Moderna’s first interim analysis of their phase 3 study showed a vaccine efficacy of approximately 95%.
The study enrolled 30,000 participants aged 18 years and older, including some at high risk of severe Covid-19. Half of the participants were given the vaccine while the other half received a placebo.
90 cases of Covid were found in the placebo group, representing an absolute risk of 0.6%. 5 cases were determined in the vaccine group, representing an absolute risk of 0.03%. Therefore, the absolute risk reduction is estimated at 0.57%.
The reported vaccine efficacy of 95% is the percentage reduction in disease incidence in the vaccinated group compared to the unvaccinated group. It is calculated by subtracting the absolute risk in the treatment group from the absolute risk in the control group, and dividing that number by the absolute risk in the control group.
So for the Moderna example it would be as follows:
(0.6% – 0.03%) / 0.6% = 95%
But, as mentioned previously, in absolute terms the risk reduction is just over half of one percent.
It’s still very early but the 95% efficacy is positive news for at risk individuals who are looking forward to the vaccine, and the much smaller 0.57% absolute risk reduction serves as a reminder that the chances of relatively healthy individuals suffering from Covid remains extremely low. In the placebo group of Moderna’s study only 11 people out of 15,000 suffered from a more severe case of Covid, and we don’t have any details yet of their age or pre-existing conditions.
To understand more simply how these numbers are calculated – the difference between relative and absolute risk reduction- I invite you to watch my video “The Absolute Truth About Your Medical Treatment”.
There is still a long way to go for all of the vaccines currently being studied, and years before we have more complete data. For now the most evidence-based long term solution to this crisis remains a healthy plant-based diet, proper exercise, and the acknowledgment that this virus and many others would not exist if it were not for animal exploitation.
Naturopath, Health Educator
Nutrition & Exercise Specialist