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The Mystery of the MMR Reactions

Last October, an unusual outbreak of mumps occurred in Calgary and nearby Lethbridge, mainly among college students. To halt the spread, those aged 17 to 26 were urged to get a booster shot, and some 62,000 MMR (measles, mumps, rubella) boosters were given. But when six people developed symptoms similar to anaphylaxis, the program was abruptly stopped in December, and an investigation was begun.

Five people were sent to hospital by ambulance. Since then, Allergic Living has been trying to find out whether these were cases of anaphylaxis and if so, what caused them. While the Public Health Agency of Canada has not issued a public report and the investigating allergist would not speak to the media, Alberta health authorities will say that only one of the reactions was definitely anaphylaxis. Two reactions have been attributed to anxiety, and the causes of another two remain unknown. The sixth person refused to participate in the follow-up investigation.

There are trace amounts of egg protein in the MMR shot, but that is not considered a culprit in this situation. Recent clinical trials suggest that, under a revised manufacturing process, there is not enough egg protein in the vaccine to cause an allergic reaction. With egg ruled out, health authorities have gone to lengths test the individuals involved, as well as the vaccine.

Health Canada requested that the lots of the vaccine, manufactured by Merck & Co., be quarantined. Alberta Health hired an expert to review the cases and perform an allergy challenge in a medical setting on those who had reacted to the MMR vaccine. One person reacted again, while officials concluded that anxiety, which can mimic anaphylaxis in acute cases, caused reactions in two other cases. The reasons for the original symptoms in the remaining two subjects could not be resolved.

Meanwhile, the Public Health Agency of Canada investigated whether the suspected allergic reactions were caused by a factor other than the administering of the shots. For example, was there an interruption in the refrigeration of the vaccine as it was transported? For its part, Merck looked at its manufacturing process for the vaccines in question. Both found nothing wrong.

In short, health authorities are stumped. “The reactions appear to be related to the individual hosts, all of whom had a history of allergies and a history of at least one dose of a measles-containing vaccine in the past,” noted one health region.

The authorities are now considering the antibiotic called neomycin, found in the vaccine, as well as gelatin, used as a stabilizer, as possible causes. Dr. Mark Greenwald, a Toronto allergist, is surprised that gelatin hasn’t come under more scrutiny, since it’s derived from animal (pig) protein, and sensitivity to gelatin has been raised in studies elsewhere.

In 2002, the Centers for Disease Control and Prevention in Atlanta began to look at allergic reactions to gelatin after Japanese researchers found some sensitization in earlier Diphtheria Tetanus Pertussis vaccines. The U.S. researchers found that, among those with allergic reactions to the MMR vaccine, one-quarter had IgE antibody sensitivity (a marker of allergy) to gelatin.

Still reactions are rare. In Canada, millions of MMR shots have been given since 1988, with only been 21 reports of anaphylaxis.

With the vaccine program up and running again, Alberta Health suggests that anyone with known severe allergies to neomycin or gelatin discuss them with a physician prior to being immunized. Will that prevent any further reactions? At this point, no one can say for sure.

From the Fall 2008 issue of Allergic Living magazine.
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