What is a Covid-19 booster shot? And who should get it?

Many governments around the world have started issuing policies regarding the roll out of Covid-19 booster shots. They’re an additional dose of a vaccine given to people who have already received their initial doses. While experts are still unsure exactly how long the protection against Covid-19 the initial shots provide, they agree that a booster does help raise immunity responses. However whether booster shots should be given beyond the immunocompromised at this stage of the pandemic is still a matter of debate between some experts and politicians. The South China Morning Post takes a look at booster shots, what they do, why we need them and when they should be given.