Updated Review Examines MMR Vaccine Safety and Efficacy

Measles, mumps, rubella, and chickenpox are serious, but vaccine-preventable diseases. Measles can infect every organ system and in some circumstances may lead to a wide range of complications such as hepatitis, appendicitis and viral meningitis.

Vaccine hesitancy and vaccine misinformation have colored public debate over the safety of the measles, mumps, rubella (MMR) vaccine, despite near universal use and acceptance among clinicians.

A team of experts from Italian public health institutions published an article in the Cochrane Database of Systematic Reviews which sought to assess the safety, effectiveness, and adverse effects associated with the trivalent MMR vaccine, the administration of MMR vaccine with a varicella vaccine, and tetravalent vaccines containing MMR and varicella strains given to children up to 15 years of age. The review is an update of analyses published in 2005 and 2012.

Study authors searched the Cochrane Central Register of Controlled Trials, MEDLINE, clinicaltrials.gov, and the World Health Organization Clinical Trials Registry Platform.

The investigators included randomized controlled trials, controlled clinical trials, prospective and retrospective cohort studies, interrupted time series studies, case control studies, and case-coverage design/screening method studies which pertained to relevant vaccines given in any dose or schedule.

Studies were grouped according to study design, vaccine type, viral strain, and study setting. A team of 2 review authors independently assessed the methodological quality of included studies. The review contains 138 studies spanning over 23 million participants. Of these studies, 51 assessed vaccine efficacy, while 87 assessed the association between vaccines and adverse events.

Ultimately, 74 new studies were incorporated into the updated version of the review.

The vaccine effectiveness for measles prevention was calculated to be 95% after a single dose (RR: .05, 95% CI, .02—.13.

Vaccine effectiveness was 96% after administration of 2 doses (RR .04, 95% CI .01—.28).

Among household contacts, the effectiveness of vaccination to prevent transmission to other children after a single dose was 81% (RR 0.19, 95% CI .04— .89), 85% after 2 doses, and 96% after 3 doses (RR .04, 95% CI .01–.23).

Effectiveness of at least 1 dose in prevention of measles when the vaccine was used as post-exposure prophylaxis was 74%, with evidence considered lower certainty by review authors.

For mumps prevention, Jeryl Lynn containing MMR vaccine was 72% effective after 1 dose (RR .24, 95% CI .08— .76) and 86% after 2 doses (RR .12, 95% CI .04–.35).

Against rubella, vaccine effectiveness was 89% (RR .11, 95% CI .03—.42). Against varicella of any severity, 2 doses had a 95% effectiveness after 10 years follow-up (95% CI .03 –.08).

Safety evaluations provided evidence of an association between some adverse events and the MMR vaccine, but not others. Vaccine safety also varied based on strains used.

“There is evidence supporting an association between aseptic meningitis and MMR vaccines containing Urabe and Leningrad‐Zagreb mumps strains, but no evidence supporting this association for MMR vaccines containing Jeryl Lynn mumps strains (RR 1.30, 95% CI .66—2.56; low certainty evidence),” the authors wrote.

The analyses also provided evidence supporting an association between the Jeryl Lynn strain vaccines studied and febrile seizures. These seizures occur in between 2% to 4% of healthy children before the age of 5. The risk attributable to vaccines is estimated to be between 1 per 1700 and 1 per 1150 doses administered.

There was evidence for association between MMR vaccination and idiopathic thrombocytopenic purpura, though the risk after vaccination is 1 case per 40,000 vaccinations compared to 1 case per 20,000 natural infections per year.

The invesitgators did not find evidence of an association between MMR immunization with encephalitis or encephalopathy. They also did not find an association with autism spectrum disorder. There was also no evidence supporting association between MMR vaccination and cognitive delays, asthma, hay fever, leukemia, multiple sclerosis, or bacterial and viral infections.

Evidence was insufficient to determine if there is an association between MMR vaccines and inflammatory bowel disease, according to the review authors.

“Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunization. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage,” the authors concluded.