All people with underlying health conditions are currently being offered COVID vaccines but as a key indicator of being at risk of coronavirus, how has the government defined such a broad group?
People with underlying health conditions are thought to be the largest group on the government's vaccine priority list – accounting for about 7.3 million people.
On Wednesday, the government expanded it by a further 150,000 when it decided to offer everyone on the GP Learning Disability Register a vaccine as a priority.
The decision in part was driven by BBC presenter Jo Whiley who questioned why she was offered the vaccine before her 53-year-old sister, who has the rare Cri du chat genetic syndrome.
Watch: People with learning disabilities 'six times more likely to die from Covid-19'
All people with the most severe learning disabilities had already been included in the priority group but fears of regional inequalities after local medical groups were given the power to decide what made someone vulnerable.
The Joint Committee on Vaccination and Immunisation said GP systems may not always capture the severity of someone’s disability, meaning some adults more severely affected by learning disabilities may not have been previously invited along with others in group six.
A report by Public Health England in November found that people with learning disabilities were up to six times more likely to die with coronavirus.
Whiley said she was "grateful to the government for listening, because it’s a very complicated situation and it’s very difficult to categorise people according to their disability."
There has been a debate over who should be included on the list, and the government recently used a new system of comparing lots of peoples minor risks to see if combined it would put them at major risk of suffering from COVID-19.
This led to the shielding list almost doubling in size as two million more people were identified as "high risk".
The government has already offered a vaccine to all of the original group of shielders who were defined as "extremely clinically vulnerable" and were part of priority group four.
The people on this list suffered from conditions like lung cancer, chronic kidney disease, heart disease or severe respiratory conditions.
The list also included people with some learning disabilities known to have a severe impact on a person's health, like Down's syndrome.
The wider priority group six which includes all people with underlying health conditions includes issues like diabetes and dementia.
The government defines an at-risk underlying health condition as someone something from:
a blood cancer (such as leukaemia, lymphoma or myeloma)
a heart problem
a chest complaint or breathing difficulties, including bronchitis, emphysema or severe asthma
a kidney disease
a liver disease
lowered immunity due to disease or treatment (such as HIV infection, steroid medication, chemotherapy or radiotherapy)
rheumatoid arthritis, lupus or psoriasis (who may require long term immunosuppressive treatments)
have had an organ transplant
had a stroke or a transient ischaemic attack (TIA)
a neurological or muscle wasting condition
a severe or profound learning disability
a problem with your spleen, example sickle cell disease, or you have had your spleen removed
are seriously overweight (BMI of 40 and above)
are severely mentally ill
The government is still working through the priority list but has offered vaccines to the top four groups and has committed to offering them to everyone in the top nine groups by the middle of April.
The whole priority list is:
Residents in a care home for older adults and staff working in care homes for older adults
All those 80 years of age and over and frontline health and social care workers
All those 75 years of age and over
All those 70 years of age and over and clinically extremely vulnerable individuals (not including pregnant women and those under 16 years of age)
All those 65 years of age and over
Adults aged 16 to 65 years in an at-risk group
All those 60 years of age and over
All those 55 years of age and over
All those 50 years of age and over
The vaccine rollout is key to the government's plan to lift lockdown and has set a target in England to end social distancing by 21 June.
Professor Jonathan Van-Tam backed the timetable set out in the road map for easing restrictions and rejected calls for it to be accelerated on Wednesday.
“The government has laid out a pretty careful and pretty painstakingly cautious – but I think appropriate – road map to get us from where we are now to get us in stages – measured, careful stages – to where we want to be in the summer,” he told Sky News.
Watch: How England will leave lockdown