Some doctors' practices in England will be able to offer the Covid-19 vaccine developed by AstraZeneca and the University of Oxford from Thursday, the National Health Service said.
The plan is to have the majority of the country's most vulnerable vaccinated within six weeks.
More than 1.3 million people in the UK have received one shot of AstraZeneca or Pfizer-BioNTech's Covid-19 vaccine.
"We are aiming to offer vaccinations to the majority of care home residents by the end of January and all 13 million people in the top four priority by mid-February," Health Secretary Matt Hancock said.
The government must increase shots to about 2 million a week to hit its target.
Top priority groups include care home residents, the elderly, the clinically vulnerable, and frontline health and social-care workers.
Prime Minister Boris Johnson said that if the vaccine introduction went to plan, lockdown measures introduced this week could start to be eased in February.
AstraZeneca's vaccine will be provided to some GP services, the NHS said, after it was first administered in hospitals on Monday.
Another 180 GP-led vaccine services are coming online this week, with up to 100 more hospital sites.
That is on top of 700 sites that were already distributing the Pfizer vaccine after its approval last month.
AstraZeneca's vaccine does not have the ultra-low temperature requirements that Pfizer's does, making it easier to store.
Initial boxes of the Pfizer vaccine contained nearly 1,000 doses, but the NHS said that smaller boxes had also been approved, which could be used in settings such as care homes without wasting doses.
Britain is giving priority to providing first shots to as many people as possible to offer some protection, delaying second doses for up to 12 weeks.
While some doctors have queried the move, England's chief medical officer, Prof Chris Whitty, on Tuesday said the balance of risk supported it.
