Vaccine Epidemiology


Many physicians may toss around phrases such as “the efficacy of the drug is fantastic” or “the drug effectiveness is amazing” and many parents and people are satisfied and put at comfort with these phrases as if they are interchangeable. It is your right to know the difference between efficacy and effectiveness so that you can make an informed decision when thinking about the vaccine option for you or your child. Both efficacy and effectiveness are important when talking about vaccines. When a new vaccine is licensed by the Food and Drug Administration and other global regulatory authorities the vaccine typically goes through a double-blind, randomized, controlled trial. Vaccine efficacy trials represent tests done in the most ideal circumstances or the best case scenario of vaccine safety. The benefits of testing the efficacy of a drug are crucial for eliminating bias through randomized double-blind trials. Often efficacy is confused with effectiveness. Effectiveness if the test of the drug in the real world on the population. Vaccine effectiveness is proportional to vaccine efficacy but is also affected by how well target groups in the population are immunized. The rate and potency of how well target groups are immunized in the population may alter with different conditions and factors such as access to health care and vaccine cost. Effectiveness is a more versatile measurement of the drug’s potential to work properly when the environment and population for both study and intended use are equivalent.

  1. [i] Clemens J, Brenner R, Rao M, Tafari N, Lowe C

. Evaluating new vaccines for developing countries. Efficacy or effectiveness? JAMA 1996;275:390-397.


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