Extent of protection from a disease is ‘Efficacy’

The U.S giant drug maker Pfizer and Moderna has announced about efficacy of 90-95%, another giant drug maker company AstraZeneca has announced efficacy of 60-70% in phase -3 clinical trials. India ‘s drug maker Serum Institute of India (SII) has tie-up with AstraZeneca that has announced 60-70% effective. It’s important to know about the efficacy.

How does efficacy work? What does efficacy means?

According to the experts the extent of protection against particular disease or infection is efficacy of that particular vaccine “The extent of protection from that particular disease is the ‘efficacy’ of the ‘vaccine’. So, for example, if we take two groups of people, say ten thousand in each group, and give one group the ‘vaccine’ injection and the other group a ‘placebo’ (meaning something simple, like normal saline) injection, and then simply follow up the two groups and count the numbers of cases of the disease as they occur. In the first, say, one hundred cases from both groups, if ninety five are in the ‘placebo’ group and only five are from the ‘vaccine’ group, then we could say that the protective efficacy of the ‘vaccine’ is more than ninety percent.” Said Dr Satyajit Rath, Immunologist ,IISER

“The more numbers of disease cases that are counted, the more reliable the evidence becomes. Also, the longer the cases are counted, the better the indication of how long protection lasts. While there is no hard and fast rule about what ‘percentage’ of vaccine efficacy should be considered useful, most people tend to think that fifty percent is a reasonable benchmark.” He added