Table 1.

Summary of each included study.

Author, Year	Study Design	Scope of Study	Study Sample	HL Areas Investigated, HL Measurement Tools	Vaccinations Investigated	HL and Vaccination: Results
Aharon et al.,201725	Cross-sectional study	To investigate the relationship between the HL of parents and their compliance with the recommended child vaccinations	731 parents of children aged between three and four years	Functional, communicative, and critical HL were evaluated using the Vaccine Health Literacy Scale, a questionnaire with 13 items adapted from the HL Questionnaire developed by Ishikawa, Takeuchi, and Yano	Hepatitis B, diphtheria–tetanus–pertussis, mumps, measles, and rubella These are routinely administered during the first year of life and represent the core vaccination protocol	Communicative HL has a significant negative direct association with vaccination compliance; parents with highly functional, communicative, and critical HL are more at risk of not vaccinating their children (through significant negative indirect association)
			Two groups identified:
			Children who did not complete at least one of the three childhood vaccinations
			Control group of children who completed the three vaccinations (Country: Israel)
Bennett et al.,200920	Cross-sectional study	To assess whether HL contributes to racial/ethnic and education-related disparities in preventive health behaviours (including influenza vaccinations) among older adults	2,668 adults aged 65 years and above (Country: USA)	Functional HL was evaluated using the HL scale of the NAAL, which comprised health-related tasks (12 prose items, 12 documents, and four quantitative items)	Influenza vaccination	Increased HL is associated with the likelihood that an older adult would have received the influenza vaccination
						Health-related print literacy significantly mediated the racial/ethnic disparity in self-rated health status and the receiving of the influenza vaccination
Johri et al., 201526	Cross-sectional study	To investigate whether maternal HL is associated with children receiving vaccines in two Indian communities	Mothers of children aged 12–23 months, living in urban or rural sites (1,170 women from 60 villages and 670 women from nine slums) (Country: India)	Functional HL was evaluated using an HL tool developed from Indian child health promotion materials, consisting of questions related to three images	Diphtheria–tetanus–pertussis vaccination (three doses) (DTP3)	Maternal HL is independently associated with child vaccination; there is a positive association between maternal HL and DTP3
Lee et al., 201527	Cross-sectional study (secondary data analysis from two surveys)	To investigate predictors of the HPV vaccination in young Asian, American, and Pacific Islander (AAPI) and non-Latina white (NLW) women	This study was conducted at a public university in the Midwest (USA) and involved 2,270 women of college-going age (18–25 years): 341 AAPI and 1,929 NLW (Country: USA)	HPV vaccine literacy was ascertained based on the number of correct answers to a questionnaire with five items; the questions were adopted from the vaccination guidelines created by the National Cancer Institute	HPV vaccination	In both groups of undergraduate women, HPV vaccine literacy was a significant predictor related to completion of the HPV vaccination
Moran et al.,201721	Cross-sectional study	To investigate the predictors of influenza vaccination among Hispanic female subgroups in the USA	1,565 Hispanic females aged 21–50 years (Country: USA)	Functional HL was investigated using Chew's SBSQ	Influenza vaccination	Vaccine safety confidence varied according to the HL. Those with higher HL were more confident about vaccine safety
						The frequency of influenza vaccination did not vary significantly in accordance with HL. But confidence in vaccine safety was associated with a greater likelihood of regular influenza vaccination
Pati et al., 201122	Longitudinal prospective cohort study	To investigate the association between maternal HL and early immunization status	506 mother–infant dyads (Country: USA)	Functional HL was investigated S-TOFHLA	Hepatitis B, polio, Haemophilus influenzae Type B, pneumococcal, diphtheria–tetanus–pertussis vaccinations	Maternal HL was not significantly associated with immunization status at either three or seven months
Smith et al., 201523	Cross-sectional study (single-mode mail survey)	To investigate the association between HL and HPV awareness and knowledge	3,165 adult respondents to the survey (Country: USA)	Functional HL was evaluated using NVS	HPV vaccination	Significant associations between HL and awareness of HPV, awareness of the HPV vaccine, and correct knowledge that HPV can cause cervical cancer
Veldwijk et al.,201524	Cross-sectional study	To evaluate if HL is associated with parental preferences	467 Dutch parents of newborns aged six weeks	Functional HL was investigated using Chew's SBSQ (a subjective measure of HL containing three items)	Rotavirus vaccination	HL is associated with parental preferences for rotavirus vaccination
		concerning childhood vaccinations				Respondents with lower HL considered the duration of protection to be more important, and vaccine effectiveness and frequency of severe side effects to be less important, as compared to respondents with higher HL and education
White et al., 200812	Cross-sectional study	To identify the relationship between HL and self-reported preventive health practices (including influenza and pneumococcal vaccination) of adults in the USA	18,000 representative adults (aged 16 years and above) (Country: USA)	Functional HL was evaluated using the NAAL health literacy scale (with 28 health-related items)	Influenza and pneumococcal vaccination (the latter only for adults aged 65 years or above)	For adults aged 65 years and above, a significant positive association was found between HL and influenza vaccination; meanwhile, HL was not positively associated with pneumococcal vaccination
						For adults younger than 40 years, a negative relationship was found between HL and the influenza vaccination