cb Persson 2014.

Methods	Cohort study. Large prospective, register‐based cohort study assessing the possible association between monovalent, pandemic, H1N1 flu vaccine Pandemrix (GSK) and neurological or autoimmune disease, or both
Participants	The present study represents the extension of the cb Bardage 2011 study to the population of more Swedish regions, namely the healthcare regions of Skåne and Västra Götaland and the counties of Kalmar, Östergötland, Stockholm, Värmland, and Norrbotten. Included are 5,845,039 participants, corresponding to about 61% of the whole Swedish population in 2009.
Interventions	Exposure to Pandemrix between October 2009 and March 2010. Vaccinated participants were registered in vaccination centres and identified by means of a personal identification number (PIN, a 10‐digit number attributed to each newborn in Sweden) and linked to vaccination registries. Vaccination data are linked to the National Population Registry by use of the PIN: all individuals registered as vaccinated (n = 3,347,467) were exposed, whereas all remaining individuals were assumed not to be vaccinated (n = 2,497,572). Personal identification number was also linked to the following databases to obtain further information about participants: National Patient Register, Prescribed Drug Register, and Cancer Registry (National Board of Health and Welfare), to identify hospitalisations and non‐primary care outpatient visits to identify the outcomes under study; Medical Birth Register (National Board of Health and Welfare), to identify pregnancy status at vaccination; National Cause of Death Register (National Board of Health and Welfare), to define deaths during follow‐up.
Outcomes	Neurological and immuno‐related conditions Outcomes were selected under consideration of previous influenza safety issues, of the results of the previous study carried out in the Stockholm region only, and identified in the registers by using ICD‐10 codes and data about medical drug prescription. Due to the fact that several of the investigated outcomes could have a slow and insidious onset, “prodromal” conditions were identified by linking information present in the registers (date of visits, drug prescriptions, etc.) considering the 5 years preceding the study. Participants who had diagnosis before study start were excluded from risk assessment. As done in the previous study, risk estimates were stratified for “early” (vaccinated in the first 45 days from the beginning of the campaign) and “late” vaccination (vaccinated after at least 45 days from the beginning of the campaign), as medically “at risk” participants were considered to be priority group for influenza vaccination. Stratification considering time since vaccination (within/more than 1 year; within 6 weeks/more than 6 weeks) was also carried out. Association risk between vaccine exposure and outcomes was calculated by means of Cox regression using vaccination as time‐dependent variable (i.e. individuals contributed to the unexposed person‐time until vaccinated and to the exposed ones thereafter). Hazard risk estimates were adjusted for age (in 5‐year bands), gender and county, education and income, number of hospital admissions and ambulatory care visits, pregnancy status, and presence of diagnoses defined by ICD‐10 code.
Notes	Funding source: government Vaccination status could not be confirmed for 16% to 22% of the Kalmar, Värmland, and Norrbotten participants (corresponding to roughly 2.3% of the whole vaccinated cohort), because PIN was not available in the database. These participants were considered as unvaccinated.
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	Low risk	The exposed hemi‐cohort consists of all people who received the vaccine within 6 Swedish regions.
PCS/RCS ‐ selection non‐exposed cohort All outcomes	Low risk	Drawn from the same populations as the exposed cohort (all people who did not receive influenza vaccination)
PCS/RCS ‐ comparability All outcomes	Low risk	Age, gender and county, education and income, number of hospital admissions and ambulatory care visits, pregnancy status, and presence of diagnoses defined by ICD‐10 code.
PCS/RCS ‐ assessment of outcome All outcomes	Low risk	Medical records
Summary assessment	Low risk	Low risk of bias