Jo Whiley has said she is living a "nightmare" after she was offered the coronavirus vaccine before her sister who has learning difficulties and diabetes.
The BBC Radio 2 DJ has been campaigning for her younger sister, Frances, who has the rare Cri du Chat genetic syndrome, to be prioritised for the jab.
The 55-year-old said people with learning disabilities are often neglected by society and that she would give up her vaccine "in a heartbeat" if she could.
Appearing on BBC Radio 4's Today programme, Whiley said the care home where Frances, 53, is a resident had suffered an outbreak of Covid-19 last week and the effect on her sister's mental health had been "quite extreme".
She said: "Oh my God, I can't tell you how frustrating it is and how horrendous it is.
"It is the stuff of nightmares at the moment. I feel like I am living through a nightmare.
"All weekend it has been awful - really, really difficult. It has been hard for my parents, it has been hard for everyone in the care home, and it continues.
"And then, ironically, I got a message to say I was due to have my vaccine before my sister who has got learning difficulties and underlying health conditions. Go figure."
Since the interview, Whiley has been told that Frances has tested positive for the virus, the BBC reported.
Frances has been unable to see her parents since the outbreak and become "very distressed".
Whiley said she has, for the first time, refused to take calls from family members.
More than 15 million people in the UK have received their first dose of a Covid vaccine, just over two months since the first jab was administered.
The NHS initially targeted the top four priority groups, including people over the age of 70 and health and care staff, aiming to offer the jab to everyone in this group by mid-February.
Whiley said she does not know why has been called for her injection, but suggested it may be because she is classed as a carer for her sister.
"I fail to understand, to be honest with you," she told the programme.
"Myself, my parents and the home have done everything we can to try and facilitate the vaccine coming in to the people who need it the most.
"She is in tier six but she also has quite bad diabetes, which in my understanding puts her in tier four because she has an underlying health condition, so I would have thought that she would have been vaccinated, but that hasn't happened.
"And I suppose what I am doing is just wanting to speak up for people like Frances, people who live in her care home, who have been overlooked, because this happens so often.
"People with learning difficulties are neglected. They haven't got a voice, they haven't got anybody there. Just badgering everybody saying 'What about me? Help me out here'."
Whiley said her mind is "boggling" over why she has been called for her jab.
She added: "And I would give up my vaccine in a heartbeat if I could for my sister and any of the residents in her house to have their vaccine. It just does not feel right."