Britain has offered all over-50s a first dose of COVID-19 vaccine, hitting a target to offer injections to all people in its nine highest priority groups by April 15.

Britain has had one of the world’s quickest vaccine rollouts, behind only Israel in the proportion of population receiving at least one dose.

The government said on Tuesday it had offered at least one shot to priority cohorts 1 to 9, which include all adults over 50, the clinically vulnerable, and health and social care workers, ahead of Thursday’s deadline.

“We have now passed another hugely significant milestone in our vaccine program by offering jabs to everyone in the nine highest risk groups,” Prime Minister Boris Johnson said.

“We will now move forward with completing essential second doses and making progress towards our target of offering all adults a vaccine by the end of July.”

The success of the program has underpinned Mr Johnson’s roadmap out of lockdown. On Monday, all shops and outdoor hospitality settings in England were allowed to re-open.

But Britain has slowed the pace of first doses to ensure people in high-priority groups receive a second dose despite lower vaccine supplies in April than March.

Mr Johnson’s office said the government remained on track to offer all adults a shot by July 31.

People in their late 40s are expected to be the next to be invited for shots, though a final decision has not been made, his office said.

The Joint Committee on Vaccination and Immunisation has previously said it expects to continue an age-based approach to the rollout rather than prioritising people based on occupation or other risk factors.

Last week the JCVI also said it advised alternatives to AstraZeneca’s vaccine for those under-30, given a very rare possible side effect of blood clots and the age group’s low risk from COVID-19.