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A Patient's Guide to Vaccines

Published on Apr 12, 2019 and last reviewed on Oct 10, 2019   -  3 min read



Vaccines strengthen the immune system against certain germs that can cause serious infections and even death.

A Patient's Guide to Vaccines

What Is the Immune System?

The immune system is the part of your body that fights off infections. It is made up of special proteins (antibodies), chemicals, and white blood cells. It protects you against harmful germs including bacteria, viruses, fungi, and parasites. The immune system learns to recognize and respond to germs through a process called an immune response. A vaccine strengthens the immune system against certain germs that can cause serious infections and even death.

What Is a Vaccine?

A vaccine is a medicine that boosts your immunity against harmful germs and greatly reduces your risk of contracting a serious infection. They contain a weakened version of the germ that causes infection. When the immune system is exposed to the vaccine, it generates an immune response. So if you are ever exposed to that germ again, your immune system will be able to fight it off so that you will not get sick. Vaccines are also referred to as vaccinations, immunizations, shots or needles.

How Is a Vaccine Administered?

For children aged 3 and older, most vaccines are injected into the deltoid muscle in the shoulder (intramuscular). For children under the age of 3, vaccines are commonly injected into the thigh muscle. Some vaccines are injected right beneath the skin (subcutaneous) or administered by mouth (oral). The only vaccine that is given through the nose is the live attenuated influenza vaccine (intranasal).

What Types of Vaccines Exist?

There are 4 types of vaccines.

1. Live-attenuated vaccines contain a weakened (or attenuated) version of the germ that causes an infection. These vaccines can provide lifetime protection with just 1 or 2 doses. Examples include MMR (measles, mumps, rubella), rotavirus, and chickenpox.

2. Inactivated vaccines contain a killed version of the germ that causes an infection. You will usually require several doses over time to maintain immunity because these vaccines do not provide immunity as strong as a live vaccine. Examples include hepatitis A, influenza, and polio.

3. Subunit, recombinant, polysaccharide, and conjugate vaccines contain specific pieces of the germ such as a protein, sugar, or capsid (a casing around the germ). You may need booster doses to maintain strong immunity. Examples include hepatitis B, pneumococcal, meningococcal, and shingles.

4. Toxoid vaccines contain an inactivated version of a toxin (poison) made by a germ that causes disease. Examples include diphtheria and tetanus.

Why Do I Need Vaccines?

Vaccines have prevented suffering from common infections, helped many people live longer, and saved millions of lives. A deadly infection like smallpox was fully eradicated from the world because of vaccination. When more people get vaccinated, the more likely we are to eradicate a disease. When you get vaccinated, you protect yourself from deadly infections and prevent the spread of germs to vulnerable people like elderly persons or people with a weakened immune system.

Are Vaccines Effective?

When vaccines are administered at the right time in the right number of doses, they are extremely effective at preventing infections. However, no vaccine is 100 % effective. Some vaccines are more effective than others. For example, the MMR vaccine is 99 % effective after 2 doses, while the influenza vaccine is only 10 to 60 % effective depending on the year. Many vaccines are given early in childhood because children are the most vulnerable to serious infections. Follow your local health authority recommendations for proper timing of vaccinations to maximize their benefits. A modified schedule may be used only after consulting your healthcare provider.

Can Everyone Receive a Vaccine?

The majority of the population can safely receive all types of vaccines. A small proportion of people cannot get vaccinated because they have a weakened immune system. Therefore, they rely on those who are vaccinated to prevent the spread of harmful germs, a concept known as herd immunity.

What Is Herd Immunity?

For infections that are spread from person to person, it is important to ensure the maximum number of people are protected against the disease. This prevents the germ from getting into the population and spreading to vulnerable people. For example, to prevent the spread of measles, at least 95 % of the population need to have protective immunity.

Can I Receive More Than One Vaccine at a Time?

Yes, vaccines are often given together to protect against several infections at the same time.

What Are the Side Effects of Vaccines?

Vaccines are generally very safe, but like all medicines, they do have some side effects. Common side effects include:

  1. Injection site reactions (pain, swelling, redness).
  2. Fever.
  3. Shivering.
  4. Tiredness.
  5. Headache.
  6. Muscle and joint pain.

These are generally self-limiting and can be treated with over the counter pain medicines.

A rare side effect is anaphylaxis (severe allergic reaction) which occurs 1 in a million cases. For unique side effects pertaining to a specific vaccine, please consult your healthcare provider. The benefits of vaccinations generally far outweigh the risks.

Is It Better to Get the Infection or the Vaccine?

The diseases that vaccines prevent can be serious and sometimes fatal. Getting the infection, leads to suffering, missed days from school or work, lost productivity, the risk of infecting those around you, and sometimes serious complications. It is much better to get the vaccine than to get the infection.

Do Vaccines Cause Autism?

No, vaccines DO NOT cause autism. Very extensive research has shown that vaccines are not linked to autism.


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Last reviewed at:
10 Oct 2019  -  3 min read


Dr. Davie Wong

Dr. Davie Wong

Bachelor of Science, Pharmacy, Doctor of Medicine, Internal Medicine Residency, Infectious Disease Fellowship

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