We hear about vaccine “efficacy” ratings, but what do these numbers really mean? You would assume that Pfizer-BioNTech’s 95 per cent efficacy rating and Moderna’s 94 per cent must make them better vaccines than AstraZeneca at 76 per cent or Johnson & Johnson Janssen at 66 per cent.
But that’s not so, and here’s why.
The efficacy rating is a number used to reflect how many individuals were infected during clinical trials using tens of thousands of participants divided into a placebo group (no vaccine) and a group given the vaccine. The calculation used to determine efficacy is the same for all vaccines. However, there is no way to compare vaccines one-to-one based on an efficacy rating, because the trials were held at different times and in different parts of the world, with different sets of data collected, so they don’t share the same comparable conditions.
Pfizer-BioNTech and Moderna were studied primarily in the United States over the summer of 2020, when daily infections were lower than in the late fall and winter period when AstraZeneca and Johnson & Johnson Janssen were studied in Brazil and South Africa. Not only were the daily infections higher in these countries, the cases were of a COVID-19 variant that posed a higher risk of infection.
The efficacy rating is useful to relay what happened during a clinical trial, but it’s not the purpose of a vaccine. The goal of a vaccine is to reduce hospitalization and death, not to prevent any infection at all.
The vaccine that keeps people from serious illness, hospitalization and death is fulfilling its promise. That means
ALL of our COVID-19 vaccines are effective in achieving the objective of preventing serious illness and death.
Waiting for the vaccine you believe to be better based on an efficacy rating only extends the amount of time you, and those around you, are at risk of becoming seriously ill from COVID-19.
Each dose gets us closer to ending the pandemic, so don’t hesitate, vaccinate.
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