The Swedish Medical Products Agency (Läkemedelsverket) ordered the massive study to determine if the vaccine had any connection to narcolepsy after dozens of reported cases of young people coming down with the affliction after receiving a swine flu jab.
The study, which took place between October 2009 and the December 2011, compared 3.3 million vaccinated Swedes with 2.5 million who were not vaccinated.
"We can see that over the whole study period we have 126 cases of those vaccinated getting narcolepsy," Ingemar Person, professor behind the study, said in a statement on Tuesday.
"There were 20 cases among those not vaccinated. We're talking about a threefold increase in risk."
The risk was found to be highest among the youngest people who took the vaccines. For those under the age of 21, the risk of contracting narcolepsy was three times higher for those who were vaccinated with Pandemrix, whereas those aged between 21 and 30 had double the risk.
Those vaccinated over the age of 40 had the same risk as those who didn't, according to the study.
Person added that it was "very difficult" to determine whether there was any connection with other sicknesses or diseases from taking the vaccine.