GP leaders have criticised a decision to delay giving the second dose of Covid-19 vaccines, saying the move will cause huge problems for thousands of partially-vaccinated elderly and vulnerable people.

As the approval of the Oxford/AstraZeneca vaccine was announced on Wednesday, a new dosing regimen was outlined, aimed at providing a speedier rollout.

Experts advising the Government, including the Joint Committee on Vaccination and Immunisation (JCVI), said that the focus should be on giving at-risk people the first dose of whichever vaccine they receive, rather than providing the required two doses in as short a time as possible.

This now means the second dose of both the Oxford/AstraZeneca and the Pfizer/BioNTech vaccines will be within 12 weeks of the first.

GPs have now warned the regimen change will affect tens of thousands of elderly and vulnerable patients who were due to get their second dose of the Pfizer jab in the coming days and weeks, and will need to be rebooked.

Chair of the British Medical Association’s (BMA) GP committee, Dr Richard Vautrey, said: “It is grossly and patently unfair to tens of thousands of our most at-risk patients to now try to reschedule their appointments.

“The decision to ask GPs, at such short notice, to rebook patients for three months hence, will also cause huge logistical problems for almost all vaccination sites and practices.

“For example, to make contact with even just two thousand elderly or vulnerable patients will take a team of five staff at a practice about a week, and that’s simply untenable.”

Dr Vautrey said the BMA would support practices who honour the existing appointments for the follow-up vaccination, calling for the Government to do the same.

He added: “The Government must see that it’s only right that existing bookings for the oldest and most vulnerable members of our society are honoured, and it must also as soon as possible publish a scientifically-validated justification for its new approach.”

The criticism comes after Pfizer said that it only assessed its vaccine on a two-dose regimen where people were given the jab three weeks apart, and there was “no data to demonstrate that protection after the first dose is sustained after 21 days”.

Speaking at a Downing Street briefing on Wednesday, Prof Wei Shen Lim, chairman of the JCVI, said that with Covid infection rates currently at a high level, the “immediate urgency is for rapid and high levels of vaccine uptake”.

He added: “This will allow the greatest number of eligible people to receive vaccine in the shortest time possible and that will protect the greatest number of lives.”

Speaking at the same briefing, Professor Sir Munir Pirmohamed, chairman of the Commission on Human Medicines expert working group on Covid-19 vaccines, added: “Because of the design of the trial, some people got second doses at different time intervals.

“This allowed an analysis of the effectiveness of the vaccine if you were to be able to delay between four to 12 weeks.

“This showed that the effectiveness was high, up to 80%, when there was a three-month interval between the first and second doses, which is the reason for our recommendation.”