Over 50s and the most vulnerable can expect to get their second shot eight weeks after their first.
This shortens the interval time between doses by three weeks.
The decision to accelerate second doses to over 50s and most vulnerable was guided by advice from the Joint Committee on Vaccination and Immunisation (JCVI), the body advising the government on the vaccine rollout.
The PM acknowledged that there are “important unknowns” at this stage, but “if it is only marginally transmissible, we can continue as planned”.