A mother whose two-year-old son spent five days in hospital fighting a severe case of chickenpox has called for anyone who wants them to get vaccinations on the NHS against the disease.

Sarah Allen urged ministers to rethink eligibility for immunisation, under which only those looking after children with a weakened immune system, for example because they are undergoing chemotherapy, can receive it.

Allen, a nursery manager in Cambridgeshire, spoke out after doctors said her son Jasper’s chickenpox was the worst case of the usually mild illness they had ever seen. The toddler became so ill last month that staff at Hinchingbrooke hospital in Huntingdon, Cambridgeshire, put him on an intravenous drip and gave him antibiotics, antiviral drugs and morphine.

Allen claims that Jasper was initially denied treatment when her GP practice refused to let her see a doctor. “When I first called our local GP’s surgery, I spoke to the receptionist to make an appointment for Jasper, but when I told her it was chickenpox, she said to me, ‘Every mother thinks their child has bad chickenpox.’ I knew I wasn’t being a neurotic mother. I have two children and have run a nursery and seen hundreds of kids with chickenpox before, so I knew this wasn’t normal.

“When Jasper was admitted to hospital, it was scary, but I was also relieved I was actually being taken seriously and that they were doing something about it. We couldn’t hold him for three days because he screamed every time we touched him.” Jasper’s chickenpox was so severe that he has had scans of his heart to ascertain whether he has suffered any long-term damage as a result, she added.

Immunisation against the disease is not part of the government’s childhood vaccination programme. Jabs are given only to adults and children who are in close contact with someone who is either immuno-suppressed or would otherwise be at risk if they got chickenpox.

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Public Health England, which oversees NHS vaccination schemes, indicated that no change of policy was imminent. A spokesman added: “The expert advisory body the Joint Committee on Vaccination and Immunisation is currently undertaking a review of a childhood vaccination programme against chickenpox in the UK, based on the available scientific evidence, including consideration of the cost-effectiveness of any programme. This review is likely to be concluded next year.”

Cambridgeshire Community Services NHS Trust, which runs the children’s inpatient ward at Hinchingbrooke, where Jasper was treated, said in a statement that: “We can confirm Mrs Allen’s statement that Jasper Allen was treated on our children’s inpatient ward for five days with a severe case of chickenpox.”

Cambridgeshire and Peterborough clinical commissioning group, which oversees GP services in the area, said it could not comment on any individual patient’s treatment. It has not received a complaint from Allen about her local GP surgery refusing her an appointment. In a statement, it said: “Chickenpox is usually a mild illness from which most children recover on their own. Symptoms include a high temperature, aches and pains, and a rash of blisters. These usually pass within a week or two, and the blisters dry up and fade.

“The best treatment is to use soothing creams and/or appropriate doses of paracetamol to ease any discomfort, while keeping your child hydrated by giving them lots to drink.

“It is highly advisable that parents and carers keep a watchful eye on children who have chickenpox, as complications, although rare, can develop, especially in children who are very young, are on other medications, or who may have a weakened immune system.”