eTable 2b. eTable 2 a continued.

Overall risk of bias assessment:			Low Risk	High Risk	Unclear Risk
Major domains	1. Recruitment procedure & follow-up (in cohort studies)
	2. Exposure definition and measurement
	3.1a Outcome “infection rate”. Source and validation
	3.1b Outcome “risk of infection”. Source and validation
	3.2 Outcome “Immunization coverage of the nursery-school teachers”. Source and validation
	3.3 Outcome “Immunity status of the nursery-school teachers. Source and validation
	4. Confounding and effect modification
	5. Analysis method: methods to reduce research specific bias
Minor domains	6. Chronology
	7. Funding
	8. Conflict of interest
General rule for rating:	Low risk of bias: low risk in all major domains High risk of bias: if not low risk	Overall assessment: