MMR Vaccine: Weighing the Risks Versus Benefits

What is the MMR vaccine?

The measles, mumps and rubella (MMR) vaccine is a live virus vaccine that was introduced in 1963. It has significantly reduced the incidence of reported cases of measles, mumps and rubella infections; however, vaccine immunity wanes over time.

What are side effects of the MMR vaccine?

Common side effects of the MMR vaccine include fever, mild rash and swelling of glands in the cheeks or neck.

A more serious side effect is seizure, which occurs in about 1 in 640 children vaccinated with MMR — about five times more often than seizure from a measles infection.

Although severe potential side effects have been observed following MMR vaccination, including neurological disorders (e.g., encephalopathy, meningitis, ataxia, transverse myelitis, optic neuritis, multiple sclerosis, Guillain-Barré syndrome, brachial neuritis and hearing loss), autoimmune diseases (e.g., chronic arthritis), fibromyalgia and chronic fatigue syndrome, the Institute of Medicine states that “the evidence is inadequate to accept or reject a causal relationship between MMR vaccine” and those conditions.

Additionally, the manufacturer’s package insert states, “M-M-R II vaccine has not been evaluated for carcinogenic or mutagenic potential or impairment of fertility.”

How are risks of vaccine side effects measured?

Methods to measure vaccine risks include surveillance systems, clinical studies and epidemiological studies.

How accurate is surveillance of adverse events from the MMR vaccine?

The government tracks reported cases of vaccine side effects through the Vaccine Adverse Event Reporting System (VAERS). Approximately 40 cases of death and permanent injury from the MMR vaccine are reported to VAERS annually.

However, VAERS is a passive reporting system — authorities do not actively search for cases and do not actively remind doctors and the public to report cases. These limitations can lead to significant underreporting.

The Centers for Disease Control and Prevention (CDC) states, “VAERS receives reports for only a small fraction of actual adverse events.”

Indeed, as few as 1% of serious side effects from medical products are reported to passive surveillance systems, and as few as 1.6% of MMR-related seizures are reported to VAERS.

In addition, VAERS reports are not proof that a side effect occurred, as the system is not designed to thoroughly investigate all cases. As a result, VAERS does not provide an accurate count of MMR vaccine side effects.

How accurate are clinical trials of the MMR vaccine?

The CDC states, “Prelicensure trials are relatively small — usually limited to a few thousand subjects — and usually last no longer than a few years … Prelicensure trials usually do not have the ability to detect rare adverse events or adverse events with delayed onset.”

For children under age 10 at normal risk (i.e., with normal levels of vitamin A and infected after birth), the pre-vaccine annual risk of death or permanent disability from measles, mumps and rubella, respectively, was 1 in 1 million, 1 in 1.6 million and 1 in 2.1 million.

Therefore, the cumulative annual risk of a fatal or permanently disabling case of any of those diseases was about 1 in 500,000, and the risk over a 10-year span was 1 in 50,000.

A few thousand subjects in clinical trials are not enough to prove that the MMR vaccine causes less permanent disability or death than measles, mumps and rubella (Fig. 1).

In addition, the lack of adequate clinical trials of the MMR vaccine resulted in the manufacturer’s package insert data to be reliant on passive surveillance for rates of MMR-related neurological adverse reactions, permanent disability, and death.

There are not enough subjects in clinical trials to prove that the MMR vaccine poses less risk than measles, mumps and rubella.

How accurate are epidemiological studies of the MMR vaccine?

Epidemiological studies are hindered by the effects of chance and possible confounders — additional factors that could conceivably affect the groups being studied.

For example, there is a well-known 2002 Danish study published in the New England Journal of Medicine involving about 537,000 children that looked for an association between the MMR vaccine and certain adverse events.

The raw data in the study was adjusted in an attempt to account for potential confounders, and the study found no association between the MMR vaccine and the adverse events.

However, because there is no evidence that the estimated confounders used to adjust the raw data were actually confounders, the study did not rule out the possibility that the MMR vaccine increases the risk of an adverse event that leads to permanent injury by up to 77%.

Consequently, the study did not rule out the possibility that such adverse events might occur up to 21 times more often than death or permanent disability from measles, mumps and rubella in children at normal risk (i.e., with normal levels of vitamin A and infected after birth): 1 in 2,400 compared to 1 in 50,000 (see Fig. 2 and Table 1).

The range of possibilities found in the study, between the adjusted data and the raw data, makes the result inconclusive; even large epidemiological studies are not accurate enough to prove that the MMR vaccine causes less death or permanent injury than measles, mumps and rubella.

Is the MMR vaccine safer than measles, mumps and rubella?

It has not been proven that the MMR vaccine is safer than measles, mumps and rubella. The vaccine package insert raises questions about safety testing for cancer, genetic mutations and impaired fertility.

Although VAERS tracks some adverse events, it is too inaccurate to measure against the risk of measles, mumps and rubella. Clinical trials do not have the ability to detect less common adverse reactions and epidemiological studies are limited by the effects of chance and possible confounders.

Safety studies of the MMR vaccine are particularly lacking in statistical power. A review of more than 60 MMR vaccine studies conducted for the Cochrane Library states, “The design and reporting of safety outcomes in MMR vaccine studies, both pre- and post-marketing, are largely inadequate.”

Because permanent sequelae (aftereffects) from measles, mumps and rubella are so rare (especially in children with normal levels of vitamin A and infected after birth), the level of accuracy of the research studies available is insufficient to rule out the possibility that the MMR vaccine causes greater death or permanent disability than measles, mumps and rubella.

A 2002 Danish study did not rule out the possibility that the MMR vaccine can cause an adverse event leading to permanent disability 21 times more often than measles, mumps and rubella can be fatal or lead to permanent disability for U.S. children at normal risk (i.e., with normal levels of vitamin A and infected after birth).

Originally published by Physicians for Informed Consent.