Covid-19: What does vaccine efficacy really mean?

India now has four vaccines against Covid-19, with the recent one to be approved for emergency use being the Moderna jab. Moderna has confirmed its shot has an efficacy of 94%. But what does vaccine efficacy really mean then in general? Let us understand this with Moderna's example.

India approved the Moderna jab this week, the fourth Covid-19 vaccine that will be used in the country. Moderna has confirmed its shot has an efficacy of 94 per cent, higher than Covishield, Covaxin, and Sputnik V. But if you think it means 94 out of 100 people who got the US-made jab are protected from Covid-19 infections, you are wrong.