Vaccine Safety

Frequently Asked Questions

The questions and answers that follow are intended to assist in counselling about immunization; the wording and style are targeted at a general audience.

1. Do vaccines work?
2. Are vaccines safe?
3. How are vaccines made and licensed in Canada?
4. What would happen if we stopped immunizing?
5. Why do we still need vaccines if the diseases they prevent have disappeared from our part of the world?
6. Why can't I take a chance that my child won't get sick, as long as most other people are vaccinated?
7. Do vaccines weaken the immune system?
8. Can giving a child several vaccines at the same time overload the immune system?
9. Can natural infection or a healthy lifestyle be effective alternatives to vaccines?
10. Why do we need vaccines if we have better hygiene and sanitation to help prevent disease in Canada?
11. What about reports that vaccines are linked to chronic diseases or problems such as sudden infant death syndrome (SIDS)?
12. Do vaccines contain toxic ingredients?
13. Can vaccines transmit animal disease to people?
14. Is immunization compulsory in Canada? Does my child have to be immunized?

Question 1: Do vaccines work?

Answer: Yes. Vaccines work very well in preventing specific diseases. They are so effective that most of the diseases they prevent are now rare in Canada. Some people do not develop full immunity after being vaccinated. This is why some immunization programs include a second or third dose of a vaccine. For some diseases, we need "booster" doses because the protection of the vaccine wears off over time. However, no vaccine will work for 100% of the people who receive it. How often a vaccine might fail to work varies with each type of vaccine and each vaccine product. For more details, please see the chapters on specific vaccines in the Canadian Immunization Guide, 7th Edition 2006. Some vaccines also work by creating "herd immunity". When most people in a community have received a vaccine for a particular disease, the chance of an outbreak of that disease is greatly reduced. This "herd immunity" protects the small number of people who cannot be immunized for medical reasons or for whom the vaccine did not work. For herd immunity to be effective, however, as many people as possible must be vaccinated.

Question 2: Are vaccines safe?

Answer: Yes. Vaccines are among the safest tools of modern medicine. Serious side effects are rare. For example, severe allergic reactions can occur, but they very rarely do. In Canada, this kind of reaction has occurred less than once in every 1 million doses of vaccine, and there are effective treatments for this condition. The dangers of vaccine-preventable diseases are many times greater than the risks of a serious adverse reaction to the vaccine. For information on who should not receive specific vaccines, please see the Contraindications and Precautions section of each vaccine chapter in the Canadian Immunization Guide, 7th Edition 2006. Minor side effects from vaccines, on the other hand, are common. Many patients get a mild fever after immunization or soreness where they receive the injection. These reactions are a nuisance but do not usually last long. They can be part of the body's normal response to the vaccine.

No one in the field of public health takes the safety of vaccines for granted. Vaccine safety is an international concern. Information on possible safety concerns is communicated very rapidly among different countries. This careful monitoring ensures that public health authorities can act quickly to address concerns. In addition, research continues to improve vaccines.

Some examples follow:

• In 1999, some babies in the U.S. developed a rare form of bowel obstruction after receiving a new vaccine to prevent rotavirus infection (a cause of diarrhea, sometimes severe, in infants). Pre-licence studies had suggested that there might be an increased risk of this condition, and monitoring effectively picked up the problem. (In the first 1.5 million doses of rotavirus vaccine, 15 cases of bowel obstruction were reported.) Use of this vaccine was stopped in the U.S., and the manufacturer withdrew its request to license the vaccine in Canada.
• The oral polio vaccine (OPV), introduced in the 1950s, prevented hundreds of thousands of polio cases. It was also found to cause a form of paralysis once in every 3 million doses. A vaccine that uses inactivated virus (IPV) is now used almost exclusively throughout the world and cannot cause even this rare adverse event.
• The original whole-cell pertussis (whooping cough) vaccine sometimes caused high fever, seizures or collapse. A vaccine was developed that uses only part of the cell of the pertussis bacterium. This vaccine has fewer side effects and is now used instead.

In considering the safety of vaccines, it is important to look at both risks and benefits. If there were no benefit from a vaccine, even one serious side effect in a million doses could not be justified. If there were no vaccines, however, there would be many more cases of disease, more serious side effects from disease, and more deaths.

The examples from countries that have stopped or decreased their immunization programs have illustrated this fact many times in recent years. The diseases we can prevent with vaccines can lead to pneumonia, deafness, brain damage, heart problems, blindness and paralysis in children who are not protected. We are fortunate in Canada to have vaccines for diseases that still kill and disable children throughout the world every day. The risks of not getting immunized are a lot greater than any risk of immunization itself.

