Journal Article

Causality assessment of serious neurologic adverse events following 2009 H1N1 vaccination

Pahud, Barbara A., Dekker, Cornelia L., Sparks, Robert C., Aukes, Laurie L., Sejvar, James J., McGeeney, Brian E., Klein, Nicola P., Baxter, Roger P., Marchant, Colin D., Jakob, Kathleen, Edwards, Kathryn M., Coronel, Silvia, LaRussa, Philip S., Tokars, Jerome I., Vellozzi, Claudia, Halsey, Neal, Williams, S. Elizabeth, Slade, Barbara A., Barnett, Elizabeth D., Donofrio, Peter D.

2011

Overview

► We reviewed 212 neurological SAEs after H1N1 vaccine reported to VAERS. ► We applied modified WHO causality criteria to case reports. ► The most frequent diagnoses were GBS (37%) and seizure (11%). ► Causal assessment resulted in 72 possible, 108 unlikely, and 20 unrelated to vaccine. Adverse events occurring after vaccination are routinely reported to the Vaccine Adverse Event Reporting System (VAERS). We studied serious adverse events (SAEs) of a neurologic nature reported after receipt of influenza A (H1N1) 2009 monovalent vaccine during the 2009–2010 influenza season. Investigators in the Clinical Immunization Safety Assessment (CISA) network sought to characterize these SAEs and to assess their possible causal relationship to vaccination. Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) physicians reviewed all SAE reports (as defined by the Code of Federal Regulations, 21CFR§314.80) after receipt of H1N1 vaccine reported to VAERS between October 1, 2009 and March 31, 2010. Non-fatal SAE reports with neurologic presentation were referred to CISA investigators, who requested and reviewed additional medical records and clinical information as available. CISA investigators assessed the causal relationship between vaccination and the event using modified WHO criteria as defined. 212 VAERS reports of non-fatal serious neurological events were referred for CISA review. Case reports were equally distributed by gender (50.9% female) with an age range of 6 months to 83 years (median 38 years). The most frequent diagnoses reviewed were: Guillain–Barré Syndrome (37.3%), seizures (10.8%), cranial neuropathy (5.7%), and acute disseminated encephalomyelitis (3.8%). Causality assessment resulted in classification of 72 events as “possibly” related (33%), 108 as “unlikely” related (51%), and 20 as “unrelated” (9%) to H1N1 vaccination; none were classified as “probable” or “definite” and 12 were unclassifiable (6%). The absence of a specific test to indicate whether a vaccine component contributes to the pathogenesis of an event occurring within a biologically plausible time period makes assessing causality difficult. The development of standardized protocols for providers to use in evaluation of adverse events following immunization, and rapid identification and follow-up of VAERS reports could improve causality assessment.

• Publisher: Elsevier Ltd,Elsevier,Elsevier Limited
• Subject: Adolescent / Adult / Adverse event following immunization / Aged / Aged, 80 and over / Allergy and Immunology / Applied microbiology / Biological and medical sciences / case studies / Causality assessment / Centers for Disease Control and Prevention / Child / Child, Preschool / Cranial Nerve Diseases - chemically induced / Cranial Nerve Diseases - epidemiology / Drug therapy / encephalitis / Encephalomyelitis, Acute Disseminated - chemically induced / Encephalomyelitis, Acute Disseminated - epidemiology / Female / Food and Drug Administration / Fundamental and applied biological sciences. Psychology / gender / Guillain-Barre Syndrome / Guillain-Barre Syndrome - chemically induced / Guillain-Barre Syndrome - epidemiology / H1N1 vaccine / Humans / Immunization / Infant / influenza / Influenza A Virus, H1N1 Subtype - immunology / Influenza Vaccines - administration & dosage / Influenza Vaccines - adverse effects / Male / Microbiology / Middle Aged / Nervous System Diseases - chemically induced / Nervous System Diseases - epidemiology / pathogenesis / physicians / safety assessment / seizures / Swine flu / vaccination / Vaccination - adverse effects / Vaccines / Vaccines, antisera, therapeutical immunoglobulins and monoclonal antibodies (general aspects) / World Health Organization / Young Adult