The High Court has begun hearing an action for damages by a student who claims she developed the sleep disorder narcolepsy after receiving a swine flu vaccine ten years ago.

Lawyers for Aoife Bennett from Naas, Co Kildare, told the High Court this was not an anti-vaccine case, but was about a once off badly managed vaccine, which had never been tested on children or teenagers.

In an opening speech expected to last three days in a ten-week case, Senior Counsel Dermot Gleeson said it was "unforgivable" that people were not told the vaccine had not been tested on children when it was administered by the Health Service Executive in 2009.

Mr Gleeson said there was "no message going out of this court room that people should not vaccinate their children."

It was not a case in support of the so-called anti-vaxx campaign, he said, adding that one of their expert witnesses will say that apart from clean water, vaccination is the single most important thing in a public health system.

However, he said "this is a good thing that went very badly off the rails. It was badly managed by Glaxo (the manufacturer) and badly managed by the State," he said.

In what is seen as a test case for up to 100 more, the court will be asked to determine if any or all of the defendants, including the vaccine maker and the State, are liable for damages.

The defendants include GlaxoSmithKline Biologicals, the Health Service Executive, the Minister for Health and the Health Products Regulatory Authority.

Ms Bennett was 16 when she was given the Pandemrix vaccine at school as part of a vaccination programme administered by the HSE.

The court heard she suffered life changing injuries as a result and was later diagnosed with narcolepsy - excessive daytime sleepiness and episodes of sudden weakness known as cataplexy.

Mr Gleeson said the rare autoimmune disease can be caused when those with a certain genetic variant receive a new adjuvant or booster contained in a vaccine.

He said the chemical used in the Pandemrix vaccine had never been tested on children and had very limited testing on adults.

Because narcolepsy was an auto immune disease, the vaccine affected children and teenagers in a different way because their immune systems were not fully developed, he said.

The narcoleptic effect of the vaccine was located in about 1,000 children across Europe and a public inquiry set up in Ireland concluded that the vaccine increased chances of becoming narcoleptic in those with a certain gene variant by 12 to 14%.

He said there were 75 to 100 children identified with the condition in Ireland, 350 in Sweden, up to 200 in Finland, 100 in France and in the UK and a handful in Denmark and the Netherlands.

There were virtually none in Germany because the authorities had advised against the vaccine.

The Government bought millions of doses of Pandemrix and another vaccine, Cevaplan, which is made by Baxter, during a threatened outbreak of swine flu in 2009.

Ms Bennett claims brochures issued by the HSE in September and November 2009 misled parents about the safety of the Pandemrix vaccine and about alleged risks associated with its use.

Mr Gleeson said by the time she was given the vaccine in December 2009 a lot more was known about the vaccine and the flu pandemic was all but over.

He said the HSE "knew the pandemic was almost dead, that the stuff was untested and in the figures being reported by Glaxo that adverse reactions and serious adverse reactions to Pandemrix were ten times the number being produced in Canada. While it was forgiveable to offer the vaccine it was unforgivable not to tell Aoife and her parents what they well knew about it at the time".

Mr Gleeson said there were seven key points that Ms Bennett and her family should have been made aware of.

These include the fact that the vaccine had not been tested on children, that the pandemic had not in fact materialised and was no worse than seasonal flu; that the State had indemnified GSK against any claims; that there was another vaccine Cevaplan which did not contain the adjuvant or booster and was strong enough by itself; that Pandemrix had been subject to a much less stringent testing regime than is normally used for vaccines and that the mass vaccination was stopped in Britain and Northern Ireland on 19 November that year because of the low risk.

Millions of doses of the vaccine had been dumped by the UK and Germany but Ireland continued to use it, he said, adding: "If Aoife Bennett had been in school in Newry rather than Naas she would not now be narcoleptic."

It is also claimed that the Irish Medicines Board - now the HPRA - wrote to the Department of Health in September 2009 noting there was no safety data available with the swine flu vaccines and no data was yet available from clinical trials which were then under way.

It is claimed that GSK had a liability to Ms Bennett under the Defective Products Act of 1991.

All claims are denied and the defendants will contend the Pandemrix vaccine was properly authorised by the European Commission for use in all EU member states and was required to address the swine flu pandemic.