Question 3: How are vaccines made and licensed in Canada?

Answer: Vaccines for humans are regulated in Canada by the Biologics and Genetic Therapeutics Directorate of Health Canada. Like all medicines, vaccines must undergo several stages of rigorous testing before they are approved for use. The Bureau also supervises all aspects of vaccine production by the manufacturers. Before any vaccine is licensed and approved for use in Canada, the factory where it is manufactured must be inspected to ensure that all stages of production meet the requirements for safety, sterility and quality control. Before release by the manufacturer, each batch of vaccine is tested for safety and quality under guidelines specified by the Biologics and Radiopharmaceuticals Evaluation Centre. Most safety tests are carried out by both the manufacturer and, independently, by the laboratory of the Bureau. Once vaccines are in use, Canada has several systems in place to ensure that they are carefully monitored and that any problems are dealt with quickly. These systems are described in the section "Adverse Events" in the Canadian Immunization Guide, 7th Edition 2006.

Question 4: What would happen if we stopped immunizing?

Answer: Experience from other countries shows that diseases quickly return when fewer people are immunized:

• Ireland saw measles soar to more than 1,200 cases in the year 2000, as compared with just 148 the previous year, because immunization rates fell to around 76%. Several children died in this outbreak.
• A large outbreak of rubella (German measles) occurred in Nebraska in 1999. All 83 cases in this outbreak involved adults who had not been immunized. Most of them came from countries where rubella immunization is not routine. The outbreak spread from a meat-packing plant to the general community, including several pregnant women and two day care centres. The greatest danger from rubella is to infants, who may be born with congenital rubella syndrome if their mothers are infected during pregnancy.
• In 1994, there were 5,000 deaths due to diphtheria in Russia after the organized immunization system was suspended. Previously, Russia (like Canada) had had only a few cases of diphtheria each year and no deaths. Diphtheria toxoid came into routine use in the 1930s, but even today diphtheria remains a severe disease. About one person in 10 with diphtheria still dies in spite of medical treatment.
• In the U.K., a major drop in rates of immunization against pertussis (whooping cough) in 1974 was followed by an epidemic of more than 100,000 cases and 36 deaths in 1978.
• Japan had 13,000 cases and 41 deaths from whooping cough in 1979, after only 30% of children received pertussis immunization. In earlier years, when most children received vaccine, Japan had only a few hundred cases of whooping cough and no deaths.
• Sweden had a similar experience with pertussis. When vaccination programs restarted, the number of cases fell once again.

Question 5: Why do we still need vaccines if the diseases they prevent have disappeared from our part of the world?

Answer: It is important to continue vaccine programs for four basic reasons:

• First, unless a disease has completely disappeared, there is a real risk that small outbreaks can turn into large epidemics if most of the community is not protected. The only disease that has been entirely eliminated in the world so far is smallpox. Some diseases, such as tetanus, are caused by bacteria that live naturally in the soil. The risk of diseases like tetanus will never disappear, so continued immunization is important.
• Second, no vaccine is 100% effective. There will always be some people who are not immune, even though they have had their shots. This small minority will be protected as long as people around them are immunized.
• Third, there are a small number of people who cannot receive vaccines. These may be people who have previously had a severe allergic reaction to a component of the vaccine, or they have a medical condition that makes receiving vaccines too risky for them. These people are not protected from disease, and for some diseases it is very important that people around them are immune and cannot pass disease along to them. By protecting themselves, immunized people can also protect those around them who are vulnerable to disease.
• And fourth, most vaccine-preventable diseases are still common in other parts of the world. Travellers can carry them from country to country. If we are not protected by immunization, these diseases will quickly spread. For example, most cases of measles in Canada today can be traced to someone who travelled here from a country where measles is more common.

Question 6: Why can't I take a chance that my child won't get sick, as long as most other people are vaccinated?

Answer: Unvaccinated children have a much greater chance of getting disease than children who have received the vaccine.

Two recent studies of disease outbreaks in the U.S. illustrate this concern. Children whose parents chose not to have them immunized against measles were 22 to 35 times more likely to get measles than were immunized children. Children who did not receive the vaccine for pertussis (whooping cough) were almost 6 times more likely to get whooping cough than immunized children; the risks were even higher for the younger children (children < 11 years old), who were 62 times more likely to get measles if they were not immunized and 16 times more likely to get pertussis in these outbreaks.

Unimmunized children also add to the risk for children who cannot receive vaccinations or for whom the vaccine did not provide full protection from disease. People who are not immunized can be carriers of disease and pose a risk to those around them, even if they do not get sick themselves.

