The COVID-19 pandemic affected human life around the globe and forced healthcare scientists to put the majority of their forces on the development of vaccines against this disease. Currently, researchers are working on the development of vaccines to reduce the number of complications among patients and fight against pandemic. It is necessary to understand the difference between the effectiveness and efficacy and how the last-mentioned indicator can be compared in case of choosing one or another COVID-19 vaccine.
A decision about taking one or another vaccine can encourage high interest in the effectiveness of the injection. However, the science community can hardly study the effectiveness currently. The effectiveness is about the results vaccines have in real life, with all its predictable and occasional factors (WHO). To define the effectiveness, the researchers at first should provide a vaccine to a certain population and then consider the results. Such studies are in progress nowadays, and the currently measured indicator for vaccines is their efficacy. In contrast to effectiveness, which is based on real-life results, efficacy is provided by the outcomes of the clinical studies with controlled environment and outside factors. To understand the efficacy, researchers compare the number of people who got a real vaccine with the ones who got a placebo (WHO). In contrast to effectiveness, efficacy must be measured for all vaccines before they could be used in the wider samples than trials controlled by the supervision of scientists. Following the report published by WHO, vaccines should have at least 50% of efficacy to be used in healthcare institutions. Thus, one can understand the difference between effectiveness and efficacy and the importance of the latter one in the context of COVID-19 vaccines.
The efficacy of substances can be measured by using a few different indicators. One of them is relative risk reduction. This indicator is measured by the difference between rates of attack that occur among people who were vaccinated and those who did not . The studies with the use of relative risk reduction (RRR) showed “95% for the Pfizer – BioNTech, 94% for the Moderna – NIH, 91% for the Gamaleya, 67% for the J&J, and 67% for the AstraZeneca – Oxford vaccines” (Olliaro et al. 1). Another indicator that can be used to define substance efficacy is the absolute risk reduction (ARR). It is defined by the number of people who get an illness while being and not being vaccinated. For this indicator, findings show “1·3% for the AstraZeneca – Oxford, 1·2% for the Moderna – NIH, 1·2% for the J&J, 0·93% for the Gamaleya, and 0·84% for the Pfizer – BioNTech vaccines” (Olliaro et al. 1). Thus, depending on the indicators that are used for efficacy measurement, vaccines can change their place in the list, but it is also worth noting that all of their indicators are quite high.
Therefore, the difference between effectiveness and efficacy is that the first one is based on real-life results, and the second is on the results obtained in a controlled clinical trial under scientists’ supervision. One can measure the efficacy of COVID-19 vaccines using relative risk reduction, absolute risk reduction, or other indicators. Depending on the indicators, different vaccines can become on the top of the list, but all of them have high levels of efficacy.
Olliaro, Piero et al. “COVID-19 Vaccine Efficacy and Effectiveness — The Elephant (Not) in the Room”. The Lancet Microbe, 2021, pp. 1-2. Elsevier BV, doi:10.1016/s2666-5247(21)00069-0.
WHO. “Vaccine Efficacy, Effectiveness and Protection”. Who.Int, 2021, https://www.who.int/news-room/feature-stories/detail/vaccine-efficacy-effectiveness-and-protection.