Study finds serious reactions to MMR vaccine uncommon

The measles, mumps and rubella (MMR) vaccine has been used extensively in children and has been demonstrated to be safe and highly effective in preventing disease. However, in the process of conferring immunity, the vaccines have the potential to cause adverse reactions one to two weeks after administration.

In Ontario, during the time period of the study, the MMR vaccine was administered at age 12 months, with a booster at 18 months. In a new study conducted at the Institute for Clinical Evaluative Sciences (ICES) and the Ottawa Hospital Research Institute (OHRI), there were elevated risks of emergency room visits approximately one to two weeks following the 12- and 18-month vaccinations.

“It’s important for parents to know that these rare reactions can occur after the MMR vaccine; they are expected and are part and parcel of the vaccine and immune system working. However, they may be scary to patients and parents and may be contributing to the anxiety and unfounded concerns about the vaccine,” says Dr. Kumanan Wilson, lead author, adjunct scientist at ICES and scientist at OHRI.

The study of all Ontario children born between April 1, 2006, and March 31, 2009, found that:

• Four to 12 days after the 12-month vaccination, for every 168 children vaccinated, one child was seen at a hospital with symptoms that were related to the vaccine.
• Ten to 12 days after the 18-month vaccination, the figure was one in every 730 children vaccinated.
• The primary reason for increased events was elevations in emergency room visits.
• There was one additional febrile seizure for every 5,000 children vaccinated at age 12 months.
• There was no impact on deaths.

“In Europe this year, there have been more than 26,000 cases of measles and nine deaths. In Quebec, there have been 750 cases, and under-vaccination of children is believed to be responsible. The fear of a rare adverse effect should not deter parents from having their children vaccinated against completely preventable diseases,” says Wilson.

Author block: Kumanan Wilson, Steven Hawken, Jeffrey C Kwong, Shelley Deeks, Natasha S Crowcroft, Carl van Walraven, Beth K Potter, Pranesh Chakraborty, Jennifer Keelan, Michael Pluscauskas, Doug Manuel.

The study “Adverse events following 12 and 18 month vaccinations: a population-based, self-controlled case series analysis” is in the December 12, 2011, issue of PLoS One.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

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