Question 7: Do vaccines weaken the immune system?

Answer: No. Vaccines strengthen the immune system to protect children and adults from specific diseases. This is true even for newborn infants. Infants and children are exposed to many kinds of germs every day, through normal eating, drinking and playing. Scientists estimate the immune system can recognize and respond to hundreds of thousands, if not millions, of different organisms. The vaccines recommended for children and adults use only a small portion of the immune system's "memory". Infants need to be protected with vaccines because they are more likely to get very sick from the diseases that vaccines can prevent, such as diphtheria, whooping cough and meningitis due to Haemophilus influenzae type b (Hib). The recommended immunization schedule for infants in Canada is carefully timed to ensure that newborns and older babies get safe and effective protection from the diseases that are most likely to seriously harm them.

Question 8: Can giving a child several vaccines at the same time overload the immune system?

Answer: No. Only vaccines that have been shown to be safe and effective when given together are administered at the same time. When new vaccines go through the extensive testing process, they are given along with all of the recommended childhood vaccines. Scientific studies assess the effect of giving these vaccines at the same time.

Children may receive several vaccines during the same clinic visit, but only after studies have shown that this is a safe practice. In order to receive a licence to combine vaccines, the manufacturer must also prove that the combined product does not make any of the vaccine components less effective or raise new safety concerns. Giving several vaccines at one time keeps children safe by protecting them against more diseases sooner. As an added benefit, it also reduces children's discomfort by reducing the number of injections they receive, and it saves parents the time and expense of additional office visits.

Question 9: Can natural infection or a healthy lifestyle be effective alternatives to vaccines?

Answer: Vaccines create immunity to specific diseases without causing the suffering of the disease itself. Children do develop immunity to many different germs through their everyday exposure to these infections. However, the diseases we can prevent with vaccines kill and disable children. For some diseases (e.g. tetanus and meningitis) the vaccine creates stronger immunity than natural infection does. Boosting the immune system in general through herbs or vitamins does not offer specific protection from the viruses and bacteria that cause vaccine-preventable diseases. For infants, breast-feeding offers protection against some infections, such as colds, ear infections and diarrhea, because the infant receives immune-boosting proteins in the mother's milk. Despite its many benefits, however, breast-feeding does not protect infants from the specific diseases we can prevent with vaccines. Vaccines also use a natural mechanism to keep us healthy by taking advantage of our natural immune response. A vaccine stimulates antibodies so that if we are exposed to that specific virus or bacterium in the future, our immune system can mount an effective attack.

Question 10: Why do we need vaccines if we have better hygiene and sanitation to help prevent disease in Canada?

Answer: Better living conditions have been important in controlling some kinds of infectious diseases, such as diseases spread by dirty water. For the specific diseases that vaccines can prevent, however, disease rates only began to drop dramatically after the vaccines for those diseases were licensed and came into widespread use:

• Measles vaccine was first approved in Canada in 1963. Sanitation and living conditions in Canada have not changed greatly since that time. Before immunization, almost everyone got measles. For many children, the disease was serious: about 5,000 were hospitalized every year, and 50 to 75 children died. Today, because the vaccine is in wide use, there are few cases of measles in all of North and South America, including communities where living conditions are much poorer than in Canada.
• Meningitis (infection around the brain) and other severe infections due to Hib were common until just a few years ago. About one in every 300 Canadian children developed Hib disease by age 5. About 100 infants died each year from Hib meningitis, and many more suffered brain damage or deafness. Immunization against Hib became routine in the early 1990s. Since then, Hib disease has almost disappeared in Canada, from about 2,000 cases a year to less than four cases in the year 2000. Sanitation is no better now than it was in 1990, so it is hard to credit anything but the widespread use of Hib vaccine for this dramatic improvement.
• Many children in Canada still get very sick from pertussis (whooping cough) each year, and every year one child dies from this disease. Nearly all of the children affected got the disease because they were not immunized against pertussis.

Question 11: What about reports that vaccines are linked to chronic diseases or problems such as sudden infant death syndrome (SIDS)?

Answer: Vaccines are sometimes blamed for conditions that are poorly understood. A child's first year of life is a time of tremendous growth and development, and it is a time when serious problems may start to appear. It is also the time when most vaccines are given, but this does not mean that vaccines cause these problems. Many of our vaccines have been in use for decades with no evidence of long-term adverse effects. Still, research to ensure the safety of vaccines continues. Anti-vaccine books and web sites claim that vaccines cause autism, seizure disorders, multiple sclerosis (MS) or Crohn's disease, among other health problems. These connections have never held up to scientific scrutiny. Recent research using the best scientific methods and reviews of studies from around the world provide very strong evidence that

• MMR vaccine does not cause autism or inflammatory bowel disease.
• Hepatitis B vaccine does not cause multiple sclerosis or relapses of pre-existing MS.
• Pertussis vaccine does not cause brain damage.
• Childhood vaccines do not increase the risk of asthma.
• Vaccines do not cause SIDS. (Fortunately, we have learned that other factors, such as sleeping position and second-hand smoke, are linked with SIDS, and successful public education campaigns about these factors have helped to reduce the rate of SIDS in Canada.)

