eTable. Risk of bias in the studies identified in the systematic review and included in the meta-analysis.

Study	Confounding factors	Selection bias	Documentation of the intervention	Variant intervention	Missing data	Documentation of the outcome	Publication bias	Overall risk of bias
Yung et al. (26)	++	++	++	++	++	++	++	++
Escolano et al. (27)	++	+	++	++	++	?	++	++
Carlin et al. (34)	++	++	++	++	++	++	++	++
Pérez-Vilar et al. (28)	+ *	++	++	++	++	++	++	+
Yih et al. (29)	+ *	++	++	++	++	++	++	+
Velázquez et al. (30)	++	++	++	++	++	++	++	++
Patel et al. (18)	++	++	++	++	++	++	++	++
Haber et al. (31)	+ *	++	++	++	++	++	++	+
Haber et al. (32)	+ *	++	++	++	++	++	++	+
Stowe et al. (33)	++	++	++	++	++	++	++	++

++ low risk; + moderate risk; ? no information;

* only vaccinated infants. not adjusted