May 18, 2011
Double Dose Of Vaccine Helps Reduce Mumps Outbreaks
After an analysis of a recent mumps outbreak in Ontario, Canada, researchers express the importance of receiving the recommended two doses of measles-mumps-rubella (MMR) to ensure adolescents and young adults are well protected from the trio of diseases.
A team of researchers from the Ontario Agency for Health Protection and Promotion, the University of Toronto, the Ontario Ministry of Health and Long-term Care, and the North Bay Regional Health Unit in Ontario compared the effectiveness of one and two doses of the MMR vaccine during the mumps outbreak in Ontario between September 2009 and June 2010.
The study showed that nearly three-quarters of those affected with the mumps had received no shot or only one dose.
Of 134 people in Ontario with confirmed cases of mumps, 72 percent were male and 59 percent were between 15 and 24 years old. Vaccination history was available for 84 percent of confirmed cases; the majority of those people -- 72 percent -- had no or only one dose.
Many people in the 15-24 age group would not have gotten a second MMR dose, which was not recommended in Canada until 1996. And compared with older adults, they would have more chances to be exposed to mumps, particularly those living in college dorms.
The findings underline the importance of having children get two doses of the vaccine, said lead researcher Dr. Shelley L Deeks of the Ontario Agency for Health Protection and Promotion in Toronto.
"We need to ensure that older adolescents and young adults are up-to-date with their second dose, especially before they go to university," Deeks told Reuters Health.
"The clustering of cases, particularly among people born between 1985 and 1991, reflects the susceptible cohort," writes Deeks and colleagues. "In addition, the active social lifestyle of this age group may have facilitated 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."
Outbreaks of mumps are rare in countries with two-dose vaccination policies, although they have become more frequent since 2006. People only eligible for a single dose and low vaccine coverage are some of the possible reasons for the resurgence of mumps in developed countries.
The study authors suggest that as two-dose MMR programs have been in place in Canada for about 14 years, there could exist the impact of waning immunity among recipients of two doses of the vaccine.
"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 said.
"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," they added.
Mumps is a viral infection that causes fever, headache, muscle aches and swollen glands around the jaw. Most people recover in a few weeks, but a small number of patients can have serious complications, such as an inflammation of the brain that can be life-threatening, or possible hearing damage, or painful inflammation of the testicles or ovaries.
Similar mumps outbreaks occurred in the United States (New York and New Jersey) and Israel at the same time as the Ontario outbreak, where cases were seen predominantly among males and those who had received at least one dose of the MMR vaccine.
When MMR became available in the 1970s, US and Canadian officials began recommending a single dose of the vaccine to protect children against mumps, measles and rubella. But after outbreaks in the 1980s, US health officials added a second MMR dose in 1989 for children 4 to 6 years old. Canada introduced a second dose in 1996.
In recent years, there have been mumps outbreaks in the US, Canada and other countries -- and some of those outbreaks have included people who have had two doses of MMR.
"No vaccine is 100-percent effective," said Deeks. Many researchers suspect that the vaccine's protective effect may start to wear off as the years ware on, leaving some people vulnerable.
Based on cases in the Ontario mumps outbreak, Deeks and colleagues estimated the effectiveness of two-dose MMR at between 66 and 88 percent, depending on the age group. That was higher than the effectiveness of one dose, which ranged from 49 to 81 percent.
Deeks said the findings were "reassuring" because two-dose MMR was more effective -- and because none of the people who got sick during the outbreak were young children.
It is unclear exactly how long mumps protection lasts with two-dose MMR. Based on the recent outbreaks that had affected older teens and young adults who did have two doses of MMR, some experts have suggested a third dose may be needed.
Deeks said for now it is important that teens and young adults who have not had a second shot get one.
Even if a vaccine is not 100 percent effective, vaccinating enough people can still prevent large outbreaks.
Deeks said it's important that health officials and the public not become "complacent" about mumps. "All children absolutely should receive two doses of MMR, and keep up with all their vaccines" she said.
The research team did not address the cost of the vaccine in their study report. In Canada, which has universal healthcare, parents don't have to pay for the shots for their children. But in the US, the price of each shot for families without health insurance ranges from $65 to $100, depending on where the shot is given.
Some doctors in the US do not offer certain vaccines because of their costs, and many insurance companies don't cover the cost sufficiently.
Some parents have also not allowed their children to receive the MMR shots out of fear that the vaccine is linked to autism. However, numerous studies have found no evidence that the vaccine contributes to autism.
One of the researchers who worked with Deeks on the study has received research funds from GlaxoSmithKline, one of the companies that makes the MMR vaccine.
The findings of the report from Deeks and her colleagues appears in the Canadian Medical Association Journal.
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