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Childhood vaccines are safe and effective, review of studies reconfirms

Investigators looked at 138 studies involving more than 23 million children. Among their findings: MMR vaccines did not cause encephalitis, inflammatory bowel disease, cognitive delay or any other suspected harm.

mmr vaccine
The review found that the MMR vaccines did not cause encephalitis, inflammatory bowel disease, cognitive delay or any other suspected harm. Nor did it cause autism.
REUTERS/Lindsey Wasson

The effectiveness and safety of vaccines for measles, mumps and rubella (MMR) have been reconfirmed in a major new review of the scientific evidence by Cochrane, a nonprofit global organization of independent scientific investigators.

The review also reconfirms that MMR vaccines are not associated with an increased risk of autism.

For the review, which was published this week in the Cochrane Database of Systematic Reviews, investigators looked at 138 studies involving more than 23 million children. Those studies included 74 that were conducted since the Cochrane’s last review on the topic, which was published in 2012. The earlier review reached conclusions similar to those in the current one.

Cochrane felt a need to update its review due to all the myths and conspiracy theories that have proliferated in recent years regarding vaccines in general and MMR vaccines in particular. That disinformation campaign has led to a drop in vaccinations — and a subsequent resurgence of outbreaks of the diseases around the world.

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The United States, for example, reported 1,282 cases of measles in 2019, the highest number in more than 25 years. Minnesota reported no measles cases in 2019, but in 2017, the state had 75 confirmed cases, mostly involving unvaccinated Somali-American children in Minneapolis. The Somali-American community had been targets of anti-vaccination propagandists.

A new threat is now impeding vaccination efforts. Last week, the World Health Organization raised concerns that more than 117 million children may be at risk of developing measles this year because countries have suspended immunization programs because of concerns about the coronavirus infection.

What the evidence shows

Of the 138 studies examined by the Cochrane reviewers, 51 (10+ million children) assessed effectiveness and 87 (13+ million children) assessed harms, including an association with autism. Some of the studies tested the measles, rubella and mumps (MMR) vaccine alone, while others tested it when it was either mixed with the chickenpox (varicella) vaccine (MMRV) or given separately at the same time (MMR+V).

Here’s what the review revealed in terms of the vaccine’s effectiveness:

  • A single does of the MMR vaccine was 95 percent effective in preventing measles. After two doses, effectiveness rose to about 96 percent.
  • For mumps, the MMR vaccine was 72 percent effective after a single dose and 86 effective after two doses.
  • For rubella, a single dose of the MMR vaccine was 89 percent effective in preventing the disease.
  • As for chickenpox, evidence showed that the MMRV vaccine was 95 percent effective in preventing that disease.

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“In terms of safety, we know from previous studies all around the world that the risks posed by these diseases far outweigh those of the vaccines administered to prevent them,” says Dr. Carlo Di Petrantonj, an epidemiologist at Italy’s Regional Epidemiology Unit SeREMI, in a released statement. “In this review, we wanted to look at evidence for specific harms that have been inked with these vaccines in public debate — often without rigorous scientific evidence as a basis.”

The review found that the MMR vaccines did not cause encephalitis, inflammatory bowel disease, cognitive delay or any other suspected harm.

Nor did it cause autism. In two studies (involving 1.1 million children) that investigated this topic, diagnosed cases of autism were found to be similar for vaccinated and unvaccinated children. For every 100,000 unvaccinated children, say the Cochrane reviewers, 451 diagnosed cases of autism could be expected. That compares to 419 cases among every 100,000 vaccinated children.

The studies found only two potential risks from the MMR vaccine. One of those risks involves febrile seizures, which are triggered by a fever that develops about two weeks after the vaccine is administered. As the Centers for Disease Control and Prevention points out on its website, nearly all children who have febrile seizures recover quickly and fully.

The other risk is a treatable rash-like condition where blood does not clot normally, known as idiopathic thrombocytopenic purpura, or ITP.

Those risks are quite small, however. And the benefits from the vaccines — preventing children from developing highly infectious diseases that can lead to serious complications, disability and death — far outweigh the risks.

“Our review shows that MMR, MMRV and MMR+V vaccines are effective in preventing the infections of children by measles, mumps, rubella and chickenpox, with no evidence of an increased risk of autism or encephalitis and a small risk of febrile seizures,” the reviewers conclude.

FMI:  You’ll find the review on Cochrane’s website.