New Delhi: As the coronavirus pandemic continues to rage across the world, there is growing impatience for an effective vaccine. Unlike during the beginning of the pandemic, now many pharma companies and research institutes have progressed in their vaccine development programmes. Two companies the US-based Moderna and Pfizer have announced that their vaccine candidate has shown over 90 percent effectiveness.

While Moderna has said that it's 94.5 percent effective in preventing Covid-19, Pfizer Inc and German biotech company BioNTech BNT162b2, today announced their mRNA-based vaccine 90% effective in preventing the infection.

No vaccine is 100% effective, a small percentage of people are not protected after vaccination and for others the protection may wane over time.

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What is vaccine effectiveness?

During the development of a vaccine, it is tested on various parameters including its efficacy and effectiveness. These are measures that compare the rates of disease between vaccinated and unvaccinated people. The effectiveness of a vaccine is measured once it is approved for use in the general population that is in real-world situations as compared to efficacy which is measured in a controlled environment. Several factors can impact vaccine effectiveness such as age, comorbidity, mode of vaccine delivery, and also if the vaccine is matching the microbial strain that is circulating at the time.

A report by AFP says that effectiveness numbers will change as the vaccine studies continue since the early calculations were based on fewer than 100 Covid-19 cases in each study. But early results provide strong signals that the vaccine could prevent a majority of disease when large groups of people are vaccinated.