The UK has become the first country in the world to approve the Pfizer/BioNTech coronavirus vaccine for widespread use.
British regulator, the MHRA, says the jab, which offers up to 95% protection against Covid-19 illness, is safe for roll out.
Immunisations could start within days for people in high priority groups.
The UK has already ordered 40m doses – enough to vaccinate 20m people, with two shots each.
Around 10m doses should be available soon, with the first doses arriving in the UK in the coming days.
It is the fastest ever vaccine to go from concept to reality, taking only 10 months to follow the same developmental steps that normally span a decade.
Although vaccination can start, people still need to remain vigilant and follow coronavirus rules to stop the spread, say experts.
That means sticking with the social distancing and face masks, and testing people who may have the virus and asking them to isolate.
What is the vaccine?
It is a new type called an mRNA vaccine that uses a tiny fragment of genetic code from the pandemic virus to teach the body how to fight Covid-19 and build immunity.
An mRNA vaccine has never been approved for use in humans before, although people have received them in clinical trials.
The vaccine must be stored at around -70C and will be transported in special boxes, packed in dry ice. Once delivered, it can be kept for up to five days in a fridge.
Who will get it and when?
Experts have drawn up a provisional priority list, targeting people at highest risk. Top are care home residents and staff, followed by people over 80 and other health and social care workers.
They will receive the first stocks of the vaccine – some as soon as next week. Mass immunisation of everyone over 50, as well as younger people with pre-existing health conditions, can happen as more stocks become available in 2021. It is given as two injections, 21 days apart, with the second dose being a booster.