A widely used swine flu vaccine has been placed under investigation after reports it causes cases of the rare sleeping disorder narcolepsy.
Pandemrix, which was the main drug administered in the UK during the 2009 flu pandemic, is being investigated by the European Medicines Agency over a possible link with the condition, which causes people to unexpectedly fall asleep.
At least 30.8 million Europeans received the GlaxoSmithKline vaccine, with most UK recipients belonging to high-risk groups including children and people with asthma, diabetes and heart disease.
In a statement, the European Agency said: "The Agency's Committee for Medicinal Products for Human Use (CHMP) will look carefully at all of the available data to determine whether there is evidence for a causal association.
Narcolepsy cases were mainly reported in Finland and Sweden, but doctors and parents across Europe have been urged to monitor their children as research shows they are more likely to develop high temperature fever after the second dose of the vaccine.
Other side-effects which are more prominent after the second shot are soreness at the injection site, loss of appetite, drowsiness and irritability.