A new review of data from more than 20 million children shows that the MMR vaccine, which protects against measles, mumps, and rubella, is effective and not associated with autism.
Health authorities licensed the MMR vaccine for use in 1971 after tests showed that adverse reactions from the combined vaccine were no greater than any from the existing, single vaccines.
Governments have since rolled the vaccine out across the globe, leading to the eradication of measles in many countries, including the United States.
Despite this, the vaccine has been the subject of much controversy, in particular, due to a 1998 study linking the vaccine to autism. The study was later shown to be fraudulent and was discredited, but not before it received wide publicity, leading to public misconceptions about the vaccine.
An updated review of the evidence has now confirmed that the MMR vaccine is effective and not associated with autism.
The Cochrane Library, which surveys medical research to help health professionals make evidence-based decisions, has published the review.
The latest analysis follows a 2012 review, which concluded that there was good evidence for the safety and effectiveness of the MMR vaccine. This 2020 update includes 74 new studies that researchers have published since 2012.
“We wanted to assess the effectiveness, safety, and long- and short-term harms of the MMR vaccines in this updated review,” explains lead author, Dr. Carlo Di Pietrantonj of Italy’s Regional Epidemiology Unit, SeREMI.
The updated review includes data on three types of vaccine: MMR; MMRV, which is a combined vaccine that also protects against chickenpox (known clinically as varicella); and MMR+V, which is when healthcare professionals give the MMR vaccine and chickenpox vaccine separately but at the same appointment.
In total, the review included 138 studies with data from 23 million children. Some 63% of the studies assessed potential harms from the vaccines (13 million children), while the remaining 37% (10 million children) looked at how effective the vaccines were at preventing the respective diseases.
The review found that one dose of the MMR vaccine was 72% effective in preventing mumps, which can cause flu-like symptoms and severe swelling of the salivary glands.
Success rates increase to 86% after two doses of the vaccine. From the data the review analyzed, the number of mumps cases would fall from roughly 7% unvaccinated children to 1% of children when they received two doses of the MMR vaccine.
For measles, the success rates are much higher. The review found that just one dose of the vaccine would prevent 95% of cases. Receiving two doses of the vaccine is similarly effective and would prevent a further 1% of cases. Vaccinating children with just one dose of MMR would reduce the overall number of measles cases from 7% to below 0.5%, the statistics show.
One dose of the vaccine was found to be 89% effective in preventing rubella.
Rubella causes a rash in children but can be serious if a woman contracts it during pregnancy, potentially leading to miscarriage or causing deafness in the child.
Data on chickenpox, meanwhile, showed that two doses of the vaccine can prevent 95% of cases, even after 10 years. However, the data on chickenpox was from just one study.
While clearly effective at preventing viral disease, there are risks from vaccination. Some children may develop a fever or rash following vaccination, for example.
The researchers also identified certain associations with the MMR vaccines, such as experiencing fits due to high temperature and a blood clotting condition called idiopathic thrombocytopenic purpura.
However, the research team says the risk of these occurring (less than a 1% chance in both cases) is much lower than the risks that the diseases themselves pose.
The scientists also wanted to look specifically at other risks that the public perceives, such as autism.
“We wanted to look at evidence for specific harms that have been linked with these vaccines in public debate — often without rigorous scientific evidence as a basis,” explains Dr. Pietrantonj.
The review summarizes data from two studies with almost 1.2 million children that show that the rates of autism diagnosis are similar in those receiving the MMR vaccine and those who do not.
The researchers also found no evidence for a connection with a host of other diseases the public has previously linked to the vaccine, including encephalitis, diabetes, inflammatory bowel disease, and asthma.
On the basis of this data, the scientists continue to recommend the MMR vaccines for global use.
“Overall, we think that existing evidence on the safety and effectiveness of MMR/MMRV/MMR+V vaccines supports their use for mass immunization,” says Dr. Pietrantonj.
The Cochrane study is an important reminder of the efficacy and importance of the MMR vaccine, particularly in the fight against measles.
Despite the availability of the vaccine, more than 140,000 people died from measles in 2018 alone, data from the World Health Organization (WHO) show.
Measles remains a leading cause of death in children and there are concerns about a growing number of cases, partly due to anti-vaccination movements.
These trends are of serious concern for child health. The data from this latest research may provide reassuring evidence on the safety and effectiveness of the MMR vaccine, while supporting continuing efforts to eliminate the disease worldwide.