Canada's Chief Public Health Officer is advising that all Canadian children, teens and young adults should be vaccinated with two doses of mumps vaccine to help prevent and control future outbreaks.

Dr. David Butler-Jones issued a statement Tuesday to change current mumps vaccination recommendations to two doses instead of one dose for children. In addition, his office is calling for two-dose mumps vaccinations for certain high-risk groups, including secondary and post-secondary students and health care workers who may be susceptible to the virus.

"Outbreaks do happen from time to time," Dr. Theresa Tamp, a member of the panel that made the recommendation, told CTV Newsnet.

"To raise the level of immunity in the population and help reduce the chances of getting more of these outbreaks, the committee has recommended that two doses be given to certain high-risk groups."

Since the 1990s, vaccinations programs in Canada have included two doses of the measles, mumps and rubella vaccine (MMR). But some adolescents and adults immunized prior to the introduction of the two-dose programs in 1996-97, may have received only one inoculation and may therefore be susceptible to the virus.

"Kids below the age of 12, or born after 1996, would have already received two doses if they received the combined mumps-measles-rubella combined vaccine," said Tamp from CTV's Toronto studio.

While cases of mumps have declined dramatically with the introduction of publicly-funded immunization programs in Canada, the disease has not been eradicated.

The illness, which causes salivary glands to swell, can be contracted by anyone who hasn't been immunized or already been infected. It is more serious in teens and young adults, who can develop meningitis, encephalitis, hearing loss and other complications.

The most recent outbreak, centred in Nova Scotia and New Brunswick with sporadic cases elsewhere in Canada, has been the largest in a decade and has involved almost 600 patients. The majority of cases (64 per cent) have occurred in persons aged 17-37 years, many of whom are college or university students.

Immunization status is known for 284 cases:

• 16 per cent were not immunized
• 75 per cent received one dose
• 9 per cent received two doses of mumps-containing vaccine

In light of this ongoing outbreak, all Canadian students returning to school this fall are being advised to ensure their vaccinations are up-to-date, including two doses of mumps-containing vaccine. Having a second dose will help protect those who are unvaccinated, those who experience vaccine failure and boost the immunity of those experiencing waning immunity.

Both Nova Scotia and New Brunswick have begun offering post-secondary and Grade 12 students a second dose of MMR vaccine as part of the provinces' response to the recent outbreak.

The only way to receive a mumps vaccination is to receive the combined measles, mumps, rubella vaccine. There is no single-component mumps vaccine available in Canada.

It is assumed that the majority of Canadians over the age of approximately 40 years have natural immunity through exposure to the mumps virus in widespread circulation prior to the introduction of mumps immunization programs.