TORONTO - Almost a decade ago, measles was declared eradicated in the Americas, thanks to widespread vaccination efforts. But outbreaks in Quebec and several U.S. states show that Western Hemisphere countries are still not immune to the virus, which can be imported by travellers and quickly infect pools of the unprotected.
And the number of those vulnerable to measles may, in fact, be growing, as some parents choose not to vaccinate their children for a variety of reasons, among them fear of possible side-effects or a belief that measles and other infectious diseases are merely a benign rite of passage in childhood.
Quebec's outbreak, which began early this year and this week jumped to 330 confirmed and suspected cases, has been traced to a traveller from France, where uptake of the measles, mumps and rubella vaccine hovers around 60 per cent of the population -- far below the 90-plus per cent rate in Canada.
Information provided by Quebec health authorities shows most of those infected were unvaccinated or inadequately vaccinated, making them easy targets for the highly infectious virus, said Dr. John Spika of Canada's Public Health Agency.
While vaccination schedules vary across the country, many jurisdictions call for a first dose at 12 months old and a second before admission to elementary school.
"We're looking at a problem that is primarily in high schools," said Spika, director general of PHAC's Centre for Immunization and Respiratory Infectious Diseases. "Most of their cases, over 60 per cent, are between the ages of 10 and 19.
"The data that we have received would suggest that a high proportion of those high school-aged children may not have received any vaccine. Was it because they're Quebecers born and raised whose parents refused vaccine or did they immigrate to Quebec after the school-entry check and never received vaccine in their home country?"
What is known is that it takes two shots of the MMR vaccine to fully protect against measles. In 1995-96, before Canada moved to a two-shot schedule, there was a large outbreak that public health officials predicted would have risen to 20,000 cases if the second-dose program hadn't been introduced.
And Quebec's epidemic may not be an isolated occurrence in Canada, said Spika, noting that a small outbreak occurred in Vancouver during the 2010 Olympics, resulting from the importation of three different strains carried by overseas visitors to the Games. "The three strains spread and then died out because there weren't enough susceptibles," he said.
Cases could still pop up anywhere in the country, he said. "If measles got into an unimmunized or inadequately immunized group of kids, yes, that could happen."
Far from being a trivial disease, the respiratory infection marked by a widespread skin rash can result in often severe complications: ear infections that in some cases cause permanent hearing loss; potentially fatal pneumonia; and encephalitis, or inflammation of the brain, which can lead to life-long cognitive impairment or even death.
In fact, measles kills about 165,000 children a year worldwide, primarily in low-income countries.
While that number is still unacceptably high, infectious disease experts say it is a far cry from the 750,000 deaths reported in 2000, which predated a massive global immunization push.
So why would anyone hesitate to have their child vaccinated?
A study by the U.S. Centers for Disease Control, published this week by the journal Health Affairs, suggests parents have a number of concerns that undermine confidence in vaccines. In the authors' survey of parents, most reported at least one worry over immunization, including that children:
--Suffer physical pain from shots
--Get too many shots in one doctor's visit
--Have too many vaccines before age two
--Receive vaccines containing unsafe ingredients.
One of the most controversial issues related to the MMR vaccine is the fear that the inoculation can lead to autism spectrum disorder, despite repeated studies that have shown no causal link between the vaccine and the developmental disorder.
Over the last decade, there was a resurgence of measles -- and mumps -- due to a dramatic drop in vaccination rates in the United Kingdom and some other European countries following a 1998 paper in The Lancet that linked the MMR vaccine to autism.
The journal retracted the paper by Andrew Wakefield and colleagues in early 2010 after the data presented was discredited. An investigation published by the British Medical Journal in January showed that the research by Wakefield, who has been stripped of his licence to practise medicine in Britain, "was an elaborate fraud."
Yet vaccination rates have been slow to rebound in those countries, in part because some people continue to distrust the vaccine.
Dr. Heidi Larson, a senior lecturer at the London School for Hygiene and Tropical Medicine, suggests that part of the reason the notion about autism persists "is there's a very proactive group of parents who have autistic children or have neighbours who have autistic children and who are absolutely convinced that that's the cause of it.
"This is what they believe," said Larson, who published a study in The Lancet this week looking at the reasons behind an apparent loss of public confidence in vaccines.
"And I think we understand the power of belief," she said in an interview from London. "From a medical perspective you want to believe that if we've got the scientific evidence, that's enough. And it's just not enough for a lot of people."
"It's challenging, but I think the medical community needs to come to terms with the fact that it's not going to be resolved by giving better facts to each parent about who can benefit ... what's really important is that we change the way of interacting with those who are still vaccinating and make sure that they are confident and that their questions are being answered."
In his view, said Spika, the autism link has been "totally debunked," and the best way for parents to protect their children is to ensure that they've had two doses of the vaccine.
"The measles vaccine is quite safe and there's no reason why one shouldn't give the vaccine."
