Vaccine Effectiveness

Vaccines help the body remember a microorganism to be able to fight it off when the need comes. However, vaccines are not foolproof and do not guarantee complete protection from disease.

This could be due to various reasons. Sometimes this is because the host's immune system simply doesn't respond adequately or at all. This could be in diseased persons with lowered immunity e.g. in diabetics, those on steroids or other immunity suppressing drugs, or those with HIV infection.

Image Credit: Favebrush/Shutterstock

Image Credit: Favebrush/Shutterstock

The reason for non-development of immunity to a disease could also be because the host's immune system does not have a B cell capable of generating antibodies against the antigen or microbe or the immune system may not be strong enough to fight off the infection.

Efficacy of a vaccine

The efficacy of a vaccine is different from its effectiveness. It is dependent on several factors such as:

  • adherence to vaccine schedules
  • the disease – some diseases have vaccines against them that perform better than for other diseases
  • the strain of vaccine – some vaccine strains are more effective than others
  • non-responders – some individuals do not respond to certain vaccines at all. The cause may lie in the race, ethnicity or genetics of the individual

The mathematical deduction of protective vaccine efficacy is nearly 100 years old, having been proposed by Greenwood and Yule in 1915 for inactivated whole-cell cholera and typhoid vaccines.

Measuring vaccine efficacy

Vaccine efficacy is best measured by double-blind, clinical trials. These explore the “best-case scenarios” of vaccine protectiveness under controlled conditions and are commonly required before a new vaccine is licensed by the Food and Drug Administration and other global regulatory authorities.

The outcome of efficacy is measured by parameters like - proportionate reduction in disease attack rate (AR) between the unvaccinated (ARU) and vaccinated (ARV) individuals in the clinical trial. This can give the relative risk of getting the disease (RR) of the disease after use of the vaccine.

Efficacy = (ARU-ARV)/ARU X 100

OR

Efficacy = (1-RR) X 100

Advantages and disadvantages of vaccine efficacy

While advantages of knowing the vaccine efficacy means it has been tried in strict clinical conditions, the disadvantages are that it has not been tried on larger general populations. Vaccine efficacy studies can measure outcomes beyond disease attack rates, including hospitalizations, medical visits, and costs.

Vaccine effectiveness and “field efficacy”

Vaccine effectiveness was initially termed “field efficacy”. Essentially, vaccine effectiveness is a “real world” view of how a vaccine reduces disease in a population. This vaccine may already have been proved to be efficacious in clinical trials. This measure can assess the net balance of benefits and adverse effects of a vaccination program rather than the vaccine alone in field conditions.

Vaccine effectiveness

Vaccine effectiveness is proportional to vaccine potency or vaccine efficacy but is primarily affected by how well target groups in the population are immunized, difficulties in storing, administering, cost, accessibility, availability, stability, and manufacturing of the vaccine.

Effectiveness is expressed as a rate difference. It uses the odds ratio (OR) for developing infection despite vaccination and can be derived as:

Effectiveness = (1-OR) X 100.

Considerations for the effectiveness of a vaccine

  • effect of the disease on the local prevalence and incidence of the disease it is targeted against. This needs to be considered over the medium and long term as well
  • continued surveillance for the relevant disease following the introduction of a new vaccine
  • maintenance of high immunization rates, even when a disease has become rare
  • maintenance of availability, adequate stability, low cost, and wide coverage of the vaccine

Further Reading

Last Updated: Feb 20, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2023, February 20). Vaccine Effectiveness. News-Medical. Retrieved on December 07, 2024 from https://www.news-medical.net/health/Vaccine-Effectiveness.aspx.

  • MLA

    Mandal, Ananya. "Vaccine Effectiveness". News-Medical. 07 December 2024. <https://www.news-medical.net/health/Vaccine-Effectiveness.aspx>.

  • Chicago

    Mandal, Ananya. "Vaccine Effectiveness". News-Medical. https://www.news-medical.net/health/Vaccine-Effectiveness.aspx. (accessed December 07, 2024).

  • Harvard

    Mandal, Ananya. 2023. Vaccine Effectiveness. News-Medical, viewed 07 December 2024, https://www.news-medical.net/health/Vaccine-Effectiveness.aspx.

Comments

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment
Post

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Innovative vaccine shields livestock from four strains of foot and mouth disease