A vaccine is a biological preparation that provides active acquired immunity for a disease.

• Typically contains an agent that resembles a disease-causing micro-organism.
• Often made from weakening or killed form of microbes or surface protein of microbe.
• The biological agent stimulates the immune system of our body, it recognizes the agent as a threat.
• Our immune system recognizes the foreign particle and kills it. (the mechanism for killing that type of microorganism is stored in the memory of our cells for the next time when again that microorganism tries to enter inside our body our immune system knows the process of killing that type of microorganism stored as memory.)
• The administration of vaccines is called Vaccination.
• Vaccine and vaccination come from the Variolae vaccine.
• The vaccination term was given by Edward Jenner.
• Father of vaccination: Edward Jenner (cowpox, 1798)
• The second generation of the vaccine was introduced by Louis Pasteur (1881, chicken cholera and anthrax vaccines)

Types of vaccine

• Attenuated vaccines
• Inactivated vaccines
• Subunit vaccines
• Toxoid vaccines
• Conjugate vaccines
• DNA vaccines
• Recombinant vaccines

Attenuated vaccines (live)

• Contains living microorganism.
• The microorganism is weakened so it isn’t lethal.
• Used to produce a broad immune response.
• Because the attenuated type of vaccine contains live pathogens, so these vaccines are not given to those patients who have weak immunity.

E.g.  for measles, mumps, Rotavirus.

Inactivated vaccines

• Contain an inactivated microbe.
• Safer than live vaccines.
• Inactivated vaccines contain the dead pathogen, so it may not be accurate.
• Microbes inactivated using chemical, heat, radiation

E.g. for Rabies, hepatitis, influenza, Polio.

Subunit Vaccines

• Use of proteins subunits of microbe.
• Include antigens/epitopes.

E.g. for Plague, HPV (human papillomavirus).

Toxoid vaccine

• Use of a toxin from a microbe.
• The use of toxic(weaken) compounds may cause illness.

E.g.  for Tetanus, Diphtheria.

Conjugate vaccines

• Some bacteria have an outer coating of polysaccharide.
• The capsid of polysaccharide contains bacterium antigens.
• These polysaccharides used to make vaccines.

E.g. for Hemophilus, Influenzae type B.

DNA vaccines

• still in development mode (DNA vaccines).
• Contain both (organism and its part).
• Using genetic material of bacterium for vaccine preparation.

E.g. for Influenza

Recombinant vaccines

• In the development phase.
• Produced by RDT (recombinant DNA technology).
• Insertion of DNA encoding antigen using vectors, it stimulated immune response.

E.g. hepatitis B, HIV, rabies

How a vaccine prevents us from disease?

A vaccine works by creating a memory for fighting against disease. During this process when we inject microbes/vaccine certain molecules are produced from the pathogen, known as an antigen. Our body makes antibodies against these antigens and keeps a memory against that microorganism. The next time when the pathogen tries to enter our body, our immune system recognizes the antigen and starts attacking the foreign particle (pathogens). Our immune system aggressively starts attacking these antigens before the pathogen causes more damage to our body.

Advantages and disadvantages of vaccination

Advantages	Disadvantages
Protects from various diseases	Not 100% accurate to work
Prevent the disease from spreading	May cause side effects
Using subunit/conjugate vaccine the risk of adverse reaction is low	Only a few of vaccines can be produced as subunit/conjugate.