Vaccine bosses insist there is no need for Northamptonshire patients to be offered 'mix and match' Covid-19 jabs.
Those in charge of the county's rollout insist there is no shortage of supplies and everybody should be given a second dose from the same vaccine as their first.
More than 157,000 people had both doses of either the Pfizer-BioNTech or Oxford-AstraZeneca vaccines by May 2, according to NHS figures, after another 31,000 jabs were delivered in the county during the last week.
Chris Pallot, Northamptonshire's Covid-19 Vaccination Programme director, said different jabs may be given only for very rare clinical reasons.
He added: “There are very strict criteria in place around the administering of second vaccine doses, which all vaccination services are required to adhere to.
"Everyone should receive the same type of vaccine for their second dose as they did for their first and we have enough supply of all the relevant vaccine types in Northamptonshire.
"Only in very rare medical circumstances should a different vaccine be administered for a second dose, and only then after a conversation with the patient’s clinician.
“If you are in a priority group and haven’t yet received your first dose or missed your appointment for your second dose, please contact your GP practice, call 119 or visit www.nhs.uk/covidvaccination.”
The statement came after advice from some surgeries appeared to suggest patients waiting for a second Pfizer jab could be offered the AstraZeneca vaccine. Those posts have since been removed.
But Mr Pallot's advice to anyone approaching 12 weeks after their initial jab to get in touch.
He added : "Northamptonshire has enough vaccine available for everybody in the priority groups and for second doses.
"My advice is if you're approaching the period of time when you're expecting to hear from your GP, at around week 11, and you've got any concern please call your practice.
"Please don't call any earlier because they are really busy and doing their best to call everyone.
"We will ensure there is a safety net in place for anyone who has not been able to attend their appointment for a second dose for whatever reason.
"All our GPs know how to access support if there's an issue with giving that appointment."
The vaccine rollout has been a huge success in Northamptonshire with 530,765 doses delivered and around 373,000 people having had at least one jab of either Pfizer or AstraZeneca — or the Moderna vaccine which has been available here since early-April.
The Joint Committee on Vaccine and Immunsation recommends giving patients booster jabs with the same vaccine as their first, although it adds: "It is reasonable to offer one dose of the locally available product to complete the schedule if the same vaccine used for the first dose is not available.”
Studies started in February into combining different vaccines for the two doses but the first results are not expected until June or July.
Health experts are understood to generally agree that mixing vaccines should be safe, although the University Oxford Com-Cov trial is looking into how well it works and common vaccine reactions.
Public Health England's head of immunisations, Dr Mary Ramsey, also said earlier this year: “Every effort should be made to give the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all.”