Doing well still needs to sell: Bringing vaccine-preventable diseases under further control in Canada requires a shift in thinking

“Vaccines, of one sort or another, have conferred immense benefit on mankind but, like aeroplanes and motor-cars, they have their dangers....It is for us, and for those who come after us, to see that the sword which vaccines and antisera have put into our hands is never allowed to tarnish through over-confidence, negligence, carelessness, or want of foresight on our part.”

Sir Graham S Wilson, The Hazard of Immunization, 1967 (discussing isolated incidents in early vaccine production)

In a recent paper, Gangarosa and colleagues (1) described the impact of antivaccination movements on the control of pertussis. They corroborated other analyses suggesting that once high vaccine uptake and herd immunity are attained, the perceptions of vaccine risk tend to take over and sway individuals and even sometimes governments away from immunization. In the example of pertussis, a disease that rivals measles and neonatal tetanus in impact in the developing world, the disease readily resurfaced in developed countries that lost confidence in the vaccine. In Japan, for example, two deaths alleged to have been caused diphtheria-pertussis-tetanus vaccine led to the official discontinuation of a national program. The outbreaks that followed were responsible for 41 deaths and at least 13,000 cases of the disease. What is even more unfortunate in this case and others – such as the recent decision in France to suspend hepatitis B vaccination in the school system (based on political pressure rather than science) – is the collaboration of governments in abandoning immunization.

Canada and other countries with successful immunization programs are walking a tightrope between achieving herd immunity through optimal coverage levels and slipping back because increasingly vocal and misinformed opponents of vaccination are able to get their message across (Figure 1). With diseases under improved control and vaccine coverage high (but not yet ideal), we are at risk of slippage. Surveys suggest that overall, only about 1% to 2% of the population is opposed to immunization, but at the same time, recent experiences with introducing new vaccination programs in Canada demonstrate the immediate impact of intense negative and misleading vaccine publicity. Parents in Manitoba who had signed consent for their children to be vaccinated against hepatitis B actually faxed the schools to revoke permission when misinformation was propagated through the media and directly to the schools just as the program was starting (personal communication). Although it is expected that the initial hepatitis B program coverage in Manitoba (estimated at 60%) will improve, such misinformation slows uptake and uses up valuable resources.

Figure 1).

Graphical relationship between disease incidence, vaccine coverage and reported vaccine side effects

The loss of confidence in vaccination programs can also occur when diseases are not under control. Introduction of a vaccine for varicella, a disease that affects 95% of the population by the time they reach the age of 20 years but that is unfortunately perceived by many to be a ‘benign’ disease, may be difficult. For this reason, it is important to maintain a flexible perspective on the incidence and morbidity associated with vaccine-preventable diseases so that we can counsel patients or their parents about the importance of being immunized even when disease incidence is low or improperly perceived as harmless. It is hoped that such counselling would also produce, as a spinoff, ‘antibodies’ (2) to counter future negative messages about vaccines that the patient or parent may encounter.

Although a direct comparison of pre- and postimmunization program disease rates has caveats, one thing is clear. Before vaccines, annual disease incidence rose and fell as susceptible populations built between outbreaks. Many who became infected suffered, such as those who developed paralytic polio or died from pertussis.

The numbers in Table 1 in the prevaccine years represent epidemic years, but because populations were universally susceptible, the risk of disease and disease morbidity and mortality was high and quite unpredictable. These days, we still see cycling but to a much smaller extent because the disease risk has greatly diminished due to high vaccine uptakes (Table 1). What has increased, however, are the reported cases of adverse reactions to vaccines, because before vaccination programs, there were none. This vaccine-induced morbidity is minuscule compared with disease morbidity, whether one considers the serious or minor reported cases. We have, however, entered a stage when these comparisons are legitimately being made and questions are being asked. These questions lead to inappropriate comparisons best illustrated by the last line in Table 1, eg, a simplistically crude comparison of adverse vaccine events compared with reported cases of vaccine-preventable disease.

