Nowadays, there are many different vaccines for COVID-19. They all seem to have different efficacy rates. What does this “efficacy” mean? How is it different from “effectiveness”?
The Pfizer vaccine has a 95% efficacy rate. It is a common misconception that the vaccine’s efficacy rate will protect 95 out of 100 people. This is not the case. Efficacy is determined by small fractions of people in a group who receive the real vaccine while many others (the control group) receive a placebo of the vaccine. For example, Pfizer had 43,661 volunteers enrolled into the observation program. Out of these volunteers, 170 cases were confirmed with COVID-19. So among these confirmed cases, 162 had received a placebo shot, and just 8 had received the real vaccine. The number of people who got sick in the comparison group (who were not vaccinated) was much higher than those of the control group (who were vaccinated). The difference between the two fractions is the efficacy rate. According to Pfizer.com, in South Africa, “where the B.1.351 lineage is prevalent and 800 participants were enrolled, nine cases of COVID-19 were observed, all in the placebo group, indicating vaccine efficacy of 100% (95% CI, [53.5, 100.0]).”
On the other hand, effectiveness is how well a vaccine performs in a real-world environment. It is the more accurate representation of how effective the vaccine is. Therefore, effectiveness cannot be measured in a controlled environment. Many factors affect the effectiveness of a vaccine, including possible underlying health conditions of the patient.
Now you know the difference between a vaccine’s efficacy rate and its effectiveness. Will this affect your choice of vaccine?
See more informaton at:
“Principles of Epidemiology.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 18 May 2012, www.cdc.gov/csels/dsepd/ss1978/lesson3/section6.html.
“What Does Vaccine Efficacy Mean?” Medical News Today, MediLexicon International, www.medicalnewstoday.com/articles/what-is-vaccine-efficacy#Efficacy-versus-effectiveness.
Zimmer, Carl. “2 Companies Say Their Vaccines Are 95% Effective. What Does That Mean?” The New York Times, The New York Times, 20 Nov. 2020, www.nytimes.com/2020/11/20/health/covid-vaccine-95-effective.html.
“Real-World Evidence Confirms High Effectiveness of Pfizer-BioNTech COVID-19 Vaccine and Profound Public Health Impact of Vaccination One Year After Pandemic Declared.” Real-World Evidence Confirms High Effectiveness of Pfizer-BioNTech COVID-19 Vaccine and Profound Public Health Impact of Vaccination One Year After Pandemic Declared | Pfpfizeruscom, www.pfizer.com/news/press-release/press-release-detail/real-world-evidence-confirms-high-effectiveness-pfizer.