Vaccines work by exposing the body to antigens from pathogens to trigger an immune response. When first exposed, it takes time for the body to produce antibodies, but memory cells remain to allow faster response to future exposure. Vaccines introduce antigens to stimulate this immune response, protecting against disease. Major types include inactivated, live-attenuated, mRNA, and subunit/toxoid vaccines. Vaccination has helped reduce disease and mortality worldwide through innovations since Jenner's smallpox vaccine and ongoing efforts like polio and COVID-19 vaccine development.

1. Vaccines
• Germs are all around us, both in our environment and in our bodies. When a person is susceptible
and they encounter a harmful organism, it can lead to disease and death.
• The body has many ways of defending itself against pathogens (disease-causing organisms). Skin,
mucus, and cilia (microscopic hairs that move debris away from the lungs) all work as physical
barriers to prevent pathogens from entering the body in the first place.
• When a pathogen does infect the body, our body’s defenses, called the immune system, are
triggered and the pathogen is attacked and destroyed or overcome.

2. The body's natural response
• A pathogen is a bacterium, virus, parasite or fungus that can cause disease within the body.
• The subpart of a pathogen that causes the formation of antibodies is called an antigen.
• The antibodies produced in response to the pathogen’s antigen are an important part of the immune
system.
• Each antibody, or soldier, in our system is trained to recognize one specific antigen.
• When the human body is exposed to an antigen for the first time, it takes time for the immune
system to respond and produce antibodies specific to that antigen. In the meantime, the person is
susceptible to becoming ill.
• Once the antigen-specific antibodies are produced, they work with the rest of the immune system
to destroy the pathogen and stop the disease.
• Once the body produces antibodies in its primary response to an antigen, it also creates antibody-
producing memory cells, which remain alive even after the pathogen is defeated by the antibodies.
• This means that if the person is exposed to a dangerous pathogen in the future, their immune
system will be able to respond immediately, protecting against disease.

3. A vaccine is a preparation that is administered (as by injection) to stimulate the body’s immune
response against a specific infectious agent or disease: such as
• An antigenic preparation of a typically inactivated or attenuated pathogenic agent (such as a bacterium
or virus) or one of its components or products (such as a protein or toxin) a trivalent influenza vaccine,
oral polio vaccine
• A preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the
cells of the body to produce an antigenic substance (such as a fragment of virus spike protein)
 Some vaccines require multiple doses, given weeks or months apart. This is sometimes needed to
allow for the production of long-lived antibodies and the development of memory cells.
 Vaccinating not only protects yourself but also protects those in the community who are unable to be
vaccinated. If you are able to, get vaccinated.

5. History of Vaccines
• Edward Jenner is considered the founder of vaccinology in the West in 1796.
• Edward Jenner observed that milkmaids and others previously infected with cowpox were immune to
smallpox. Cowpox caused lesions similar to smallpox, but the lesions were localized, and the disease was
much milder and not considered deadly. Edward Jenner expands on this discovery and inoculates 8-year-old
James Phipps with matter collected from a cowpox sore on the hand of a milkmaid. Despite suffering a local
reaction and feeling unwell for several days, Phipps made a full recovery.
• Two months later, Jenner inoculates Phipps with matter from a human smallpox sore in order to test Phipps’
resistance. Phipps remains in perfect health, and becomes the first human to be vaccinated against smallpox.
The term ‘vaccine’ is later coined, taken from the Latin word for cow, vacca.
• For almost eighty years, cowpox vaccination against smallpox remained the only vaccine in use around the
world.
• Louis Pastuer a French biochemist In 1872, developed the first laboratory-produced vaccine: the vaccine for
fowl cholera in chickens.
• 1885, Louis Pasteur successfully prevents rabies through post-exposure vaccination.

6. • From 1918 to 1919, the Spanish Flu pandemic kills an estimated 20–50 million people worldwide,
including 1 in 67 United States soldiers, making an influenza vaccine a US military priority.
• In 1939, bacteriologists Pearl Kendrick and Grace Eldering demonstrated the efficacy of
pertussis (whooping cough) vaccine.
• In 1945, the first influenza vaccine was approved for military use, followed in 1946 by approval for
civilian use.
• From 1952–1955, the first effective polio vaccine was developed by Jonas Salk and trials began.
• By 1960, the second type of polio vaccine, developed by Albert Sabin, was approved for use. Sabin’s
vaccine was live-attenuated (using the virus in weakened form) and could be given orally, as drops, or on
a sugar cube.
• In 1967, the World Health Organization announced the Intensified Smallpox Eradication Programme,
which aims to eradicate smallpox in more than 30 countries through surveillance and vaccination.
• A plasma-derived inactivated vaccine against the hepatitis B virus was approved for commercial use from
1981 to 1990, and a genetically engineered (or DNA recombinant) vaccine, developed in 1986, is still in
use today.
• In 1971 the measles vaccine (1963) is combined with recently developed vaccines against mumps (1967)
and rubella (1969) into a single vaccination (MMR) by Dr. Maurice Hilleman.

