AlegsaOnline.com

Vaccine: purpose, types, history, and public-health role

A vaccine is a biological preparation that trains the immune system to resist a specific infectious agent. This article explains how vaccines work, their varieties, history, uses, and important distinctions.

Author: Leandro Alegsa Creation date: November 13, 2022 Last updated: May 24, 2026

simple.wikipedia.org · Public domain

A vaccine is a biological preparation given to stimulate immune protection against a particular infectious agent. Vaccines are designed to target a specific microorganism, and their administration is commonly called vaccination. Many vaccines are delivered by injection, although other routes—oral or nasal—are used for some formulations. When effective, a vaccine reduces the chance of symptomatic disease, severe illness, and onward transmission.

How vaccines work

Vaccination trains the immune system to recognize features of a pathogen without causing the full illness. The exposure prompts the body to produce immune memory—specialized cells and antibodies—so that if the real pathogen is encountered later, the immune response is faster and more effective. Vaccines can protect against infections caused by bacteria and viruses, and in some cases they reduce carriage and spread as well as disease.

Main types of vaccines

Live attenuated: contain weakened forms of a live agent that replicate poorly in humans; historically these derive from organisms that were once alive.
Inactivated or killed: contain pathogens that have been killed so they cannot reproduce but still stimulate immunity.
Subunit, conjugate, and protein-based: include only parts of the pathogen (proteins or sugars) to focus the immune response.
Toxoid: use inactivated bacterial toxins to prevent disease caused by toxin-producing bacteria.
New platform vaccines: such as nucleic-acid (mRNA) or viral-vector vaccines, which use genetic instructions or harmless carriers to prompt cells to produce a target antigen.

Different vaccines require different schedules and sometimes booster doses to maintain protection. Some are formulated with adjuvants—substances that enhance the immune response—so smaller amounts of antigen can be effective.

History and origins

The term "vaccine" is derived from the Latin vacca, meaning "cow", a reference to the first widely recognized use of cowpox material to prevent smallpox. In 1796, Edward Jenner observed that milkmaids who had contracted cowpox were largely protected against smallpox and used material from cowpox lesions to confer immunity. Long before Jenner, practitioners in some cultures used a form of variolation—introducing material from smallpox lesions into healthy people, sometimes by blowing powdered material into the nostrils—to induce a milder infection that provided protection.

Uses, impact, and distinctions

Vaccines are a cornerstone of public health: by preventing disease in individuals and reducing transmission at the population level, they lower illness, disability, and death. The concept of herd immunity describes how high vaccine coverage can protect people who are not immune. A vaccine is a preparation intended to induce immunity; the resulting state is often called immunization. Vaccines are specific to their target pathogens, though some may offer partial cross-protection against related strains. Safety monitoring and clinical trials are standard parts of vaccine development to evaluate effectiveness and rare adverse events.

Practical considerations

Selection of a vaccine type depends on the pathogen, the population to be protected, and practical factors like storage and delivery. For example, seasonal influenza vaccines are updated regularly to match circulating strains. Advances in biotechnology have expanded the range of vaccine strategies and sped up development for emerging threats, while established vaccine programs continue to control or eliminate many infectious diseases.

Further reading and technical resources can be found through public health organizations and scientific literature; treatment and vaccination decisions should follow national guidance and healthcare professionals' advice.

In active immunization, the vaccine contains or produces an antigen against which the patient's immune system forms its own antibodies within 14 days, resulting in lasting immunity. If only antibodies are vaccinated, one speaks of passive immunization, the protection occurs immediately, but lasts only for a short time.

Usually vaccine is injected into a muscle by syringe

Attenuated live vaccine

→ Main article: Attenuation

Live vaccines contain attenuated bacteria or viruses that can usually still multiply and trigger an immune response, but usually not a disease. An attenuated virus that is still replicated by a cell is also called a "live vaccine". The term has become established, although strictly speaking it is not correct, because viruses are not living organisms.

A live attenuated vaccine is usually much more effective than an inactivated vaccine. In rare cases, after the application of such a vaccine, a mutation (reversion) towards the non-attenuated initial form can occur during the possible multiplication of the pathogens, through which the disease can occur after all.

Examples of attenuated vaccines include the oral polio vaccine (OPV) abandoned in Europe, which very rarely caused vaccine poliomyelitis, the MMR(V) vaccine, the smallpox vaccine of the time, the Bacillus Calmette-Guérin, and vaccines against yellow fever. Both live and inactivated vaccines are available for typhoid vaccination. Attenuation is usually achieved by serial infections of non-species cell cultures, embryonated chicken eggs or laboratory animals, in which the respective pathogen adapts to the new host species and often simultaneously loses adaptations to the species of the inoculated, resulting in a reduction in pathogenicity.

Some live vaccines are treated by additional methods. Cold-adapted strains can only replicate at temperatures around 25 °C, which limits the viruses to the upper respiratory tract. In the case of temperature-sensitive strains, replication is restricted to a temperature range of 38-39 °C and, again, infestation of the lower respiratory tract does not occur.

Dead Vaccine

→ Main article: Dead vaccine

Inactivated vaccines contain inactivated or killed viruses or bacteria or components of viruses, bacteria or toxins. These can no longer multiply in the body or poison it, as tetanospasmin could, but they also trigger a defence reaction (immune response). Examples are the toxoid vaccines and vaccines against influenza (influenza vaccine), cholera, bubonic plague, hepatitis A or hepatitis B (hepatitis B vaccine).

Dead vaccines are divided into:

Toxoids: Toxoids are detoxified toxins of pathogenic microorganisms. These vaccines are used in cases where it is not the pathogens themselves but primarily their toxins that cause the disease symptoms, as in the case of tetanus and diphtheria.
Inactivated whole-particle vaccines: Inactivation of viruses by fixation using a combined application of formaldehyde, beta-propiolactone and psoralen.
Cleavage vaccines: destruction of the virus surface with detergents or strong organic solvents.
Subunit vaccines: the surface is completely dissolved and specific components (haemagglutinin and neuraminidase proteins) are purified out. Another possibility is to produce the subunits recombinantly. Subunit vaccines are only slightly immunogenic, but have few side effects.

Inactivated vaccines require immunostimulatory adjuvants, most commonly alumiunium adjuvants.

Questions and Answers

Q: What is a vaccine?

A: A vaccine is an invented preparation that is given to prevent a specific infectious disease. It usually works against the microorganism for which it was prepared and is administered through an injection called vaccination.

Q: How does a vaccine work?

A: At its best, a vaccine gives immunity to an infectious disease caused by a particular microorganism (bacteria or virus). For example, the flu vaccine makes it very much less likely that a person will get the 'flu.

Q: What are vaccines made of?

A: Vaccines can be made from something that was alive or built up by viral biochemistry. Each vaccine has its own history and what is true of one might not be true of another.

Q: Where does the word "vaccine" come from?

A: The word "vaccine" comes from the Latin vacca, meaning "cow".

Q: Who first used cowpox to protect people against smallpox?

A: In 1796, Edward Jenner used a milkmaid infected with cowpox (variolae vaccinae) to protect people against smallpox.

Q: What is the use of vaccines called?

A: The use of vaccines is called vaccination.

Q: Was vaccination done before Jenner's discovery in 1796?

A: Yes, powdered smallpox material was blown up the nostrils of subjects prior to Jenner's discovery in 1796.

Author

AlegsaOnline.com - Vaccine - Leandro Alegsa

Creation date: November 13, 2022
Last updated: May 24, 2026

URL: https://en.alegsaonline.com/art/103836