In 88 of the 93 cases, the agency has identified a direct correlation between the vaccine and the onset of narcolepsy, a sleep disorder causing extreme drowsiness and daytime sleep attacks.
According to the Swedish Association of Persons with Neurological Disabilities (Neurologiskt handikappades riksförbund - NHR), the agency is examining a further 135 cases involving children and will present its full findings later this summer.
NHR announced on Friday the launch of a 250,000 kronor ($40,000) research grant to facilitate studies of the relationship between Pandemrix, a drug manufactured by pharmaceutical giant GlaxoSmithKline, and narcolepsy.
“We are deeply concerned and have decided that things needs to happen, and quickly,” said NHR chair Kathleen Bengtsson-Hayward in a statement.
A study presented in March by the Medical Products Agency showed that children and adolescents under 20 vaccinated with Pandemrix could be up to four times as likely to develop narcolepsy as those not inoculated.
Since August 2010, at least 12 countries have reported cases of narcolepsy, particularly among children and adolescents, after receiving a swine flu, or H1N1, vaccine.
Figures from Sweden's National Board of Health and Welfare (Socialstyrelsen), show that 31 million people have been vaccinated with Pandemrix in Europe.
According to the WHO, the rates of narcolepsy reported in Sweden, Finland and Iceland were higher than those in other countries.