More extensive discussion of specific vaccine concerns is available in the resources for patients and parents listed in the Canadian Immunization Guide, 7th Edition 2006.

Question 12: Do vaccines contain toxic ingredients?

Answer: The main ingredient in most vaccines is the killed or weakened germ (virus or bacterium), which stimulates our immune system to recognize and prevent future disease. Some newer vaccines are made from only part of the germ's cell (for example, a purified sugar or a purified protein).

• In addition, vaccines usually contain sterile water or salt solution.
• Some vaccines are prepared with a preservative or antibiotic to prevent bacterial growth.
• Some vaccines also contain substances known as stabilizers, to help maintain quality during storage.
• Some vaccines contain an "adjuvant". These substances work to boost our immune response to the vaccine and make it more effective. The amount of any of these ingredients in a vaccine is extremely small, and every batch of vaccine is tested for safety and quality in Canada before it is released for public use.

A preservative called thimerosal received attention in the U.S. in 1999 because it contains mercury and it is used in some vaccines for children. As a precaution, U.S. authorities recommended that the use of vaccines containing thimerosal be reduced or eliminated. In 2001, an independent panel of the U.S. Institute of Medicine conducted an extensive review of this concern. The panel found no evidence that the amount of mercury in childhood vaccines causes damage to a child's nervous system. In Canada, the only routine vaccine for children that contained thimerosal was the hepatitis B vaccine. Canadian infants were never subject to the same level of mercury exposure from vaccines as U.S. infants. A new formula for hepatitis B vaccine, with no thimerosal, is now available. Meanwhile, research into whether thimerosal in vaccines is truly a risk to infants is continuing.

The ingredients for each vaccine in use in Canada is described in the specific vaccine chapters in the Canadian Immunization Guide, 7th Edition 2006.

Question 13: Can vaccines transmit animal disease to people?

Answer: Because vaccines are a natural product, they sometimes require the use of animal cells during production. This process is strictly controlled so that it does not pose a risk to people. No brain cells are used in manufacturing vaccines in Canada. During the manufacturing process, the vaccines are purified, and all animal cells are removed. However, each batch of vaccine is tested to ensure that it is free from infectious agents.

For some vaccines in Canada, material derived from cows (for example, gelatin and lactose) have been used in the manufacturing process, and this has raised the question of whether vaccines can transmit "mad cow disease" to humans. Scientists in several countries have studied this risk and estimated that, in theory, there could be a risk of one person in 40 billion being exposed to the disease through a vaccine. Even though the risk is extremely small, vaccine manufacturers are working to find alternatives to these components. Meanwhile, Canada is making sure that any vaccine ingredients derived from cows come only from countries that are free from mad cow disease.

Question 14: Is immunization compulsory in Canada? Does my child have to be immunized?

Answer: Immunization is not compulsory or "forced" in Canada, but we do have regulations that help ensure that as many people as possible are protected by vaccines from the diseases they prevent. Some provinces require certain vaccines to be given before a child can enter school, but these are not mandatory in the usual sense of the term. Rather, parents (or children, if they are old enough to give consent) are required to declare a choice of whether to have their child (or themselves) immunized or not. If they choose not to, the child may be told that he or she must stay home from school if there is an outbreak of disease. This rule is designed to keep unimmunized children from getting sick and to keep the outbreak from spreading. School entry regulations also give parents an opportunity to bring their child's immunizations up to date. Health care workers may also be required to have certain vaccinations, such as hepatitis B vaccine and an annual 'flu shot. If they refuse, they may be required to stay away from work during an outbreak. This practice protects their patients, who could be in grave danger if they became ill with a communicable disease.

Conclusion

Because the diseases that vaccines can prevent are so rarely seen by the general public today, it is understandable that vaccine safety concerns have such a high profile. Careful and timely counselling can help patients weigh the benefits of vaccines and the risks of disease, as well as the small risk of the vaccine itself. By providing vaccines in a climate of appropriate informed consent, including discussion of the common misconceptions that are circulating, immunization will maintain its status as one of the most effective preventive measures in the history of medicine.