bb Hernan 2004.

Methods	Case‐control study based on the General Practice Research Database (GPRD)
Participants	Cases (n = 163): patients with confirmed diagnosis of multiple sclerosis between 1 January 1993 and 31 December 2000. Controls (n = 1604): subjects from the GPRD matched to the cases for age, sex, practice, date of joining the practice.
Interventions	Exposure to vaccinations (also influenza) as shown from medical records
Outcomes	Association between exposure to influenza vaccine and onset of multiple sclerosis
Notes	Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
CC ‐ case selection All outcomes	Low risk	Nested case‐control from GPRD registry
CC ‐ control selection All outcomes	Low risk	GPRD registry
CC ‐ comparability All outcomes	Low risk	Matched
CC ‐ exposure All outcomes	Low risk	Registry
Summary assessment	Low risk	Low