Health

Check out our Immunization Schedule.

One summer, my mother wasn't allowed to go the park because of polio. She grew up in Windsor, Ontario, in an ivy-clad Tudor house opposite Memorial Park. Directly across the street was the park's snack bar, where she and her friends liked to go for ice cream. But during the polio outbreak of 1937 the snack bar, the playground a little further down the way and, most of all, the wading pool were strictly off limits. "My mother was terrified that I'd pick up germs from someone who had polio," she recalls today. "People were afraid to go swimming. They were afraid to go anywhere there was a crowd."

This generation of parents has never had to worry that their children will catch deadly diseases in the playground sandbox. We worry about car accidents, kidnappers and terrorism, but not polio. We may remember getting our polio shots, but the ravages of the disease itself - the children who died or were crippled for life - we have no recollection of those. We've forgotten that before the polio vaccine was introduced in the mid-1950s, there were several thousand cases in Canada each year. Happily, we don't remember diphtheria or tetanus either. We're not even sure what they look like. Chances are we've heard more about possible adverse reactions to vaccines than we've ever heard about the diseases they were designed to prevent.

When a child dies from whooping cough (pertussis), as a handful still do every year in Canada, it doesn't make the news. But when there's a speculative report of a link between a vaccine and autism, sudden infant death syndrome (SIDS) or asthma, it may end up on 60 Minutes. That's because, even though deadly and nasty diseases like polio, diphtheria and measles have been virtually eliminated since the introduction of widespread immunization, there's a small but vocal minority that still believes vaccines do more harm than good. The very fact we're engaged in this debate is arguably a luxury of living in a society where vaccinations have erased the memory of these dreadful illnesses that once killed thousands of Canadian children and devastated families.

One of the theories that fuelled anti-vaccine rhetoric in the 1970s blamed the diphtheria-pertussis-tetanus (DPT) vaccine for some cases of SIDS. It gained credence for a while due to claims - later proven to be false - that SIDS virtually disappeared in Japan after that country raised the starting immunization age from three months to two years in 1975. What actually happened was that people stopped making damage claims for DPT-caused sudden infant death, once the shot clearly could not be implicated. SIDS deaths continued during this period. What increased was infant deaths due to pertussis.

It's understandable that someone made this connection, since SIDS has confounded experts for years, and most SIDS deaths occur during the period when babies get three DPT needles. Therefore, it's likely that some SIDS babies will die not long after their last needle. But the proximity of the needle to the death proves nothing. In fact a study found that, if anything, babies who had died of SIDS were slightly less likely to have been vaccinated with DPT.

More recently, the media have reported a supposed link between autism and the measles-mumps-rubella (MMR) vaccine. Cases of autism seemed to be increasing at the same time immunization was on the rise. However, the only scientific data linking autism to the MMR vaccine is a 1998 study that involved just 12 children with autism who also had inflammatory bowel disease (IBD). The theory was that the MMR vaccine may be responsible for the IBD, which may lead to a decreased absorption of essential nutrients, which in turn may damage the brain and cause autism. This theory has never been substantiated. Subsequent studies in the UK and Sweden have found no evidence that the incidence of autism increased after MMR was introduced.

Ronald Gold, a retired Toronto paediatrician, author of the book Your Child's Best Shot and part-time consultant to vaccine manufacturers, dismisses the idea. "If measles itself doesn't cause autism, and that's never been shown to be the case, it seems very unlikely that the measles vaccine [a weakened version of the virus] would do that." However, the study got lots of publicity, partly because it was published in the prestigious medical journal The Lancet. What got less attention was the editor's note in the same issue, which pointed out the flaws in the researcher's methods.

Perhaps the scariest stories have been the ones linking immunization to brain damage. The vaccine that was implicated most often was the whole-cell DPT vaccine, used in Canada until 1997. The difficulty here is that, like SIDS and autism, some childhood brain or neurological problems appear out of the blue in the first 18 months of life, when a child is never far from his last needle. The cause is often undetermined, so immunization becomes the scapegoat. However, studies have not been able to prove a causal relationship between brain damage and vaccinations. In fact, one major British study estimated the risk of brain damage due to the DPT vaccine at one in 100,000, while the risk of brain damage from pertussis itself is one in 11,000. In other words, the chance of your child getting brain damage from the disease is nearly ten times greater than from the vaccine that prevents it.

Of course, those who are opposed to vaccines have their own studies to cite and, predictably, each side claims the other's studies are flawed. How can ordinary parents assess the scientific validity of these arguments? The short answer is we can't, but there is one significant Canadian court case that speaks to this matter.

