Tell Me More: Vaccines

What is a vaccine?

Immunization is widely recognized as one of the most effective interventions for reducing the impact of many infectious diseases, and according to the World Health Organization, immunization is “a global health and development success story, saving millions of lives every year”. Immunization is achieved through the use of vaccines, a type of drug that essentially trains the body’s immune system to increase its ability to fight infection. When vaccines are readily available, they are able to significantly decrease the incidence, and in some cases eliminate certain infectious diseases including polio, tetanus, rubella, measles, mumps, and pertussis (whooping cough). Vaccines are designed to prevent or decrease the severity of diseases that can cause serious illness, long-term disability, and death. 

How do vaccines work?

Vaccines contain weakened or inactivated versions of a pathogen (a disease-causing organism such as a virus or a bacteria), or parts of a pathogen (antigens). The vaccine itself does not cause disease in the person receiving it, but works by triggering an immune response as if the person were exposed to the live pathogen. The body first recognizes the weakened pathogen or antigen in the vaccine as foreign (not belonging to the body). The immune system then makes special proteins (antibodies) that help destroy the pathogen the vaccine was created to protect against.

If the person is later exposed to the same pathogen, their immune system remembers it, and quickly produces antibodies to target the pathogen and remove it from the body before it has a chance to cause infection or serious illness.

Types of vaccines

There are different types of vaccines available, but they all work to stimulate a response from your immune system to help protect you against disease. 

Live-attenuated vaccines
Live vaccines use a weakened (attenuated) form of the disease-causing pathogen. Although the pathogen is a live specimen and can replicate in the body, in its weakened form, it does not cause disease. Because live-attenuated vaccines are so similar to the natural infection that they help prevent, they create a strong and long-lasting immune response. Just 1 or 2 doses of most live vaccines can give you a lifetime of protection against a pathogen and the disease it causes.

Live vaccines are currently used to protect against:

• Chickenpox (varicella)
• Measles, mumps, rubella (MMR)
• Rotavirus
• Smallpox
• Yellow fever

Inactivated vaccines
This type of vaccine uses an inactivated version of the disease-causing pathogen. Inactivating a pathogen destroys its ability to replicate, but keeps it “intact” so that the immune system can still recognize it. Inactivated vaccines usually provide shorter protection than live-attenuated vaccines, and booster doses are more likely to be required to create long-term immunity.

Inactivated vaccines are currently used to protect against:

• Hepatitis A
• Influenza
• Polio
• Rabies

Subunit vaccines
These vaccines include only the components of pathogens or antigens which best produce a strong and effective immune response, instead of the whole pathogen. They cannot cause disease and can be used by almost everyone who needs them, including people with weakened immune systems. Important subunit vaccines include polysaccharide, conjugate, and protein-based vaccines. These vaccines may require booster doses to maintain ongoing protection.

These types of vaccines are currently used to protect against:

• Hepatitis B
• HPV (Human papillomavirus)
• Influenza
• Meningococcal disease
• Pertussis (whooping cough)
• Pneumococcal disease
• Shingles

Toxoid vaccines
Toxoid vaccines prevent diseases caused by bacteria that produce toxins (poisons) in the body. The vaccines are produced using weakened toxins (toxoids) so they cannot cause disease. When a person receives a vaccine containing a toxoid, their immune system responds and learns to fight off toxin produced by bacteria. These vaccines may require booster doses to maintain ongoing protection.

Toxoid vaccines are currently used to protect against:

• Diphtheria
• Tetanus

mRNA vaccines
These vaccines use messenger RNA (mRNA) to teach the body’s cells how to make a protein (antigen) that is found on the pathogen the vaccine protects against. This triggers an immune response to produce antibodies and activate other immune cells which will protect against future infections with the pathogen. mRNA vaccines do not contain live pathogens, cannot reproduce in the body, and do not cause disease. A benefit of mRNA vaccines is that unlike typical vaccines which can take months or years to create, they can be developed and manufactured quickly. These vaccines may require booster doses to maintain ongoing protection.

mRNA vaccines are currently used to protect against:

• COVID-19

Viral vector vaccines
This type of vaccine uses a viral vector - a harmless, unrelated virus - to deliver genetic instructions (DNA) to the body’s cells to produce a viral protein (antigen) found on the pathogen the vaccine protects against. This triggers a response from the immune system to produce antibodies and activates other immune cells, which teaches the body’s cells to protect against future infections with the pathogen. Viral vector vaccines do not contain live pathogens, cannot reproduce in the body, and do not cause disease. These vaccines may require booster doses to maintain ongoing protection.

Viral vector vaccines are currently used to protect against:

• COVID-19
• Smallpox

Vaccines are the most effective way to prevent many infectious diseases. The more vaccinated individuals in a community, the more difficult it becomes for a disease to spread.