"The problem we face as pediatricians is that most developmental problems in children show up at the times when the children are most likely to be getting vaccinations. It's awfully hard to convince parents that there isn't a connection," says Davies, a member of the infectious diseases and immunization committee of the Canadian Pediatrics Society. The father of a 15-month-old boy, Davies learned about the autistic case from a colleague in Nova Scotia.

More and more parents are seeing supposed connections that tip the risk-benefit scales against vaccination. As many as 1 in 20 Canadian families is currently choosing to not vaccinate their children against serious infectious diseases such as the MMR trio as well as polio, diphtheria, whooping cough, tetanus and Hib, a bacterial infection responsible for meningitis and other infections.

That 5 per cent may be double the past level of vaccination objectors. Others are also missing complete vaccination for different reasons, such as a doctor's decision where allergies are involved. In Toronto, the non-vaccination rate could be as high as 9 per cent, according to one estimate submitted to the Canadian Institutes of Health Research, the federal funding agency.

"Parents are caught in the middle between people saying vaccination is the best thing they can do for their child and others saying vaccination is dangerous," says Dr. Kumanan Wilson, a University of Toronto professor of medicine.

Working closely with the Canadian College of Naturopathic Medicine, Wilson is directing the first scientifically based look in Canada at the emerging debate about childhood vaccination, a $150,000, two-year project that is focusing especially on the controversies over the MMR and influenza vaccines.

Wilson says studies elsewhere suggest that parent's no-vaccination decisions aren't based solely on personal interpretation of the medical pros and cons. Religious beliefs can play a part as can distrust of official pronouncements in the wake of public health failures like Canada's tainted blood scandal or Britain's mad cow disease in humans.

There are also strong indications that chiropractic and alternative medical options like homeopathy and naturopathy either harbour anti-vaccination attitudes or have been infiltrated by anti-vaccination campaigners.

A survey at the Canadian Memorial Chiropractic College in Toronto found only 5 per cent of first-year students said they were against vaccination while 30 per cent of fourth-year students were. The students picked up their anti-vaccination attitudes outside the classroom, said a report in the Canadian Medical Association Journal, including professional trade magazines containing "pseudoscientific articles ... based on outdated or non-existent data."

Evidence that senior chiropractic students lack critical thinking skills may be disconcerting but, says Heather Boon, it doesn't necessarily translate into public anti-vaccination attitudes.

"Even if they're not recommending vaccination to their patients, we don't know if that's much of a factor in their patients' decisions," says Boon, the alternative medicine expert on the research team and a pharmacy professor at the University of Toronto.

The researchers will try to unravel just how people decide through focus groups with parents from both sides, says Wilson.

The study is also going to try to test the most common explanation from doctors and public health officials for a decline in vaccination rates — that vaccines are victims of their own success. Because today's parents grew up in a country free of the scourge of polio and when mumps and measles didn't visit every block, the argument runs, they fixate on the relatively minor health risks from vaccines rather than the much larger risks if the infections returned.

For instance, just one in 100,000 children vaccinated against measles, mumps and rubella develop high fevers or some temporary loss of consciousness. But 10 per cent of children who got measles (400,000 a year at one time) suffered complications such as bronchopneumonia and serious ear infections. One in 1,000 developed encephalitis with 10 per cent of those dying.

And as long as measles exists somewhere in the world, it can be reintroduced here by something as simple as a Canadian sitting near someone on an airplane who is incubating measles.

"Our neighbourhood is a lot bigger in this day and age," says Dr. Judith Shindman of the medical affairs section of vaccine manufacturer Aventis Pasteur.

Yet coming to an informed decision on the medical aspects isn't all that straightforward either. Anti-vaccine information abounds, especially on the Internet, but an informal survey by The Star found that much of it is anecdotal and scientifically hit-and-miss.

A more rigorous investigation of 100 anti-vaccination Web sites around the world published last month by public health researchers in Australia found that one-third of the sites promoted themselves as sources for non-partisan information on both sides of the debate. But only 15 per cent contained anything supporting vaccination.

