Vaccines are a vital component of the medicine and drug industry that can keep diseases and illnesses at bay. There are different types of vaccines classified on the basis of how they are made. These include:
- Live or attenuated vaccines
- Dead or inactivated vaccines
- Conjugate vaccines
- Recombinant vaccines
- Toxoid vaccines
- DNA vaccines
The two main classifications of vaccines are: live and dead vaccines.
Live attenuated vaccines
These vaccines are termed as live because they are derived from disease-causing “wild” bacteria or viruses. These bacteria and viruses are weakened or “attenuated” by culturing them in a laboratory. After being injected, live attenuated vaccines grow and replicate inside the vaccinated person’s body to produce an immune response. This works so that the vaccine organism grows until the human body recognizes it as a foreign pathogen and produces antibodies against it. Thus when the body is exposed to actual disease pathogens, it is armored with antibodies to fight the disease. The immune response to an attenuated live vaccine is strong, and a single dose is sufficient for life. However, since the pathogen is live, it could mutate inside the body and no longer elicit the required immune response. There even exists a remote possibility of the microbe in the vaccine reverting back to its virulent form and causing disease.
Dead or inactivated vaccines
These vaccines consist of killed or inactivated forms of the pathogen, killed with either heat, chemicals like formalin, or radiation. These vaccines function when the immune system responds to the introduction of the virus, bacteria, or toxin produced by the germ. However, the immune response for these vaccines is not as strong as attenuated vaccines and thus repeated booster doses are required after a certain period of time for longer lasting immunity against diseases.
Differences between dead and live vaccines
Live attenuated vaccines consist of weakened viruses or bacteria and are therefore highly unstable. They require mandatory refrigeration so that the microbes remain weakened and the chances of mutation are lower. Dead inactivated vaccines, on the other hand, are quite stable and do not pose the risk of dead microbes mutating. Therefore they can be stored without refrigeration.
Another difference is that live vaccines elicit a strong immune response, similar to fighting the actual disease, and therefore a single dose is sufficient to last a lifetime. On the other hand, dead vaccines produce a comparatively weak response and therefore repeated booster doses are required periodically to refresh the immune system’s memory.
Since live vaccines are unstable, they cannot be given to individuals with suppressed, damaged, or weakened immune systems, such as AIDS patients or those undergoing chemotherapy, as the reaction to the live microbe could cause the actual disease itself. Dead vaccines, on the other hand, are completely safe and can be administered to those with weak or damaged immune systems as well.
Examples of live and dead vaccines
Live viral vaccines are available for diseases such as mumps, rubella, measles, yellow fever, varicella, and influenza (administered intranasally); the oral polio vaccine also falls in this category. Attenuated live bacterial vaccines include the oral typhoid vaccine and BCG.
Dead inactivated whole viral vaccines are available for diseases such as rabies, polio, influenza, and hepatitis A. Dead inactivated whole bacterial vaccines provide protection against cholera, typhoid, pertussis, and plague. Fractional vaccines that contain subunits provide protection against influenza, acellular pertussis, and hepatitis B. Toxoid dead vaccines are available for tetanus and diphtheria.