7. • In 1974 the Expanded Programme on Immunization (EPI, now the Essential Programme on
Immunization) was established by WHO to develop immunization programs throughout the world.
• In 1988 following the eradication of smallpox, WHO set its sights on poliomyelitis, launching
a Global Polio Eradication Initiative.
• In 2016 the success of the Meningitis Vaccine Project highlighted the key role public-private
partnerships can play in helping to develop vaccines.
• In 2019, WHO prequalifies an Ebola vaccine for use in countries at high risk.
• In 2021, effective COVID-19 vaccines are developed, produced, and distributed with unprecedented
speed, some using new mRNA technology.
 From groundbreaking practices in the 1500s to the new technologies used in the COVID-19 vaccine,
we have come a long way. Vaccines now help protect against more than 20 diseases, from pneumonia
to cervical cancer and Ebola; and in just the last 30 years, child deaths have declined by over 50%,
thanks in large part to vaccines. But more must be done.

8. Types of vaccines
There are several types of vaccines, including:
• Inactivated vaccines
• Live-attenuated vaccines
• Messenger RNA (mRNA) vaccines
• Subunit, recombinant, polysaccharide, and conjugate vaccines
• Toxoid vaccines
• Viral vector vaccines
Inactivated vaccines
• Inactivated vaccines use the killed version of the germ that causes a disease.
• Inactivated vaccines usually don’t provide immunity (protection) that’s as strong as live vaccines. So you may
need several doses over time (booster shots) in order to get ongoing immunity against diseases.
• Inactivated vaccines are used to protect against hepatitis A, flu, polio, rabies.

9. Live-attenuated vaccines
• Live vaccines use a weakened (or attenuated) form of the germ that causes a disease.
• These vaccines are so similar to the natural infection that they help prevent, they create a strong and long-
lasting immune response. But live vaccines also have some limitations. For example: As they contain a
small amount of the weakened live virus, some people should talk to their healthcare provider before
receiving them, such as people with weakened immune systems, long-term health problems, or people
who’ve had an organ transplant.
• Rotavirus, smallpox, chickenpox, yellow fever, measles, mumps, rubella
Messenger RNA vaccines—also called mRNA vaccines
• mRNA vaccines make proteins in order to trigger an immune response. mRNA vaccines have several
benefits compared to other types of vaccines, including shorter manufacturing times and, because they do
not contain a live virus, no risk of causing disease in the person getting vaccinated.
• COVID-19

10. Subunit, recombinant, polysaccharide, and conjugate vaccines
• Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germ—like its
protein, sugar, or capsid (a casing around the germ).
• These vaccines give a very strong immune response that’s targeted to key parts of the germ. They can
also be used on almost everyone who needs them, including people with weakened immune systems
and long-term health problems.
• One limitation of these vaccines is that you may need booster shots to get ongoing protection against
diseases.
• Hib (Haemophilus influenza type b) disease, hepatitis B, HPV (Human papillomavirus), Whooping
cough, Pneumococcal disease, Meningococcal disease, Shingles
• Toxoid vaccines
• Toxoid vaccines use a toxin (harmful product) made by the germ that causes a disease. They create
immunity to the parts of the germ that cause disease instead of the germ itself. That means the immune
response is targeted to the toxin instead of the whole germ.
• Like some other types of vaccines, you may need booster shots to get ongoing protection against
diseases.
• Diphtheria, Tetanus

11. Viral vector vaccines
• Viral vector vaccines use a modified version of a different virus as a vector to deliver protection. Several
different viruses have been used as vectors, including influenza, vesicular stomatitis virus (VSV),
measles virus, and adenovirus, which causes the common cold. Adenovirus is one of the viral vectors
used in some COVID-19 vaccines being studied in clinical trials.
• Viral vector vaccines are used to protect against: COVID-19