In 1988, a couple sued two doctors and vaccine manufacturer Connaught Laboratories for neurological damage to their son, which they claimed was caused by the pertussis vaccine. The lawsuit failed and, in fact, Toronto lawyer Alan West, who represented Connaught, is not aware of any successful Canadian lawsuit against a vaccine manufacturer. That obviously does not disprove every claim of vaccine damage, but this case is instructive for several reasons. One is that it took place when concerns were at their peak, and before newer and better vaccines and adverse-reaction monitoring systems had been introduced. Second, since it was a civil case, the family did not have to prove definitively that the vaccine caused the damage, simply that it was more likely to have done so than not. That's a fairly low bar to get over. Finally, a large part of the testimony consisted of a parade of international scientists, presented by both sides, who engaged in what amounted to a thorough debate on the scientific evidence available at the time. And based on that input, Justice John Osler concluded not only that the vaccine did not cause the damage in this case, but that it was very unlikely ever to do so.

"We'll never be able to definitively prove that no vaccine anywhere ever caused brain damage or death," says Gold. "Science can never prove a negative. But the most reasonable scientific explanation is that, if there is a risk of brain damage from vaccines, it's so small that we can't measure it."

One reason that allegations of vaccine-caused brain damage seem credible, and have caused worry even to those parents who immunize their children, is that vaccines have been associated with febrile seizures - or more accurately, immunizations sometime cause fever, and fever (particularly in babies) occasionally causes febrile seizures. These seizures, however caused (most are unrelated to immunization), are alarming events that seem like they could either cause, or be a sign of, brain damage. However, several studies have shown that this is almost never true, unless there is an underlying neurological problem that makes the child prone to seizures in the first place. The New England Journal of Medicine published a paper on this subject last August. Researchers looked at medical records from 679,942 children and, while they did find a slightly increased incidence of febrile seizures shortly after DPT and MMR needles, a follow-up study found that these children were no more likely than others to have problems such as developmental or speech delays, or learning disabilities. (However, at least one Canadian newspaper, The Peterborough Examiner, accompanied its story on this report with the misleading headline: "Two vaccines linked to seizures.")

The news gets even better. That study looked at the old whole-cell pertussis vaccine, which, over the years caused more side effects than other vaccines and took the brunt of the blame for more serious problems. It hasn't been used in Canada since 1997. The new acellular vaccine causes considerably fewer seizures and other side effects. When provinces switched to the new vaccine, observers saw a marked and lasting reduction in febrile convulsions after the pertussis shots. In other words, the "bad old" vaccine, while it never posed any proven threat of brain damage, is gone.

Even though most claims by the anti-vaccine camp have been debunked, their activism has served a useful function. Public concern about immunization has spurred authorities to initiate closer monitoring of vaccine effectiveness and safety. And the results are reassuring. Wikke Walop, of Health Canada's Division of Immunization, says her department collects reports of adverse events sent in by health-care professionals and manufacturers. "If, for example, there was a cluster of reports about one vaccine, we would investigate to see if it was all one lot number, or if there might be a particular risk group involved. But very few issues of concern have actually arisen."

Another program called IMPACT (Immunization Monitoring Program ACTive) started in 1991 and examines medical records from 12 children's hospitals across Canada for serious problems associated with vaccinations. "Every child who is admitted to one of these hospitals with seizures or encephalitis is screened for a possible link to recent vaccination," explains paediatric infectious disease specialist David Scheifele, director of the Vaccine Evaluation Center at the University of British Columbia. "In 2000, there were four febrile seizures and three hypotonic episodes [similar to fainting] admitted to IMPACT centres after the new DTaP vaccine was given. All seven of those children recovered nicely. During the same year, there were 115 admissions for pertussis complications, resulting in one death." In fact, IMPACT monitoring has turned up more cases of serious complications from vaccine-preventable diseases (including flesh-eating disease, an extremely rare complication of chickenpox) than vaccine reactions.

Nonetheless, the anti-vaccine theories keep coming. A current one is that the increase in chronic disorders like asthma, allergies, hyperactivity and diabetes may be linked to the more widespread use of vaccines since the 1960s.

"The standard phrase you hear from vaccine proponents is that there are no scientific studies that show a link between vaccines and whatever. It sounds so comforting," says Gerry Bohemier, a Winnipeg chiropractor and anti-vaccine activist. "But what studies have been done to show the long-term safety of vaccines?" Bohemier would like to see a large-scale, long-term study in which some children would be immunized and others would get placebo inoculations. The children would be followed for 15 to 20 years to see if the immunized group had increased incidences of asthma, autism and other disorders. But Scheifele says this kind of study is unlikely to ever be done. "Vaccine critics always demand absolute proof that a vaccine is safe, knowing full well that obtaining such proof is a tall task requiring huge numbers of observations at prohibitive cost."

