New guidelines for assessing people with coronavirus who go to hospital were amended after an outcry from parents of children with special needs.
The emergency guidelines are designed to help determine how much treatment a patient will receive.
Those deemed "completely dependent for personal care for whatever reason" will be offered end-of-life care rather than restorative treatment.
This now excludes people with learning disabilities or cerebral palsy.
The Clinical Frailty Score has been published by the National Institute for Health and Care Excellence (NICE) for healthcare workers in England and Wales, but the change was made by the NHS Specialised Clinical Frailty Network.
In a statement NICE said the system was "not perfect" but was designed to support hospital medics "during this very difficult period of intense pressure".
"We welcome the recent clarification that the Clinical Frailty Score should not be used in certain groups," it said.
The updated guidelines now state that it "may not perform as well in people with stable long-term disability" and suggests that it is not used in those cases. It also does not advise that it is used to evaluate children.
The grading assesses a patient's general mobility, fitness and ability to look after themselves.
Those graded "severely frail" are considered unlikely to survive even with medical intervention.
Patients are graded between one and nine, with one being "very fit" and nine being "terminally ill".
NICE suggests those graded between seven and nine can be offered palliative care.
Grade seven is identified as those who are "completely dependent for personal care, for whatever cause".
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Hundreds of parents took to social media to complain.
Donna Jackson from Hampshire is mum to Frankie, who is six and has Down's syndrome.
When she saw the initial guidelines and realised that Frankie would be unlikely to qualify for restorative medical treatment, she set up a petition calling on Prime Minister Boris Johnson to intervene. It received nearly 16,000 signatures in 24 hours.
"I felt physically sick, let down and very emotional," she said.
"Many of our children are immune-suppressed with other health complications, so their chance of catching Covid-19 is high. Why shouldn't they be entitled to the same treatment as any other human?
"My daughter may have Down's syndrome but she brings so much to our world - she is just amazing."
Ms Jackson said she was "over the moon" about the change and intended to remove the petition.
Jackie Sutherland in East Sussex is mum to three children aged between 5 and 11. One child has ADHD and autism, and another has severe learning difficulties.
"When I first saw [the guidelines] I thought it was fake news," she said.
"I went from being sick and tearful to very, very angry very quickly."
Ms Sutherland said she was relieved by the clarification.
"But we parents have had to be so pushy and it shouldn't have come to that," she said.
The charity Mencap called for completely separate guidelines for those with learning disabilities.
"Healthcare professionals should not judge patients on their cognitive ability when making life or death decisions," chief executive Edel Harris said.