The government met its target of offering a vaccine to its top four priority groups - the equivalent of 15 million people by February 15 on Sunday.
There are around 67 million people in the UK, meaning just under a quarter of the population has received the first dose since the first one was given on December 8.
The milestone adds to the positive news from Friday when it was confirmed the Covid-19 reproduction number, R rate, had fallen below 1 for the first time since July.
Who has been vaccinated so far?
People in the UK the top four priority groups have been offered the first coronavirus vaccine dose, these are:
1. care home residents and their carers - 800,000 people2. people over the age of 80 and frontline health and social care workers - 7.1 million people3. people aged 75 to 79 - 2.3 million people4. people aged 70-74 and those deemed to be “clinically extremely vulnerable” - 4.4 million people
The clinically extremely vulnerable includes those who:
have had an organ transplant
are having chemotherapy or antibody treatment for cancer
are having an intense course of radiotherapy for lung cancer
have blood or bone marrow cancer, e.g. leukaemia, lymphoma or myeloma
have had bone marrow or stem cell transplants in the last six months or who are still taking immunosuppression drugs
have cancer treatments that can affect the immune system, e.g. protein kinase inhibitors or PARP inhibitors
have severe respiratory conditions, e.g. cystic fibrosis, severe asthma and severe chronic obstructive pulmonary disease.
have diseases that significantly increase the risk of infections, e.g. severe combined immunodeficiency and homozygous sickle cell disease
are on immunosuppression therapies sufficient to significantly increase risk of infection
have a problem with their spleen or their spleen has been removed
are an adult with Down's syndrome
are an adult who is having dialysis or has severe (stage 5) long-term kidney disease
have a serious heart condition and are pregnant
anyone else classed as clinically extremely vulnerable, based on GPs' judgement
The second dose of the jab can be delayed between four and 12 weeks. This means people receiving their jab today will get their second vaccine by May.
Who will be offered the vaccine next?
On Friday, the government announced that people aged 65 to 69 and those who are clinically vulnerable will be invited to book their jab.
The vaccine will now be rolled out across the next five priority groups:
5. people aged 65 to 69 - 2.9 million people6. people aged 16 to 64 with underlying health conditions which put them at higher risk of serious disease and death - deemed as "clinically vulnerable" - 7.3 million people7. people aged 60 to 64 - 1.8 million people8. people aged 55 to 59 - 2.4 million people9. people aged 50 to 54 - 2.8 million people
The clinically vulnerable group includes those who:
have a severe lung condition (such as severe asthma, COPD, emphysema or bronchitis). Severe asthma is defined as those who require continuous or repeated use of systemic steroids or with previous exacerbations requiring hospital admission.
have heart disease (such as heart failure)
have chronic kidney disease (such as kidney failure)
have chronic liver disease (such as hepatitis)
have a blood cancer (such as leukaemia, lymphoma or myeloma)
have a condition affecting the brain or nerves (such as Parkinson's disease, motor neurone disease, multiple sclerosis or cerebral palsy)
lowered immunity due to disease or or treatment (such as HIV infection, steroid medication, chemotherapy or radiotherapy)
have rheumatoid arthritis, lupus or psoriasis (who may require long term immunosuppressive treatments)
have a condition that means they have a high risk of getting infections
have had an organ transplant
have had a stroke or transient ischaemic attack (TIA)
a problem with your spleen (such as sickle cell disease or coeliac syndrome) or you have had your spleen removed
are very obese (a BMI of 40 or above)
are severely mentally ill (such as schizophrenia or bipolar disease)
have a severe or profound learning disability
The clinically vulnerable group includes people with similar but less severe conditions compared to those in the clinically extremely vulnerable group.
The government plans for everyone in the top nine groups to be offered their first dose of the vaccine before May.
Parts of the UK have already started vaccinating the over-65s after reaching everyone in the top four priority groups.
In England, Nottinghamshire Clinical Commissioning Group had already invited over-65s to receive a vaccine, while in Shropshire, Coventry and Hampshire some vaccines have been given.
In Wales, First Minister Mark Drakeford said some over-50s there have already begun to be contacted about vaccines.
Matt Hancock tells ITV's Good Morning Britain about the next steps for the Covid vaccine rollout:
In Scotland, First Minister Nicola Sturgeon said she expects many in the 65-69 age group to have had their first vaccine by the middle of this month.
In Northern Ireland, people aged 65-69 have been able to book a Covid-19 vaccine at seven regional centres since the end of January.
Although the impact of the vaccination programme will not be immediately felt in the NHS, it has been estimated that vaccinating the top nine priority groups the jab will reduce deaths by up to 99%.
How many people will have had the jab after the second phase?
Under the second phase of the rollout, 17 million more people will get the jab - all those in priority groups 5 to 9.
This means that by the end of the second phase, 32 million people should have been offered to have the vaccine - nearly half of the UK population.
What about keyworkers and other adults?
The Joint Committee on Vaccination and Immunisation (JCVI) has not yet set out plans for key workers. It expects to set out recommendations for future plans by the end of the month.
Health Secretary Matt Hancock has promised that all UK adults will be offered a Covid vaccine by autumn.
Can I meet other people after having the jab?
Not yet. It takes time for the body to build up immunity after the jab, and it is important to get the second jab to get the full protection.
Besides, it is not yet known whether the vaccines can stop people from transmitting the virus. And there are questions over how protective they are against new variants.
What should I do if I haven't received an offer for the jab yet, despite being in the top nine priority groups?
You can book through the website www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/book-coronavirus-vaccination
Or you can call 119.