Many would argue that there would be a human cost as well, since half the children in the study would be denied the protection from disease that vaccines provide. Who would volunteer their kids for that? The overwhelming majority of Canadian parents want their children to be immunized. Although some families miss some of the early shots, by the time they are seven, it is estimated that 95 percent of Canadian children have received all of the standard immunizations. In a recent public opinion poll, 84 percent of parents rated their confidence that vaccines are beneficial at eight out of ten or better.

However, immunization, while strongly encouraged, is not mandatory in Canada. What about the reluctant minority? Do they matter?

Immunization and disease are both percentage games. Even prior to immunization, most people never got polio and, even though almost everyone got chickenpox, only one in a thousand suffered serious complications such as encephalitis. But science has no way of predicting who the unlucky ones will be, so in order to protect the few you have to immunize everybody. The more people who get immunized, the lower the incidence of diseases and the better the chance that the disease will be wiped out. (The world was declared smallpox-free in 1980 and experts project that polio immunization will be eliminated in Canada by 2005.)

So, on a societal basis, it matters very much that most people are immunized. On an individual case, it matters less. Widespread immunization provides some protection to even the unvaccinated through what is known as "herd immunity" - with so many vaccinated people, there are fewer cases of a given disease and therefore fewer people to catch it from. That's why people who refuse immunization can usually do so with impunity. But that only works as long as most of us vaccinate our kids because, as history has shown, a substantial drop in immunization opens a window that allows the disease to come back. In Japan, DPT immunization dropped from 85 percent in 1972 to 13.6 percent in 1976 after two children died suddenly within 24 hours of getting their DPT shot. Forty-one children died in the whooping cough outbreak of 1979, when 13,092 children were stricken with the disease (compared with 269 in 1972). Russia saw serious outbreaks of diphtheria in the early '90s after vaccination rates declined following the fall of the Soviet empire. However, that sort of information seldom gets the big media coverage given to reports of vaccine side effects.

None of this means that vaccines are perfect. There have been problems. In very rare cases (one in 800,000, according to Gold) the oral polio vaccine, also no longer used in Canada, causes the disease. A vaccine for rotavirus (a common cause of serious diarrhea in babies) was withdrawn from the US market when it was found that a small but troubling number of babies suffered serious intestinal obstructions, apparently as a result (it was never used in Canada). Nor are vaccines perfectly safe for all children (see "Needle Notes," p. 52).

No doubt the debate will continue and there will be enough claims and counterclaims to keep researchers busy for years. There will always be some new disease or other unexplained medical phenomenon to blame on vaccines. But physicians who have worked in the Third World, where vaccine-preventable diseases are still devastating, have a different perspective. One paediatrician I corresponded with displayed little patience with anti-vaccine talk. "When I worked in Africa, I saw children die almost every day from measles. I saw polio as well. There is a downside to every advance, but the downside of immunization is so small. We should embrace this one real place where medical science has done something wonderful."

Needle Notes

Vaccines are not for everyone. David Scheifele, director of the Vaccine Evaluation Center at the University of British Columbia, estimates that about one percent of Canadian children have medical reasons to avoid one or more vaccines, including kids with compromised immunity (cancer or other chronic diseases) or those who've had an allergic reaction (hives, wheezing, a drop in blood pressure, etc.) to a dose. People who are allergic to eggs should avoid the flu vaccine, but while it was once thought that children with egg allergies should avoid getting the MMR vaccine, studies have since shown that this is not the case.

"Each vaccine comes with a list of precautions and contraindications to its use," says Scheifele. "Vaccine providers are expected to know these and search for them in each child's history before giving a vaccination. Parents should report any adverse reaction and discuss it with the child's physician." Experts also recommend that vaccinations be postponed when children have moderate to severe illnesses, so as not to confuse the symptoms of the virus with a reaction to the vaccine.

Check out our Immunization Schedule.

Follow-up (March 2003)

Shot Scares
A year ago we wrote about harmful myths that have some parents shying away from immunizing their children (“Hot Shots,” March 2002). Since then, another vaccine scare story has been making the media rounds: concerns that thimerosal, a mercury-based preservative, might be linked to autism. While lawsuits have already been launched, studies have not delivered any conclusive evidence. Meanwhile, Today’s Parent readers should know that thimerosal is not used in vaccines routinely given to Canadian children. It was once a component of the DPT (diphtheria, pertussis, tetanus) and Haemophilus b (Hib) vaccines. But in 1992, a thimerosal-free formula combining these vaccines (plus inactivated polio) was adopted in all provinces except Manitoba, which switched in 1997. Thimerosal was never a part of the MMR (measles, mumps, rubella) vaccine.

March 2002