In Sweden, H1N1 vaccinations were initially (from the start of the campaign selleck chemical Bosutinib in mid-October 2009 and during the subsequent one and half months) targeted at healthcare workers and groups considered to be at high risk of complications from influenza��that is, children with multifunctional disorders; pregnant women; patients with chronic heart or lung disease, diabetes mellitus, chronic liver failure, chronic renal failure, or immunosuppression; people with extreme obesity (body mass index >40); and patients with neuromuscular disease affecting breathing capacity. Data on diagnoses from primary care and hospitals showed that an estimated 10% of the population had a chronic condition putting them at risk.22 We considered people who received at least one dose of vaccine.
A potential effect of a second dose was not evaluated. Outcomes and definitions For the purposes of this study we defined the pandemic period as starting on 1 October 2009. The vaccination campaign with Pandemrix started in mid-October. We linked individualised data on vaccination to data on utilisation of inpatient and specialist healthcare in the common healthcare registers for Stockholm County Council (the GVR) from 1 January 1998 to 31 August 2010. This database contains information on all admissions to hospital and visits to specialist care in the county, such as dates, diagnoses (international classification of diseases), responsible medical departments, and length of hospital stay. Data in the healthcare database are continually transferred to the healthcare administration database, where a patient��s identity number is replaced by a code number.
23 We used the same key for coding for the Vaccinera database to be able to link the two systems on an individual basis without revealing the patient��s identity. Neurological and autoimmune diagnoses We selected Brefeldin_A neurological and autoimmune diagnoses for follow-up in line with the European Medicines Agency strategy for monitoring the safety of pandemic vaccines,21 defined according to ICD-10 (international classification of diseases, 10th revision) codes for hospital admissions and visits to specialist care (see web extra appendix). Neurological outcomes of special interest included Guillain-Barr�� syndrome, Bell��s palsy, multiple sclerosis, polyneuropathy, anaesthesia or hypoaesthesia, paraesthesia, narcolepsy, and autoimmune conditions such as rheumatoid arthritis, inflammatory bowel disease (ulcerative colitis, Crohn��s disease), and type 1 diabetes. Entering diagnoses into the county healthcare database is part of the doctor��s routine diagnostic work and therefore depends on patients seeking healthcare. We did not actively search for adverse events during the study period.