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A Patient's Guide to Vaccines

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A Patient's Guide to Vaccines

4 min read


Vaccines strengthen the immune system against certain microorganisms that can cause serious infections and even death. Read the article below to learn more.

Written by

Dr. Davie Wong

Medically reviewed by

Dr. Sneha Kannan

Published At April 12, 2019
Reviewed AtAugust 28, 2023

What Is Immune System?

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

What Is a Vaccine?

A vaccine is a medicine that boosts a person’s immunity against harmful microorganisms and greatly reduces the risk of contracting a serious infection. Vaccines 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 a person is ever exposed to that germ again, the immune system will be able to fight it off, restricting its effects or completely eliminating them. Vaccines are also referred to as vaccinations, immunizations, shots, or needles. Vaccines are very important as they aid in preventing the spread of contagious, critical, and fatal diseases. These include certain diseases like measles, polio, mumps, chicken pox, whooping cough, diphtheria, HPV (human papilloma virus), and COVID-19.

How Is a Vaccine Administered?

Vaccination plays an important role in building the immune system of an individual. For children aged three and older, most vaccines are injected into the deltoid muscle in the shoulder (intramuscular). For children under the age of three, vaccines are commonly injected into the thigh muscle. Some vaccines are injected right beneath the skin (subcutaneous) or administered by mouth (oral). The live attenuated influenza vaccine (intranasal) is the only vaccine given through the nose.

What Are the Types of Vaccines?

There are four types of vaccines.

1. Live-attenuated vaccines, which 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 that contain a killed version of the germ that causes an infection. A person 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 vaccines.

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). An individual may need booster doses to maintain strong immunity. Examples include hepatitis B, pneumococcal, meningococcal, and shingles vaccines.

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

Why Do Individuals 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, it is more likely to eradicate a disease. When an individual gets vaccinated, they protect themself from deadly infections and prevent the spread of microorganisms 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 in preventing infections. However, no vaccine is 100 percent effective. Some vaccines are more effective than others. For example, the MMR vaccine is 99 percent effective after two doses, while the influenza vaccine is only 10 percent to 60 percent effective, depending on the time when it was taken. Many vaccines are given early in childhood because children are the most vulnerable to serious infections. Follow the local health authority's recommendations for the proper timing of vaccinations to maximize their benefits. A modified schedule may be used only after consulting the 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 microorganisms, 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 needs to have protective immunity.

Can an individual 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:

  • Injection site reactions (pain, swelling, redness).

  • Fever.

  • Shivering.

  • Tiredness.

  • Headache.

  • 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 in one in a million cases. For unique side effects pertaining to a specific vaccine, please consult the 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 people around, 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.


There are so many confusions and misconceptions about vaccines. As everybody needs vaccines for the betterment and wellness of the individual and society, it is recommended to get a vaccination, which is a safe and effective way to prevent the spread of contagious and deadly diseases.

Vaccines may have some side effects, but their administration brings so many benefits that can outweigh any risks or side effects.

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Dr. Davie Wong
Dr. Davie Wong

HIV/AIDS specialist


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