MMR Vaccine Doesn't Raise Infection Risk

Study Disputes 'Immune Overload' Theory

From the WebMD Archives

Feb. 20, 2003 -- Children who receive the combination measles, mumps, and rubella (MMR) vaccine are not more likely to become ill from a serious infection in the weeks following their vaccination, according to a new study. British researchers say the results dispute claims that the MMR vaccine overwhelms the immune system and makes children more susceptible to infection.

The MMR vaccine contains multiple antigens, which are substances that trigger an immune system response and lead to the creation of antibodies that defend the body against infection and disease. In this case, the vaccine is given to children during their second year of life to bolster their own natural defenses against the once-common childhood illnesses measles, mumps, and rubella.

Although researchers say there is no evidence that the use of the MMR vaccine increases the risk of infection from other causes, some have suggested that such combined vaccines may cause "immune overload."

To test this theory, researchers looked at the number of hospitalizations due to bacterial infections among children ages 12-23 months between 1991 and 1995 in several hospitals in southern England.

They found that hospitalization rates did not increase in the three months following MMR vaccination. In fact, the vaccine seemed to have a protective effect in the 90 days after inoculation and slightly reduced the number of bacterial infections reported.

Researcher Elizabeth Miller, MD, and colleagues of the Public Health Laboratory Service in London say the findings provide no evidence to support claims that the MMR vaccine might be increase the risk of illness among young children.

"It provides no support for either the concept of 'immune overload' resulting from simultaneous administration of three live attenuated viruses [antigens] to young children, or for the calls to provide single measles, mumps, and rubella in order to avoid such hypothetical effects," write the researchers.

SOURCE: Archives of Disease in Childhood, March 2003.

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