The family of a teen who developed narcolepsy after receiving the Pandemrix swine flu vaccination is taking legal action.

The UK government stopped issuing the vaccine – which is made by medicine giants GlaxoSmithKline – to anyone under 20 from 2011, after the Health Protection Agency linked it to the neurological disorder. At least 1000 vaccine-linked cases have been identified across the world.

Experts believe an ingredient added to make the vaccine more potent may be to blame as a similar vaccine in the US with no added chemicals did not produce any cases of narcolepsy.