Jul 2, 2014
Published in: Evidence Report/Technology Assessment No. 215 (Prepared by Southern California/RAND Evidence-Based Practice Center, under Contract No. 290-2007-10062-1). AHRQ Publication No. 14-E002-EF. (Rockville, MD: Agency for Healthcare Research and Quality, July 2014), 740 p
Posted on RAND.org on July 01, 2014
OBJECTIVES: To conduct a systematic review of the literature on the safety of vaccines recommended for routine immunization of children, adolescents, and adults in the United States as of 2011. REVIEW METHODS: We reviewed the methodology of the 2011 Institute of Medicine (IOM) consensus report "Adverse Effects of Vaccines: Evidence and Causality" and accepted their findings. We augmented their work with new studies and additional vaccines. We were unable to pool results; we rated the overall strength of evidence (SOE) as high, moderate, low, or insufficient. RESULTS: A total of 20,478 titles were identified; after title, abstract, and full-text review, 166 studies were accepted for abstraction. The vast majority of studies either did not investigate or could not identify risk factors for adverse events (AEs) associated with vaccination. Similarly, the severity of AEs was inconsistently reported, as was information that would make independent severity determination possible. SOE was high for the following associations in nonpregnant adults: seasonal influenza vaccine and arthralgia, myalgia, malaise, fever, pain at injection site; 2009 monovalent H1N1 vaccine and Guillain-Barré syndrome (GBS); and a lack of association between influenza and pneumococcal vaccines and cardiovascular events in the elderly. Risk of GBS was estimated at 1.6 excess cases per million persons vaccinated. SOE was high for the following associations in children and adolescents: measles, mumps, rubella (MMR) vaccine and febrile seizures in children under age 5; lack of association between MMR vaccine and autism spectrum disorders; and varicella vaccine and disseminated Oka strain varicella zoster virus with associated complications (i.e., meningitis, encephalitis) in individuals with demonstrated immunodeficiencies. There is moderate SOE that vaccines against rotavirus are associated with intussusception in children; risk was estimated as 1 to 5 cases per 100,000 vaccine doses, depending on brand. Moderate-strength evidence exists regarding human papillomavirus vaccine and a lack of association with onset of juvenile rheumatoid arthritis, type 1 diabetes, and GBS. Moderate-strength evidence shows no association between inactivated influenza vaccine and serious AEs in pregnant women. Evidence was insufficient to make conclusions regarding whether several routinely recommended vaccines are associated with serious conditions such as multiple sclerosis, transverse myelitis, and acute disseminated encephalomyelitis. CONCLUSIONS: There is evidence that some vaccines are associated with serious adverse events; however, these events are extremely rare and must be weighed against the protective benefits that vaccines provide. Careful consideration should be given to the investigation of research gaps, including patient risk factors that may be associated with AEs; however, important factors must be taken into account when determining whether studies are warranted, including the severity and frequency of the AE being studied and the challenges of conducting sufficiently powered studies when investigating rare events.