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Girls more likely to visit hospital after 12-month MMR vaccine: study


Girls have an increased likelihood of reacting to the MMR vaccine given at 12 months of age than boys, according to a large, Ontario population-based study from researchers at the Institute for Clinical Evaluative Sciences (ICES) uOttawa, and the Ottawa Hospital Research Institute.

The MMR vaccine is an immunization vaccine against measles, mumps and rubella which is given at 12 months of age.

“This study indicates that girls may respond differently to the measles vaccine than boys, which could indicate general sex differences in the response to the measles virus,” says study author Steven Hawken, a senior methodologist at the Ottawa Hospital Research Institute, lead analyst at ICES uOttawa and PhD candidate at the University of Ottawa.

While pediatric vaccinations have been clearly demonstrated to be safe and effective, the process of creating immunity can cause mild reactions that may result in the use of health-care services.

Published by Vaccine, the researchers examined records for all children born in Ontario between April 1, 2002 and March 31, 2009, correlating ER visits and hospital admissions following each of the two, four, six and 12-month vaccinations to investigate the effect of sex on relative incidence of these events. The study found:

  • At 12 months, the time of receipt of the MMR vaccine, girls were associated with a significantly higher relative incidence of events (ER visits and hospital admissions).
  • Females had 192 more events per 100,000 vaccinated compared to the number of events that would have occurred in 100,000 vaccinated males.

The study identified no significant relationship between the relative incidence of an event and sex of the child after immunizations at 2, 4 and 6 months, which are non-measles containing vaccines.

The authors stress that their findings support the current measles vaccination programs in Ontario, but also point to a need for further investigation into physiological reasons for the different sex response to the measles virus and measles-containing vaccines.

“Our findings suggest that there may be important physiological differences between boys and girls that explain the different response to the 12-month vaccine,” said Dr. Kumanan Wilson, senior author of the study, a scientist at the Ottawa Hospital Research Institute and adjunct scientist at ICESuOttawa.

The study “Increased emergency room visits or hospital admissions in females after 12-month MMR vaccination, but no difference after vaccinations given at a younger age,” is published online by Vaccine, and will be included in a forthcoming issue of the journal.

Authors: Wilson K, Ducharme R, Ward B and Hawken S.

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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About the Ottawa Hospital Research Institute (OHRI) The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and is an affiliated institute of the University of Ottawa, closely associated with the university’s Faculties of Medicine and Health Sciences. OHRI includes more than 1,700 scientists, clinical investigators, graduate students, postdoctoral fellows and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease. Research at OHRI is supported by The Ottawa Hospital Foundation.

For the latest OHRI news, visit: www.ohri.ca


  • Deborah Creatura
  • Communications, ICES
  • [email protected]
  • (o) 416-480-4780 or (c) 416-904-4547
  • Paddy Moore
  • Ottawa Hospital Research Institute
  • [email protected]
  • (o) 613-737-8899 x73687 or (c) 613-323-5680

Read the Journal Article