to be acutely ill and hospitalized.

    • Determined the average frequency based on 54 days (days 8 to 30 prior to vaccination and days 0 to 30 after vaccination).

    • Tested whether the frequency of hospitalization deviated from a uniform distribution equal to the average frequency using the χ2 goodness-of-fit test.

    • If the observed frequency during the 54 days deviated from the uniform distribution, we tested whether the deviation localized to the week after vaccination by omitting days 0 to 7, and repeating the χ2 goodness-of-fit test for deviation from a uniform distribution.

  • Among the cohort of persons who received pneumococcal vaccine in 2001, we evaluated whether prior receipt of vaccine and shorter interval between vaccinations (<5 years) were risk factors for hospitalization for cellulitis and abscess of the upper arm and forearm (CAUAF).

    • Proportions were compared using χ2.


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Methods: Data Quality Assessment Population

  • To assess agreement with other data sources, we compared vaccine coverage rates using Medicare claims data to published rates obtained from survey data including:

    • Agency for Healthcare Research and Quality’s (AHRQ) Consumer Assessment of Health Plan Surveys® (CAHPS)

    • CMS Medicare Current Beneficiary Survey (MCBS)

    • Centers for Disease Control and Prevention’s (CDC) National Health Information Survey (NHIS)

    • State-based Behavioral Risk Factor Surveillance System (BRFSS)


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Methods: Data Sources Population

  • Data from the National Claims History File and Enrollment Database for 2001

  • 2001 Medicare 5% sample and the 1991-2001 Pneumococcal Vaccine File


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Interval Between Influenza Immunization and Admission Date for Selected Conditions

Number of Hospitalizations

Days before vaccination Days after vaccination

Date of

vaccination


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Interval Between Pneumococcal Immunization and Admission Date for Selected Conditions

Number of Hospitalizations

Days before vaccination Days after vaccination

Date of

vaccination


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Interval Between Receipt of Last Two Pneumococcal Vaccines, Among Persons Vaccinated in 2001

Number of Persons

Years


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TABLE 1. Influenza Vaccination Rates (per 100), Persons Age 65+, by Data Source

Influenza Vaccination Rates (per 100), Persons Age 65+, by Data Source

Abbreviations: CAHPS, Consumer Assessment of Health Plan Surveys; MCBS, Medicare Current Beneficiary Survey; NHIS, National Health Interview Survey; BRFSS, Behavioral Risk Factor Surveillance System; NA, published results not available.


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TABLE 2. Pneumococcal Vaccination Rates (per 100), Persons Age 65+, by Data Source

TABLE 1. Influenza Vaccination Rates (per 100), Persons Age 65+, by Data Source

Pneumococcal Vaccination Rates (per 100), Persons Age 65+, by Data Source

Abbreviations: CAHPS, Consumer Assessment of Health Plan Surveys; MCBS, Medicare Current Beneficiary Survey; NHIS, National Health Interview Survey; BRFSS, Behavioral Risk Factor Surveillance System; NA, published results not available.


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Conclusions Age 65+, by Data Source

  • Using Medicare administrative data, we identified a possible increased risk of hospitalization for cellulitis and abscess of the upper arm and forearm after pneumococcal vaccine, but not influenza vaccine.

    • This risk of hospitalization was not detected in smaller studies.

    • Injection site reactions are likely to often be misdiagnosed as cellulitis. These data are consistent with the known local reactogenicity of pneumococcal vaccine.

    • The revaccination rate for pneumococcal vaccine is higher than expected and the interval of revaccination in some cases is shorter than expected (<5 years) based on current recommendations.


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Conclusions Age 65+, by Data Source

  • A potential limitation of Medicare data identified is the difference in vaccination rates between claims data and survey data.

    • This limitation can be addressed using the case series study design, where only individuals who have both the condition under study and received the vaccine are included.

  • Screening analyses can be performed using administrative data, but medical record review to validate diagnoses will often be needed for rigorous study of vaccine-adverse event associations.

  • Current and future projects include the evaluation of Guillain Barre Syndrome after influenza vaccine, cellulitis after pneumococcal polysaccharide vaccine, and pandemic influenza vaccine safety preparedness.



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