Frequently asked questions about vaccine safety

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Vaccine safety is complex, and many people have questions about it. This page answers frequently asked questions about vaccine safety. 

Is it safe to get more than one vaccine at the same time?

Yes. Getting more than one vaccine at the same time is safe and ensures you or your children are protected against serious diseases earlier rather than later. Research shows that routine childhood vaccines work just as well when they are given at the same visit as when they are given at separate visits, and that giving these vaccines at the same visit does not carry any additional safety risks.

Some people worry that getting multiple vaccines at the same time can overwhelm their baby’s immune system. Your baby’s immune system is amazing. From the day your baby is born, their immune system is constantly working to protect them against the thousands of germs (viruses and bacteria) that they are exposed to as part of daily life. Vaccines represent a much smaller challenge than this daily exposure, and even a combination vaccine is easy for your baby’s immune system to handle. In fact, scientists estimate that a baby’s immune system could theoretically handle thousands of vaccines even if they were given at the same time.

As one doctor put it, “Worrying about too many vaccines is like worrying about a thimble of water getting you wet when you are swimming in an ocean.”

Examine the evidence: Multiple vaccines do not overwhelm the immune system. 

Are combination vaccines safe?

Combination vaccines are safe. Combination vaccines take two or more vaccines that could be given individually and put them into a single injection so that children can get protection against several diseases with just one shot. The diphtheria, tetanus, pertussis, hepatitis B, polio, haemophilus influenzae type b (DTaP-HB-IPV-Hib) vaccine, and measles, mumps, rubella (MMR) vaccine are examples of combination vaccines. Before a combination vaccine is approved for use, studies must show that the combination vaccine is just as safe and effective as each of the individual vaccines given separately. Research shows that the side effects of combination vaccines are similar to those of the individual vaccines given separately. The vast majority of side effects are very mild, such as temporary pain and swelling at the injection site.

Are the ingredients in vaccines harmful?

No. You may have heard or read that some of the ingredients could be harmful. However, this is only true at very high doses, much higher than is contained in a vaccine. Any substance, even water, can be harmful at a high enough dose. There is no evidence that any of the ingredients in these small amounts can cause harm.

They have not been linked to any disease or illness, with the exception of very rare allergic reactions in people with hypersensitivity to an ingredient. Learn more about vaccine ingredients here

What about autism?

Many large studies have found that vaccines do not cause autism.

A number of good studies have compared the health of vaccinated and unvaccinated children over many years. They have found that unvaccinated children were just as likely to develop autism as vaccinated children.

It is not known exactly why some children develop autism. Current research suggests there are likely many causes, and that both genetics and environment likely play a role. Because children with autism are often diagnosed after the age when they receive some vaccines, this has led some people to think that vaccines cause autism. But just because one thing happens after another, it does not mean there is a link between them.

Much of the controversy around a possible link between the MMR vaccine and autism came from a single small study published in 1998. The study was found to be fraudulent and was withdrawn by the journal that published it. Many large scientific studies around the world have since been conducted and have found no link between the MMR vaccine and autism.

Examine the evidence: Vaccines do not cause autism. 

Is the vaccine riskier than the disease?

No. For almost everyone, the risks from the diseases are far greater than the risks from vaccines that prevent them. However, there are rare exceptions, such as individuals with serious allergies to some vaccine ingredients, or those who cannot receive live vaccines because of weak immune systems.

Vaccine-preventable diseases cause serious illness and complications such as pneumonia, deafness, brain damage, heart problems, blindness, and paralysis, and carry a risk of lifelong disability and death. In comparison, vaccines carry very small risks. The main risks associated with vaccines are side effects, which are almost always minor and temporary. Serious adverse events are very rare.

It’s important to remember that a choice not to vaccinate is not a risk-free choice. By not vaccinating, you are trading a small risk for a much more serious risk.  Learn more.

Examine the evidence: Serious side effects are extremely rare. 

Can the vaccine give me or my child the disease it’s supposed to prevent?

It isn’t possible for inactivated (killed) vaccines to cause disease. This is because a germ has to be alive to cause disease.

Some vaccines contain weakened live versions of the whole germ (such as Measles, Mumps, Rubella (MMR) vaccine, and chickenpox (varicella) vaccine). These weakened germs in live vaccines will not cause the disease in a person with a healthy immune system. However, live vaccines are not given to people with very weak immune systems as they may develop the disease the vaccine is meant to protect against. Your health care provider will make sure that you or your child can safely receive a live vaccine before administering it.

Date last reviewed: 
Tuesday, Mar 24, 2020