What are vaccines?

Picture a battle field. The enemy is charging down, weapons in-hand, ready to attack. On the other end, multiple lines of defense are in position to tackle the enemy. Our body is like this battlefield and germs and diseases are the enemy.

Skin and the mucous membranes form  the first line of defence and help keep the germs away. 1If the germs manage to break through this physical barrier and enter the body, the second line gets into action. Cell-level and chemical defences are activated.1  Cell level defence is when the body releases substances to ensure that the damage to the body is minimal. The acid in our stomach which kills harmful germs is an example of chemical defense. 2

In the case that germs manage to overpower both these obstacles, the body deploys its master weapon – the immune system, to annihilate the ememy. 3The immune system not only destroys the germs but also records them as the “enemy” and stores them in its memory.4 Thus, if they attack again, the body is prepared to execute its plan of action without any delays. For example, a child is infected with the measles virus in his childhood and his immune system helps him to recover. If the same child is attacked again by the measles virus, his immune system will recall how to deal with it, rapidly get into action and destroy that virus before it takes over the body.

Vaccines work in the same manner as the immune system, except they are preventive and thus protect our body from the very first attack of some serious infections.  They feed off our body’s built-in system that is designed to protect us against any foreign objects, like bacteria and viruses, which do not belong inside us.


For how long do vaccines provide protection ?

The duration of protection differs for various diseases and for various vaccines. Usually, a single dose of vaccine is enough to provide protection against a disease. However, sometimes more than one dose would be needed for preventing certain diseases. Some antibodies provide protection for lifetime, whereas, some may need booster doses. Hence some vaccines have booster doses to be taken in a stipulated period, after the first dose.

For example, measles antibody last for a lifetime, while, antibody to tetanus can fall below the level of protection, and so, booster doses are needed for tetanus.

Viruses such as influenza can change enough to make the antibodies ineffective. That’s the reason, influenza vaccines are to be given every year.

Additionally, here are more differences:

  • Live vaccines provide more protection as compared to the killed variety of vaccines.
  • Killed vaccines usually need more than one dose so that the body becomes able to fight serious diseases.
  • Also, if there is a lot of gap between the first and the second dose of vaccine, it may affect the individual’s immunity for that particular disease and may not offer the desired protection. Hence, doctors always advise to follow regular schedules for vaccination.



Read more on vaccines
Know more about the Benefits of vaccines


  1. Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The front line of host defense.
  2. Antimicrob Agents Chemother. 2006 Nov; 50(11): 3901–3904.
  3. J Allergy Clin Immunol. 2010 Feb; 125(2 Suppl 2): S3–23.
  4. Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. The innate and adaptive immune systems. 2010 Dec 7
  5. Yale J Biol Med. 2014 Dec; 87(4): 417–422.