TABLE 1:

Change in disease incidence after immunization program implementation

Disease		Prevaccine ‘era’ (maximum reported* cases)	Postvaccination (reported cases)			Percentage change (average)
			1996	1997	1998†
Polio		5300 (1953)	0	0	0	–100
Diphtheria		9000 (1929)	0	1	0	–99.9
Pertussis		20,000 (1940)	5408	4379	5311	–74.8
Tetanus		19 (1961)	0	0	0	–100
Haemophilus influenzae type b (Hib)		646 (1988)	55	66	40	–91.7
Measles		83,000 (1935)	335	572	15	–99.6
Mumps		52,000 (1942)	313	264	81	–99.6
Rubella		69,000 (1936)	302	4006	62	–97.9
Reported adverse events‡	’Minor’	0	6601	4615	3431	–
	’Serious’§	0	224	194	113	–

^*There is variable under-reporting of these diseases, for example, there are estimates of measles incidence of greater than 300,000 in some years, 2000 cases of Hib disease and 20,000 cases of polio;

^†Provisional data;

^‡Causality between the adverse event and vaccination is not required for inclusion;

^§Meeting criteria for advisory committee review (4) including cases requiring hospitalization, that are fatal or meet certain event categories

The fragile nature of trust is such that once destroyed by concerns about vaccine safety – even those that are unproven as has happened in France – the impact on immunization coverage can be profound and difficult to counter. Recovery of confidence can take years. It is precisely because vaccine safety is so vital and trust so fragile that enhanced monitoring programs specifically for vaccines beyond those in place to monitor other drug products on the market have been put in place in Canada. These include the active, paediatric hospital-based surveillance system known as IMPACT (3) as well as an expert advisory committee (Advisory Committee on Causality Assessment) charged with evaluating all reports of serious adverse events (4). These work together in concert with the passive reporting system, and alongside the National Advisory Committee on Immunization who issues recommendations on the use of vaccines in Canada. There is also extensive collaboration with partners around the world so that vaccine safety surveillance can be maximized. Should any signals be identified that require action, additional studies are conducted and/or program adjustments are made. A good example is the replacement of the live oral polio vaccine (OPV) with inactivated polio vaccine, thus eliminating even the rare case of vaccine-associated paralysis caused by OPV.

Today in the late 1990s, it is paradoxical that as health professionals, we are actually beginning to express a concern about the impact of the low incidence of disease. The concern is that, as these diseases are fading from memory, and a population of patients and practitioners emerges who have no experience with their devastating consequences, efforts to prevent them will relax. There is a concern that should some diseases reappear, they will not be recognized quickly and will spread before control measures can be put in place. There is a concern that some diseases previously acquired in infancy with reduced risk of morbidity (such as varicella), if not properly controlled by vaccination, may then shift the burden of illness into adult populations where infection has more complications.

Inexperience and unfamiliarity with vaccine-preventible diseases may lead to complacency that may grow into apathy. Apathy then leads to neglect, and neglect into failure to immunize. In the absence of societal intervention, underimmunization leads to a build-up of susceptibles, which primes a community for an outbreak of the disease as happened in Japan with pertussis. Complete immunization coverage, even in the absence of disease, is conceptually an easy pill to prescribe. Unfortunately, it is a bitter pill to swallow for those who believe antivaccination messages. But in the end, in a just society, it is the only way. The questions that we have to ask ourselves, and our patients and their parents are really the following. What are we more comfortable with and what do we want? Is it a return to the days when susceptibility to disease was universal, and every member of society ‘risked’ illness or even death? Or do we prefer the current situation, a universal immunization with a product that cannot be completely safe but has proven to be extremely safe when given on a controlled schedule? If we indeed prefer the latter, we must educate the public to stop considering the risks of vaccine against the risk of disease today, but consider instead the risks of vaccine today compared with the risks of disease yesterday. Experience has shown that if we stop vaccinating before total eradication, diseases return. And for some diseases such as tetanus, which has no herd immunity, it is only vaccination that is protecting us and our infants – who are at risk with a mortality rate from neonatal tetanus approaching 60%. As Phyllis Freeman (5) pointed out, “The very biology of vaccines makes the choice to employ them far more than a collection of individual decisions...The study of vaccine adverse events is not an effort to provide individuals with a basis for deciding whether to vaccinate but rather an effort to improve the safety and effectiveness of vaccines...It will be far easier to achieve herd immunity when risks associated with vaccines are known to be so small that public confidence in the safety of vaccines is secure.”