One in four of the anti-vaccination Web sites implied a bogus official status and most supported the scientific validity of their claims by quoting from self-published works, letters to newspapers or the alternative medicine movement. When research from established medical journals was quoted, the conclusions drawn were often inconsistent with those of the original authors.

"Overall this produced a spectre of the existence of masses of data on the dangers of vaccination," concluded the report in the Archives of Disease in Childhood.

But the official side of the story from vaccine makers, doctors and government is either so dumbed-down or so highly technical that it's also not terribly helpful to perplexed parents. The only portion of the official Canadian Immunization Guide easily understood by non-specialists is buried on page 42, under the heading "Talking with Patients About Immunization."

As well, getting detailed information from the federal health department can be a trial, although this may be related to the severe understaffing and underfunding in immunization areas. One concerned mother seeking the reports of adverse reactions to specific vaccine lots was initially asked to pay $1,200 in advance to compensate for time extracting the information from the department's antiquated non-computerized records.

Some factions on both sides are also prone to sensational exaggeration. In her best-selling book The Medical Mafia, since-disbarred Quebec doctor Guylaine Lanctôt, a fierce anti-vaccine campaigner, wrote: "The vaccinated child is a contaminated child."

Not quite in the same category but still overblown is the vaccine claim currently being made by the Community Health Department of Waterloo Region. In a pamphlet for parents, the officials say that the free shot against hepatitis B for Grade 7 students to be given as part of an Ontario-wide program confers "life-long immunity."

But the product monograph from Merck Frosst Canada states that duration of protection is "unknown" and the Canadian Immunization Guide simply states that 15 years' protection has been demonstrated for the vaccine.

The vaccination debate also abounds in myths. Most persistent among the anti faction is the belief that vaccine manufacturers are greedy exploiters hauling in profits by the bag-full.

Yet potential vaccine sales worldwide have been estimated at $6.5 billion, roughly equal to the sales of one successful ulcer drug. The number of companies producing vaccines in the U.S. has dropped from 37 to 10 since 1967, with a similar contraction in Europe.

Equally powerful among antis is a belief that the "authorities" have regularly said that vaccines are 100 per cent safe, only to be forced to backtrack later when problems emerged. No doubt there are occasional overblown claims like those of community health officials in Waterloo, but The Star unearthed no claims of 100 per cent safety in a week-long search through official Canadian and U.S. federal government vaccine material.

The deluge of myths, disinformation and misinformation in the vaccination wars is so great that it has obscured the clear evidence that immunization is without doubt the most beneficial medical intervention of all time in terms of lives saves and illness averted. The evidence is equally clear that any vaccination carries health risks — including even death in rare cases — but that the health risks from being unvaccinated and getting infected by measles, mumps, polio and the rest are many, many times greater.

These basic points are driven home by piles of peer-reviewed studies, the "gold standard" of scientific research, and by tragic real-life experiments such as those which took place in Britain, Sweden and Japan in the 1970s and 1980s.

Spooked by a public outcry from misinformation that linked whole cell pertussis vaccine to encephalopathy and sudden infant death syndrome, the health authorities in those three countries cut back on vaccination, sparking a dramatic upsurge in whooping cough.

From 1976 to 1988, Britain experienced three epidemics with more than 300,000 cases of pertussis and at least 70 deaths, half in a single year. In Japan, pertussis increased from 393 cases and no deaths in 1974, to 13,000 cases and 41 deaths in 1979, and in Sweden pertussis infection rates soared from 700 cases per 100,000 population in 1981 to 3,200 in 1984.

When vaccination was re-introduced, pertussis cases plunged.

Health Canada doesn't have up-to-date statistics on the extent of the anti-vaccination backlash, even though the federal department is responsible for licensing vaccines, monitoring safety at national level and issuing guidelines to doctors. Health Canada does not collect reports from the provinces on how many children entering school aren't vaccinated under the allowable medical, religious and "conscience" exemptions.

Health officials are planning a telephone survey sometime this year to ask parents about their children's vaccinations. That survey will update a study four years ago which found that 96 per cent of children two years or younger were reported as having received at least one MMR jab. In some provinces, the second injection isn't given until between ages 4 and 5.

Despite lacking statistical proof, federal and provincial officials, pediatricians and public health experts are all acting as if vaccination rates are sinking in Canada.

