Two doses of mumps vaccine superior to one

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The analysis of a recent Ontario, Canada, mumps outbreak has indicated that two doses of mumps vaccine are more effective than one, showing renewed importance that people be up to date on their mumps vaccinations.

Researchers from the Ontario Agency for Health Protection and Promotion, the Ontario Ministry of Health and Long-term Care, the University of Toronto and the North Bay Regional Health Unit in Ontario compared the effectiveness of one and two doses of the measles, mumps and rubella vaccine between September 2009 and June 2010. Similar outbreaks occurred in New York and New Jersey in the United States and Israel at the same time.

Of 134 people in Ontario with confirmed mumps, 72 percent were male, 59 percent were between 15 and 24 years of age, and of the 114 people who had available vaccination history, the majority – 72 percent – had received no vaccine or only one dose.

Those born between 1980 and 1994 were more likely than expected to become infected, especially those aged 15 to 24. “The clustering of cases, particularly among people born between 1985 and 1991, reflects the susceptible cohort,” Dr. Shelley Deeks of the Ontario Agency for Health Protection and Promotion, wrote. “In addition, the active social lifestyle of this age group may have the transmission of the disease. The predominance of male cases was likely due to the settings in which they were exposed to the virus. These settings included athletic events, such as hockey tournaments, where there is frequent close contact between people.”

A review of 50 mumps outbreaks showed that the effectiveness of one dose of the MMR vaccine ranged from 73 percent to 91 percent, compared with the effectiveness of two doses, which ranged from 91 percent to 95 percent. While mumps outbreaks in countries with two dose vaccination policies are typically unusual, they have become more frequent since 2006.

“Outbreaks of mumps in Canada and abroad serve as a reminder that we cannot become complacent about vaccination programs or maximizing vaccine coverage,” the authors wrote, according to the Canadian Medical Association Journal. “Closely monitoring waning immunity will help to ensure that we have the necessary data for making policy decisions, such as whether a third dose of MMR vaccine is necessary or whether a different vaccine should be considered, and for evaluating the cost-effectiveness of the program.”

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