Back in March, when the coronavirus pandemic was starting to sweep the globe, a vaccine couldn’t come quickly enough.

Now, with a locally developed vaccine showing promising results and several overseas candidates in phase 3 clinical trials — the last big hurdle before they could be approved by regulators and available to the public — some people are surprised at the speed at which they’ve been developed.

Previous vaccines have taken years to develop. Some diseases we’ve never found a vaccine for.

So how come scientists have been able to fast-track the process to get them ready so quickly? Will they be safe to use?