A high-level conference on vaccine safety, held behind closed doors in November, 2000, concluded that eroding public confidence had to be shored up by a putting into place by 2005 a national compensation scheme for vaccine injury.

The conference report, made public only a year afterwards, also strongly urged a guaranteed $500,000 budget for immunization safety research inside Health Canada and the creation of a private foundation for immunization research by April this year. There has been no sign of progress on any of those three items nor most of the 45 other conference recommendations.

At the core of these recommendations — and the aspect most often mentioned in The Star's interviews — is the urgent need to improve how knowledge about vaccines is transmitted to concerned parents and the general public.

"Timely responses to emerging safety concerns must be operating and visible to the public. Immunization opponents and their messages should be engaged so that they and the public are aware that criticisms are heard, investigated and responded to," says the conference report.

The case of MMR and autism demonstrates just how difficult that communications job is going to be.

The Nova Scotia parents who made the heartbreak choice almost certainly heard about a 1998 British report from a gastroenterology clinic in London. A dozen children who had become autistic and also developed bowel problems were sent to the clinic. Through after-the-fact interviews with parents or physicians, the clinic hypothesized a link between MMR vaccination and autism.

Such case-series studies are the ground floor of epidemiological investigations and have to be confirmed by much more rigorous work involving control groups. Yet five further investigations that looked at much larger groups, called population-based studies, found no evidence of a link between MMR vaccination and either autism or the inflammatory bowel disease.

Exhaustive reviews by the U.S. Institute of Medicine and by specialists in the Population and Public Health Branch of Health Canada both concluded that the whole body of evidence simply did not support a causal connection between MMR vaccination and autism.

The U.S. report, however, went on to say that it was impossible to rule out the possibility that MMR could contribute to autism in individual cases, although there was no link at a population-wide level. This caveat was understood by scientists. It merely recognized the statistical fact that the epidemiological studies weren't large enough to conclusively rule out an extremely rare event.

And since most countries where such investigations could be done already have MMR vaccination coverage of 90 per cent or better, looking for differences in autism rates between matched populations of vaccinated and unvaccinated children is extremely challenging, if not impossible.

Yet despite the overwhelming rejection of a causal link between MMR vaccination and autism, anti-vaccination groups have seized upon that statistical caveat to justify continuing doubts about the safety of the vaccine.

Some skepticism has been warranted in the past. Vaccination critics long complained about the high rate of temporary side effects like fever, crying, inflammation and worrisome convulsions from the early form of pertussis vaccine which used whole cells. The newest acellular formulation, included in the five-in-one shot most children get, has reduced convulsions by as much as 80 per cent.

Critics also pushed hard to have thimerosal, a mercury-based preservative, taken out of the most commonly used vaccines. They stepped up that pressure after the U.S. Public Health Service and the American Academy of Pediatrics jointly called in July, 1999 for thimerosal's removal from all vaccines used for infants and children.

Responding to that pressure, manufacturers reformulated their products perhaps more quickly than would otherwise have occurred. So Canadian infants are now not being exposed to thimerosal in the three routine vaccinations that occur by six months of age.

There are other such clouds, such as the contamination of polio vaccine in the 1950s and 1960s with a monkey virus that has now been linked to a rise in cases of three rare cancers. How effectively immunization officials respond to each such challenge will have a major effect on which way the scales of public support for vaccination tip.

For instance, a report on the thimersol affair from the U.S. Institute of Medicine last October contained a veiled reference to the fallout from what some saw as foot-dragging and a lack of sufficient concern at official levels. "The presence of mercury in some vaccines can raise doubts about the entire system of ensuring vaccine safety, and late recognition of the potential risk of thimersol in vaccines may contribute to a perception among some that careful attention to vaccine components has been lacking."

The thimersol review by Health Canada also noted that the stakes were high. "In part, media and public concern about thimersol likely reflects increasing public intolerance of avoidable exposures of children to real or even theoretical risks from all sources."

But, as Calgary pediatrician Dele Davies reminds a listener: "People forget that scientists have families as well. No one wants to be recommending things that wouldn't be safe for their own children."