September 2, 2008
As B.C. fights mumps outbreak, research shows incidence of chickenpox in the U.S. dropped 90% in 10 years of universal shots
by Fiona Morrow
VANCOUVER -- As B.C. health officials continue to monitor a major outbreak of mumps in the Fraser Valley, a study released today shows how vaccinations for common childhood illnesses can make significant inroads into mortality and morbidity.
The study, published in Pediatrics, the journal of the American Academy of Pediatrics, looked at the impact of the chickenpox (varicella) vaccination program in the United States over the first 10 years from the program's inception.
In 1995, the United States became the first country to introduce a universal childhood varicella vaccination program. The vaccine is available for every child, regardless of ability to pay. Though laws vary from state to state, it is part of the immunization required before children enroll in public school (exceptions being those seeking exemption because of a compromised immune system or conflict with philosophical or religious beliefs).
The Centers for Disease Control and Prevention study found that by 2005, the incidence of chickenpox across the United States had dropped by 90 per cent. Hospitalizations for chickenpox-related illnesses declined 75 per cent, while there were 74 per cent fewer deaths from these illnesses in people younger than 50. Of those, the greatest reduction was seen among children aged 1 to 4 (92 per cent) and 5 to 9 (89 per cent). Inpatient and outpatient medical costs associated with chickenpox fell 74 per cent.
In Canada, vaccinations are offered on a suggested schedule, but are not mandatory. The chickenpox vaccine is available, but not offered as part of the routine schedule.Many parents, even those who vaccinate their children on schedule, consider some childhood illnesses relatively harmless.
In British Columbia, however, the recent mumps outbreak has highlighted how quickly a community can be compromised when vaccinations fall beneath certain levels, and how serious such outbreaks can be. There have been 191 reported cases of the disease since the outbreak began in a religious community in Chilliwack in February. The total numbers affected are thought to be much higher, as milder cases may not have been reported.
Half of the 191 known cases were in people who had never been immunized against mumps; one-quarter had received at least one shot, and the other quarter did not have vaccination records.
One person developed meningitis, nine suffered hearing loss and 26 had swollen testicles or ovaries. It is too early to know how many of those cases will result in permanent deafness or sterility.
Herd immunity, in which a community is protected from a disease because of the strength of the cumulative immunization, is disease-specific. For the chickenpox vaccine to be effective, there needs to be 80- to 85-per-cent uptake. To prevent a measles outbreak, 90 to 95 per cent of the population needs to be vaccinated; for mumps, that figure is 85 to 95 per cent.
As the mumps vaccine tends to be given as part of the MMR (measles, mumps and rubella) shot, it is reasonable to assume that the Fraser Valley community is unlikely to be protected against measles, a more dangerous disease, noted Reka Gustafson, Medical Health Officer for Vancouver Coastal Health.
"The rate of refusal to vaccinate on conscientious or religious grounds varies from region to region," she added. Though immunization rates across Vancouver are very high, communities that refuse vaccination can create pockets in which herd immunity drops rapidly. As there is no national vaccination registration program in Canada, no one can be sure how many compromised communities there are, or where they are located.
Though a register would help to track potential problem areas, there are no plans to introduce mandatory vaccinations.
"It's an important ethical question," Dr. Gustafson said. "In Canada, we maintain an individual's right to accept or not accept immunizations as the primary importance, though there are times when that changes. Unvaccinated children can be excluded [from] school if there is an outbreak of a preventable disease, so there are consequences to that choice," she said. "Whether or not that is a consequence with any impact will depend on the individual involved."
This article was found at:
http://www.theglobeandmail.com/servlet/story/LAC.20080902.LVACCINE02/TPStory/National
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