Edward Jenner invented the first vaccine in 1798. It was called Smallpox vaccine as it gave the protection against Smallpox virus. Interestingly, the vaccine was composed of an attenuated form of Cowpox virus, which is a similar virus to Smallpox virus. Since then, the scientists have come a long way in inventing various types of vaccines against many deadly diseases.
Live, Attenuated vaccines
These types of vaccines are weakened or altered viruses rendered incapable to cause a disease due to their limited or no replication ability inside the host. Live vaccines mimic the natural infection best, so are very effective and also provide longer lasting immunity. In rare cases, the virus may mutate and revert back to its virulent form, and cause the disease in people with weak immunity e.g., Oral Polio Vaccine.
Killed or Inactivated Vaccines
These types of vaccines contain Inactivated viruses or killed bacteria, created by exposing to heat or harsh chemicals such as formaldehyde or formalin. Inactivated or killed pathogens can’t replicate inside the host, but are very much in a form that can be recognized by our immune system. They are considered safer than live vaccines, as they can’t replicate at all and, show no reversion to cause a disease even in rare cases. However, they provide immunity for shorter duration and require booster shots.
Diphtheria, Tetanus (part of DTP combined immunization)
These types of vaccines are specially generated for some diseases, where the illness is not caused by the pathogen itself but by effect of toxins produced by it. Toxoids are inactivated form of toxins generated using heat and chemical exposure techniques, e.g., Tetanus toxoid (inactivated neurotoxin, Tetanospasmin). Toxoids when injected inside the body are recognized by the immune system as toxins and immunity is achieved against future infections by the toxin generating pathogens.
These types of vaccines contain only bits and pieces of the pathogens (antigens) for which they train the immune system to protect.
Subunit vaccines are made by extracting the specific protein from a pathogen, capable to provoke an immune response, e.g., acellular Pertussis vaccine and influenza vaccine. These vaccines are very safe and do not produce any adverse reactions as they contain only parts of the pathogen rather than the whole pathogen.
Recombinant subunit vaccines can also be made by inserting the gene coding for the antigenic protein in the non pathogenic microbes, and then growing them in cultures, and extracting the proteins to make the vaccine e.g., Hepatitis B Vaccine
These types of vaccines are made by chemically linking a carrier protein to the antigenic pieces from surface coatings of target pathogenic bacteria. The antigenic pieces alone are not able to induce a strong immune response, but when combined with the protein are able to provide long lasting immunity e.g., Typhoid Conjugate Vaccine and Pneumococcal Conjugate Vaccines.
Vaccine is by far the most important invention till date, for the welfare of entire humankind. Learn more about how Vaccines work to provide us immunity.