A schoolboy who flicked a small piece of cheese at a fellow pupil causing a fatal allergic reaction was “childish and thoughtless”, but his actions were not “calculated” to cause serious harm, a coroner has ruled.

Karanbir Cheema, 13, who also had allergies to wheat, gluten, egg, milk and tree nuts, suffered from severe reaction at his school in west London on June 28 2017.

He was taken to hospital in a life-threatening condition but died almost two weeks later with his parents by his side at Great Ormond Street Hospital on July 9.

On Friday, coroner Mary Hassell said the case of Karanbir, known as Karan, was “extremely rare”, but she absolved the boy who threw the cheese of intending to seriously hurt the youngster.

The inquest heard a pupil, who cannot be identified because of his age, took a 2cm x 2cm piece of cheese from a friend’s baguette at the end of morning break-time and flicked it at Karan, triggering the “unprecedented” reaction.

Karan immediately attended first aid as his condition quickly worsened, as he became breathless, and scratched vigorously at his skin.

The coroner said: “He pulled his shirt off, screamed and flung himself around the room in panic. He could not breathe.”

He later suffered a cardiac arrest and was taken to hospital, but he suffered a serious brain injury due to a lack of oxygen and died almost two weeks later.

Recording a narrative verdict at St Pancras Coroner’s Court on Friday, Hassell said: “I think this was a thoughtless act – and I mean that in exactly that sense.

“He (the boy) was simply not thinking.

“This was a childish and thoughtless act but was not calculated to cause serious harm.”

But the coroner said there was a “missed opportunity” at William Perkin school where Karan studied to apprise pupils of the severity of his “grave allergies”.

She said additional factors contributing to his death included his poorly controlled asthma, the fact his allergy action plan was not included in the school’s care plan or medical box, and that the school healthcare provision for Karan was “inadequate”.

Hassell said there was a “national lack of understanding” around the correct use of an EpiPen, which contains adrenaline and was administered at the school to Karan but only following a delay.

The equipment was nearly a year out of date, the inquest heard last week, but she said it was not possible to say whether having adrenaline that was in date would have changed the outcome.

The coroner said she would prepare a report intended to prevent future deaths, sent to Karan’s school, emergency services, government departments and experts, highlighting her concerns about Karan’s care in the run-up to his death.

Speaking after the inquest, the 13-year-old’s mother Rina Cheema said: “I think it would help a lot of children out there, whatever happened to my son, if the schools, the institutions, hospital, paramedics, (were) to become aware how serious allergies are.

“My son was mature, he knew himself how fast to react. His words were at school: ‘please help me or I’m going to die’. That says it all.”

Asked how she felt since his death, she replied: “Lonely. He was my best friend, my soulmate.”

Specialist allergy doctor Adam Fox last week told the inquest into the death that he believed the “unprecedented” case was the only time someone has died from anaphylaxis through skin contact alone.

Dame Alice Hudson, executive headteacher of the Twyford Trust, encompassing William Perkin school, said: “It’s my view that there was a very good general awareness of his allergies in relation to both bread and cheese.

“From my experience in interviewing the students I would say they did have that awareness and were being very careful about what they said.

“It may be them trying to support themselves from something that would be very painful to admit.”

Karan, who also suffered from eczema, was reported to have scratched at his neck so much that blood was visible, with Dr Fox saying: “Further scratching and degrading of the skin barrier could have led to further contact.”

Other factors making him more likely to have a severe reaction were being male, of Asian origin, a teenager, and having hayfever, he added.