Table 4.

Quality assessment for case–control studies

			Selection				Comparability	Exposure			Number of star
Vaccine	Study	Year of publication	Is the case definition adequate?	Representativeness of the cases	Selection of controls	Definition of controls	Comparability of cases and controls on the basis of the design or analysis	Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-response rate
Influenza	Chang et al	2016	a)*	a)*	b)	a)*	*	a)*	a)*	a)*	7
Influenza	Chiang et al	2017	a)*	a)*	a)*	a)*	*	a)*	a)*	c)	7
Influenza	Grau et al	2005	a)*	a)*	a)*	a)*	*	b)*	a)*	c)	7
Influenza	Heffelfinger et al	2006	a)*	a)*	b)	a)*	*	d)	a)*	c)	5
Influenza	Lavallée et al	2002	a)*	a)*	b)	a)*	**	d)	b)	c)	5
Influenza	Liu et al	2017	a)*	a)*	a)*	a)*	**	a)*	a)*	a)*	9
Influenza	Lin et al	2014	a)*	a)*	b)	a)*	**	a)*	a)*	a)*	8
Influenza	Seo et al	2014	c)	a)*	b)	b)	**	d)	b)	c)	3
Influenza	Siriwardena et al	2010	a)*	a)*	b)	b)	*	a)*	a)*	a)*	6
Influenza	Piñol-Ripoll et al	2008	b)	a)*	b)	a)*	**	a)*	a)*	a)*	7
Influenza	Meyers et al	2004	a)*	a)*	b)	a)*	**	d)	a)*	c)	6
Influenza	Abajo et al	2021	a)*	a)*	b)	a)*	**	a)*	a)*	a)*	8

*a star attests to the quality of the study for each criterion