People aged over 50 are being asked to book their coronavirus jabs now or risk losing their slots due to supply concerns.
National medical director Professor Stephen Powis is calling on anyone who qualifies for the Covid vaccine but has not yet received a first dose to book an appointment in the coming days.
The NHS is expecting a slowdown in UK vaccine supply for the whole of April, meaning medics will concentrate on second doses, with fewer first appointments available, reports The Mirror.
NHS England has said no first appointments should be booked for people under the age of 50 unless they fall into a higher priority group, such as those who are clinically vulnerable.
Prof Powis said: "It is a testament to the careful planning and sheer hard work of staff that the NHS vaccination programme is continuing to protect people against coronavirus at a record pace.
"I was thrilled to get my first dose earlier this month, it was quick, painless and safe and it feels great knowing I've got protection against Covid-19 - so if you are eligible, do not delay, book a jab."
A shortage in the supply of the vaccine has hit the UK's mass vaccination drive.
Part of the problem comes from a shortfall in AstraZeneca doses of the jab, which the UK had ordered from the Serum Institute of India, and have been delayed.
Half of the 10 million expected doses from India were delivered this month.
Local health bodies have been told to focus efforts in April on the top priority groups 1 to 9 - which means all over-50s or vulnerable groups.
An NHS letter, signed by Dr Nikita Kanani, medical director for primary care for the NHS in England, said vaccination centres should close unfilled bookings from March 29.
It added that no further appointments should be uploaded to the National Booking System or Local Booking Systems in April.
Supplies of the vaccine are set to improve from May and the Moderna jab - a third approved by the UK regulator - will later arrive in the UK.
Around seven in 10 people aged 50 to 54 have now had a first dose of a vaccine, according to NHS England.
This equates to 28.6 million people across the UK who have been given their first jab, while 2.5 million have had the second dose.
Anybody aged 50 or over can book themselves in for a first dose before March 29 online using the national booking system for England.
People aged 18 and over who are clinically vulnerable should also book themselves in for a vaccine.
GPs will continue contacting eligible patients on their lists and offering vaccines to anyone who has not had one so far.
