bb Mutsch 2004.

Methods	1 case‐control study and case series based in the German‐speaking regions of Switzerland, which assessed the association between an intranasal inactivated virosomal influenza vaccine and Bell's palsy
Participants	250 cases that could be evaluated (from an original 773 cases identified) were matched to 722 controls for age and date of clinic visit. All participants were around age 50.
Interventions	Immunisation with influenza vaccine took place within 91 days before disease onset.
Outcomes	Bells' palsy
Notes	The study reports a massive increase in risk (adjusted OR 84, 95% CI 20.1 to 351.9) within 1 to 91 days since vaccination. Despite the many limitations of the study (case attrition: 187 cases could not be identified; ascertainment bias: physicians picked controls for their own cases; confounding by indication: different vaccine exposure rate between controls and the reference population), it is unlikely that such a large OR could have been significantly affected by systematic error. The authors called for larger pre‐licence safety trials, given the rarity of Bell's palsy. On the basis of this study the vaccine was withdrawn commercially. Rare events (safety) Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
CC ‐ case selection All outcomes	Low risk	"All 4891 primary care physicians, ear, nose, and throat specialists, and neurologists in the study area were invited twice to report cases of Bell’s palsy first diagnosed between October 1, 2000, and April 30, 2001."
CC ‐ control selection All outcomes	Low risk	Subsequently, the physicians who had reported cases of Bell’s palsy were asked to document the date of the visit and information pertinent to the study’s inclusion and exclusion criteria and to select from among their patients without Bell’s palsy, 3 controls sequentially from their registration log. Trained study monitors contacted the physicians and reviewed the selection forms regularly to ensure consistency in the selection of controls. At this point, participating physicians had not been made aware of the exposure to be investigated (influenza vaccination).
CC ‐ comparability All outcomes	Unclear risk	The controls were matched with the case patients according to age (within 5 years), date of the clinic visit (within 4 days), and physician.
CC ‐ exposure All outcomes	Low risk	"Physicians were asked to document the dates of administration and the brand name and type of influenza vaccine (parenteral or intranasal) used during the study period. Other vaccine exposures during the study period and the preceding 2 months were also documented. Since in all 43 sentinel cases reported in the study area the onset of Bell’s palsy occurred within 91 days after intranasal vaccination, we defined the period of 1 to 91 days as the postexposure risk period."
Summary assessment	Unclear risk	Unclear