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Severe vaccine complications are rare, review finds

BMJ 2014; 349 doi: (Published 03 July 2014) Cite this as: BMJ 2014;349:g4411
  1. Michael McCarthy
  1. 1Seattle, USA

Although some childhood vaccines are associated with severe adverse events, these complications are “extremely” rare, according to a new systematic review.1

The review, which updates and adds to the 2011 Institute of Medicine (IOM) report entitled Adverse Effects of Vaccines: Evidence and Causality, was commissioned by the US Agency for Healthcare Research and Quality to identify gaps in evidence on the safety of vaccines.2

The review focused on vaccines recommended for routine use in the US for children aged 6 years and younger: DTaP (diphtheria, tetanus, and acellular pertussis); hepatitis A; hepatitis B, haemophilus influenza type b (Hib); influenza (live attenuated and inactivated); meningococcal (conjugate or polysaccharide); measles, mumps, and rubella (MMR); pneumococcal (conjugate or polysaccharide); rotavirus; and varicella.

The study excluded studies of vaccine formulations never used or no longer available in the US, such as whole cell pertussis vaccine, oral polio vaccine, and pneumococcal conjugate vaccine 7 vaccine.

Margaret Maglione of the RAND Corporation, an independent research non-profit making organisation based in Santa Monica, California, was the lead author of the paper, which was published online on 1 July in the journal Pediatrics.

Of 20 478 titles identified through electronic literature searches and reviews of product inserts, US Food and Drug Administration documents, and other sources, the researchers found 67 studies that met their inclusion criteria.

The researchers found that the strength of evidence linking febrile seizures to the MMR vaccine was “high.” However, they had “high” confidence that the evidence did not support an association between the MMR vaccine and autism.

A “high” rating indicates that the researchers have high confidence that the evidence reflects a true effect, and that further research is “very unlikely” to change their estimate of effect.

The researchers found a moderate (but consistent) strength of evidence of an association between the MMR vaccine and thrombocytopenic purpura in children and between the varicella vaccine and thrombocytopenic purpura in children aged 11-17 years.

A “moderate” ranking indicates that researchers have moderate confidence that the evidence reflects the true effect, but that further research may change their “confidence in the estimate of effect and may change the estimate.”

None of the vaccines studied was associated with an increased risk of childhood onset leukemia, the researchers write.

Analysis of 31 trials of rotavirus vaccines, whose safety was not assessed in the IOM report, provided moderate strength evidence of an association between rotavirus vaccination and intussusception, the researchers write, although this complication was extremely rare. One study, for example, found rates of 1.1-1.5 cases per 100 000 doses of RotaTeq and 5.1 cases per 100 000 doses of Rotarix.

In an accompanying commentary, Carrie Byington of the Department of Pediatrics of the University of Utah in Salt Lake City, Utah, writes that the findings of this new study and those of the IOM report “should be reassuring to parents of young children and to the clinicians who care for them.”3

The assessments should give providers greater confidence in their advocacy for vaccines, she writes. “Ideally, provider confidence in vaccine safety will increase the confidence of the families they serve and increase vaccination rates for children, safe-guarding the health of the nation.”


Cite this as: BMJ 2014;349:g4411


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