Covid-19: How effective is a third vaccine dose?

The turning point came just after 6:30 on a Tuesday morning.

It was the 9 December 2020 and 91-year-old Margaret Keenan and 81-year-old William Shakespeare – who delighted the world by hailing from Warwickshire, like the poet – had just become the first people to ever receive an initial dose of a Covid-19 vaccine outside clinical trials.

The entire room burst into applause. The day was named "V-day", and the atmosphere was giddy. One British newspaper celebrated with the whimsical headline "The taming of the flu" – while footage of a particularly charismatic...