Over-50s and those at risk should book their Covid-19 vaccines quickly before slots run out, the national medical director for the NHS has said.
The UK vaccine rollout out is expected to slow in the coming month due to a shortage of supply.
With supply squeezed, the NHS will concentrate on delivering second doses, meaning there will be fewer first appointments available.
Anyone who qualifies for a jab but has not yet received a first dose are advised to book an appointment in the next few days, Professor Stephen Powis urged.
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.
Around seven in 10 people aged 50 to 54 have now had a first dose of a vaccine, according to NHS England.
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.
Phase one priority groups (to be offered first dose by mid-April)
1 - Residents in a care home for older adults and their carers (800,000 people)
2 - Those aged 80 and over and frontline health and social care workers (a total of 7.1 million people in this group: 3.3m over 80s, 2.4m healthcare workers, 1.4m social care workers)
3 - Those aged 75 and over (2.3 million)
4 - Those aged 70 and over and clinically extremely vulnerable individuals (4.4 million)
5 - Those aged 65 and over (2.9 million)
6 - All individuals aged 16 to 64 with underlying health conditions which put them at higher risk of serious disease and mortality (7.3 million)
7 - Those aged 60 and over (1.8 million)
8 - Those aged 55 years and over (2.4 million)
9 - Those aged 50 years of age and over (2.8 million)
Phase two (to be offered first dose by mid-July)
10 - All those aged 40-49 years
11 - All those aged 30-39 years
12 - All those aged 18-29 years
GPs will continue contacting eligible patients on their lists and offering vaccines to anyone who has not had one so far.
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.”