“We will have to think again,” said Maria Szirmai of the Swedish Medical Products Agency to newspaper Göteborgsposten (GP).
Over 220 Swedes, most of them children, developed narcolepsy as a side effect from the Swine flu vaccine Pandemrix, according to the reports filed with insurance company Läkemedelsförsäkringen.
All these had received the vaccine from some 12 of the 35 batches of vaccine delivered to Sweden.
From 23 of the 35 shipments there is no recorded case of anyone developing the condition, according to the study, which was carried out by the Swedish Narcolepsy Association (Narkolepsiföreningen).
The association traced the vaccine through the batch number on the side of the boxes.
Their findings will now be investigated by the agency, which has previously denied any connection between different vaccine shipments and the onset of narcolepsy.
In some parts of Sweden, namely in counties Skåne, Västra Götaland, Dalarna and Uppland, there are more children affected by narcolepsy than anywhere else in the country, which has so far flummoxed researchers.
Over half a million Swedes were vaccinated against swine flu with Pandemrix between autumn 2009 and spring 2010.