EFFICACY RATE IN VACCINES

EFFICACY RATE IN VACCINES

Subject :Science& tech

Context: Different pharmaceutical companies are now coming out with the success stories of their potential vaccines, and the efficacy rates of these vaccines are reported to be high – 70%, 90%, 95%, and so on.

Concept:

• ‘Vaccine efficacy’ is defined to measure whether the vaccine is able to prevent the disease significantly or not, and if so, to what extent.
• Vaccines are usually approved on the basis of results from three stages of clinical trials. The trials aim to assess short-term safety, ability to generate an immune response, and efficacy

How Efficacy is calculated?

• Phase III trial, which is often the most elaborate one, investigates the efficacy of the vaccine under trial – usually in comparison to a placebo, which maybe a similar-looking injection having no medical effect.
• In a phase III trial, often thousands of people are given the vaccine or a placebo, and then these people are monitored over several months to see whether the people receiving the vaccine get infected at a lower rate than people who get the placebo, on average.
• Thus, the performance of the vaccinated group is compared to that of the unvaccinated group.
• Vaccine efficacy is expressed as a proportionate reduction in disease attack rate, AR, between the unvaccinated, (ARU) and vaccinated, ( ARV) groups under the phase III trial.
• The ratio of ARV to ARU is called the risk ratio,(RR). A lower value of RR clearly indicates better performance of the potential vaccine.
• When both the vaccinated and unvaccinated groups have, more or less, equal number of individuals, RR is the simple ratio of the number of infected in the vaccine group to that in the placebo group.
• And, one minus RR, expressed in percentage, is called the “Vaccine Efficacy”.