What Is a Vaccine?

You know what a vaccine is, right?

The flu shot you get each year is a vaccine.

Vaccine: A product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease. Vaccines are usually administered through needle injections, but can also be administered by mouth or sprayed into the nose.

Immunization: The Basics

The smallpox shot that Edward Jenner developed was a vaccine.

Vaccine Definitions

While that is an easy enough definition to understand, that there are many different types of vaccines does make it a little more complicated.

There are:

• Live-attenuated vaccines – made from a weakened or attenuated form of a virus or bacteria
• Inactivated vaccines – made from a killed form of virus or bacteria
• Subunit, recombinant, polysaccharide, and conjugate vaccines – made from only specific pieces of a virus or bacteria
• Toxoid vaccines – made to target a toxin that a bacteria makes and not the bacteria itself

And of course all of these types of vaccines work to produce immunity to specific diseases – vaccination.

Immunization: A process by which a person becomes protected against a disease through vaccination. This term is often used interchangeably with vaccination or inoculation.

Immunization: The Basics

What other definitions are important to know when you talk about vaccines?

• active immunity – immunity that you get from having a disease (natural immunity) or getting a vaccine and making antibodies
• adjuvant – a substance that helps boost your body’s immune response to a vaccine so that you can use a minimum amount of antigen, reducing side effects
• antibodies – protective proteins that you make against antigens
• antigens – specific substances (can be part of a virus or bacteria) that trigger an immune response
• attenuation – a virus or bacteria that is made less potent, so that it can produce an immune response without causing disease
• elimination – getting rid of a disease in a specific area
• endemic – the baseline level of disease in an area
• eradication – getting rid of a disease everywhere (smallpox)
• epidemic – an increase in the number of cases of a disease over a large geographic area
• herd immunity – when enough people in a community are protected and have immunity, so that disease is unlikely to spread
• immunity – protection against a disease
• incubation period – how long it takes to develop symptoms after you are exposed to a disease
• outbreak – an increase in the number of cases of a disease over a small geographic area
• pandemic – an increase in the number of cases of a disease over several countries or continents
• passive immunity – temporary immunity that you get after being given antibodies, either via a shot of immunoglobulin or a mother’s antibodies are transferred to her baby through her placenta
• placebo – classically defined as “a comparator in a vaccine trial that does not include the antigen under study”
• quarantine – isolating someone so that they don’t get others sick
• titer – an antibody count that can often be used to predict immunity

Got all of that?

So what about variolation, the process that was used before Jenner developed his smallpox vaccine? Was that also a vaccine?

It did produce immunity to smallpox, which is the basic definition of a vaccine, but still, variolation is typically concerned an immunization technique and not a vaccine.

More on Vaccine Definitions

• CDC – Immunization: The Basics
• CDC – Vaccine and Immunization Glossary
• WHO – Vaccine Safety Glossary
• Vaccines411 Glossary
• CDC – Epidemic Disease Occurrence
• CDC – The Principles of Disease Elimination and Eradication
• History of Vaccines Glossary of Terms
• What are vaccines?
• Vaccine Types
• What is herd immunity?
• WHO – Immunization
• WHO – Guidelines on clinical evaluation of vaccines: regulatory expectations
• The Origin of the Word ‘Vaccine’