There is a lot of confusion about what side effects are and are not. And there is a lot of disinformation about side effects. It is important to understand the facts and where to get credible information about vaccine side effects. 

When talking about vaccine side effects, you may hear the term “adverse event.” An adverse event is any unwanted thing that happens after vaccination. Some adverse events are truly caused by the vaccine (reactions) and others are just coincidences because they happen after receiving a vaccine.

These include:

• Side Effects: These are unwanted symptoms that are caused by the vaccine or the injection. The most common side effects are mild and usually go away on their own after a few days without any treatment. Common and mild side effects include redness and swelling where the vaccine was given or a low-grade fever.
• Serious Reactions: These include allergic reactions. Allergic reactions are very rare and will show up immediately after vaccination (usually within 30 minutes but no more than 4 hours).

Many people think that all adverse events following the vaccine are caused by the vaccine but that’s just not the case. Vaccines are some of the most studied medical treatments, so scientists have a very clear understanding of what is and is not related to vaccines. Just because one thing follows another does not mean that the first thing caused the other. For instance:

• Around 12 months: Most children take their first steps and get the MMR vaccine, but the MMR vaccine does not cause children to walk
• By 3 years old: Most children are potty trained and can usually name colors, but the ability to name colors has nothing to do with bladder control.
• By 5-6 years old: Most children can stand on 1 foot for 10 seconds and begin to read, but the ability to stand on one foot has nothing to do with the ability to read.
• By 21 years: Most men will reach their full height and can legally drink alcohol, but drinking doesn’t stop growth.

Autism is one of the conditions that some parents mistakenly relate to vaccination. Most autistic children will show symptoms of autism around 12 – 18 months of age, the same time as when they receive some vaccines. But we know through dozens of studies, involving hundreds of thousands of children, that vaccines do not cause autism.

Here is a summary of just some of the studies looking at vaccines and autism.

It is important to understand the science and know the facts to make informed decisions about your family’s health.

Side effects are unwanted but expected symptoms.

When talking about side effects, it is important to understand two things:

• Every medical treatment, including vaccination, has side effects
• Unwanted does not necessarily mean bad

In the case of vaccines, mild side effects often mean the vaccine is doing its job. Remember, a vaccine’s job is to train the immune system to recognize and defend against an invader. That is exactly what the body is doing when someone has a mild side effect to a vaccine, like tenderness or swelling where the vaccine was given. Other common, mild side effects include:

• Mild fever or chills
• Chills
• Feeling tired
• Headache
• Muscle and joint aches

Mild side effects usually go away on their own, without treatment, in a few hours to days.

Serious side effects are extremely rare. How rare?

For every million vaccine doses, only 1-2 people will have a serious allergic reaction – that is about 0.0002% of all the vaccines given.

By contrast, consider the risk of these vaccine-preventable diseases:

• Meningococcal: About 10-15% of people will die
• Hib: About 5% of people will die and about 15 – 20% of survivors will be deaf
• Tetanus: About 6% with mild tetanus and up to 60% with severe tetanus will die

Some parents are concerned about vaccination because there are risks associated with vaccination. But there are risks associated with everything in life. We cannot eliminate risks but we can make healthy choices by accurately understanding risks and benefits.

Choosing not to vaccinate doesn’t mean eliminating risk. It just means trading the minuscule risk of a serious side effect for the much greater risk of death or disability from a disease.