Recording a narrative conclusion, Paul Cooper, acting senior coroner for South Lincolnshire, said studies showed there were "significantly raised odds of narcolepsy after [being given the] Pandemrix" vaccine in those aged 18 and above. 

"On the available evidence on the association between vaccination with Pandemrix and onset of narcolepsy it seems most likely that receipt of this vaccine in December 2009 caused Miss Clack's narcolepsy," said Mr Cooper. 

He added that narcolepsy triggers depression, though he noted the case of Miss Clack was "complex and very rare". 

Miss Clack's family is represented by Peter Todd and Freya Colvin, of law firm Hodge Jones & Allen. 

A statement issued on behalf of the family said: "Katie was an energetic young woman who had just discovered her passion working with children. 

"Narcolepsy turned her life into a terrible daily struggle and drastically reduced her quality of life. 

"We cannot believe she would have decided to take her own life had the balance of her mind not been disturbed." 

Miss Colvin added: "The Clack family has waited a long time for this inquest. 

"It is important that the coroner has recognised the causal link between the vaccine and narcolepsy and the devastating impact this had on Katie's short life." 

Earlier this year a boy who developed the sleeping disorder caused by the swine flu vaccine was awarded £120,000 in damages. 

Josh Hadfield, 10, from Frome in Somerset, developed narcolepsy after receiving the Pandemrix vaccine six years ago. 

In 2013, lawyers launched a class action on behalf of 38 Britons – including 19 children – who developed narcolepsy after having the vaccine. 

Scientists from the former Health Protection Agency (HPA) said there was evidence of a link between the Pandemrix jab – manufactured by GlaxoSmithKline(GSK) - and narcolepsy in children. 

HPA figures suggested one in 55,000 children vaccinated - about 20 in the UK – are thought to have developed narcolepsy.