Vaccine efficacy is the percentage reduction in disease incidence in a group of people who received a vaccine in a clinical trial. (Image: News18 Creative)
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During the phase 3 trials a large group of volunteers is given the vaccine, and another group is given a placebo. Scientists look at the difference in new cases between the two groups i.e., the one that received the vaccine being investigated vs the one injected with a placebo. (Image: News18 Creative)
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It means, 77.8 percent reduction in new cases of the disease in the vaccine group compared with the placebo group. (Image: News18 Creative)
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Covaxin was approved for restricted use in an emergency situation by the Drug Controller General of India on January 3. The approval was without efficacy data. (Image: News18 Creative)
Vaccine effectiveness measures how well a vaccine works when given to people in the community outside of clinical trials (i.e., less than perfectly controlled conditions). (Image: News18 Creative)
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Many vaccines have very high levels of effectiveness but very few are 100 percent effective. (Image: News18 Creative)
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Vaccine efficacy (and effectiveness) numbers help scientists determine how many people need to be vaccinated to reach herd immunity. (Image: News18 Creative)
