Health literacy and vaccination: A systematic review

Figures & data

Figure 1. Flow diagram of study selection.

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.,2017^25	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.,2009^20	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., 2015^26	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., 2015^27	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.,2017^21	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., 2011^22	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., 2015^23	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.,2015^24	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., 2008^12	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

Table 2. Results of methodological quality assessment of all included studies.

ITEM (description)^19	Aharon, 2017^25	Bennett, 2009^20	Johri, 2015^26	Lee, 2015^27	Moran, 2017^21	Pati, 2011^22	Smith, 2015^23	Veldwijk, 2015^24	White, 2008^12	%
1. Are the objectives or hypotheses of the study stated? (Self-explanatory)	1	1	1	1	1	1	1	1	1	100.0
2. Is the target population defined? (The group of persons toward whom inferences are directed. Sometimes the population from which a study group is drawn)	1	1	1	1	1	1	0	1	1	88.9
3. Is the sampling frame defined? (The list of units from which the study population will be drawn)	0	1	1	1	1	1	0	1	1	77.8
4. Is the study population defined? (The group selected for investigation)	1	1	1	1	1	1	0	1	1	88.9
5. Are the study settings (venues) and/or geographic locations stated? (Comment required about location of research. Could include name of center, town, or district)	1	1	1	1	1	1	0	1	1	88.9
6. Are the dates during which the study was conducted stated or implicit? (Self-explanatory)	1	1	1	1	1	1	0	0	1	77.8
7. Are the eligibility criteria stated? (The words “eligibility criteria” or equivalent are needed, unless the entire population is the study population)	1	1	1	1	1	1	0	1	1	88.9
8. Are the issues of ‘selection in’ to the study mentioned? (Any aspect of recruitment or setting that results in the selective choice of participants)	0	0	0	0	0	0	0	1	0	11.1
9. Is the number of participants justified? (Justification of number of subjects needed to detect anticipated effects. Evidence that power calculations were considered and/or conducted.)	0	1	0	0	0	1	0	0	1	33.3
10. Are numbers of participants meeting and not meeting the eligibility criteria stated? (Quantitative statement of numbers)	0	0	0	0	1	1	0	0	0	22.2
11. For those not eligible, are the reasons why stated? (Broad mention of the major reasons)	0	0	0	0	0	1	0	0	0	11.1
12. Is the number of people who did/did not consent to participate stated? (Quantitative statement of numbers)	0	0	0	0	0	1	0	1	0	22.2
13. Are the reasons people refused to consent stated? (Broad mention of the major reasons)	0	0	0	0	0	0	0	0	0	0
14. Were consenters compared with non-consenters? (Quantitative comparison of the different groups)	0	0	0	0	0	1	0	0	0	11.1
15. Was the number of participants at the beginning of the study stated? (Total number of participants -after screening for eligibility and consent- included in the first stage of data collection)	1	1	1	1	1	1	0	1	0	77.8
16. Were methods of data collection stated? (Descriptions of tools)	1	1	1	1	1	1	0	1	1	88.9
17. Was the reliability (repeatability) of measurement methods mentioned? (Evidence of reproducibility of the tools used)	0	1	0	0	0	1	0	1	1	44.4
18. Was the validity (against a ‘gold standard’) of methods of measurement mentioned? (Evidence that the validity was examined against, or discussed in relation to, a gold standard)	0	1	0	0	0	1	0	1	1	44.4
19. Were any confounders mentioned? (Confounders were defined as a variable that can cause or prevent the outcome of interest, is not an intermediate variable, and is associated with the factors under investigation)	1	1	1	1	1	1	0	1	1	88.9
20. Was the number of participants at each stage/wave specified? (Quantitative statement of numbers at each follow-up point)	NA	NA	NA	NA	NA	1	NA	NA	NA	100.0
21. Were reasons for lack of follow-up quantified?^* (Broad mention and quantification of the major reasons)	NA	NA	NA	NA	NA	0	NA	NA	NA	0
22. Was the number of missing data items at each wave mentioned?^* (Differences in numbers of data points -indicating missing data items- explained)	NA	NA	NA	NA	NA	1	NA	NA	NA	100.0
23. Were the types of analyses conducted stated? (Specific statistical methods mentioned by name)	1	1	1	1	1	1	1	1	1	100.0
24. Were ‘longitudinal’ analysis methods stated?^* (Longitudinal analyses were defined as those assessing change in outcome over two or more time points and that take into account the fact that the observations are likely to be correlated)	NA	NA	NA	NA	NA	1	NA	NA	NA	100.0
25. Were absolute effect sizes reported? (Absolute effect was defined as the outcome of an exposure expressed, for example, as the difference between rates, proportions, or means, as opposed to the ratios of these measures)	0	0	0	0	0	0	0	0	0	0
26. Were relative effect sizes reported? (Relative effects were defined as a ratio of rates, proportions, or other measures of an effect)	1	1	1	1	1	1	1	1	1	100.0
27. Was lack of follow-up taken into account in the analyses?^* (Specific mention of adjusting for, or stratifying by, loss to follow-up)	NA	NA	NA	NA	NA	0	NA	NA	NA	0
28. Were confounders accounted for in the analyses? (Specific mention of adjusting for, or stratifying by, confounders)	1	1	1	1	1	0	1	1	1	88.9
29. Were missing data accounted for in the analyses? (Specific mention of adjusting for, or stratifying by, or imputation of missing data items)	0	0	0	0	1	0	0	0	1	22.2
30. Was the impact of biases assessed qualitatively? (Specific mention of bias affecting results, but magnitude not quantified)	1	1	1	1	1	0	1	1	1	88.9
31. Was the impact of biases estimated quantitatively? (Specific mention of numerical magnitude of bias)	1	1	1	0	0	0	1	0	1	55.6
32. Did authors relate the results back to a target population? (A study is generalizable if it can produce unbiased inferences regarding a target population -beyond the subjects in the study)	1	1	1	0	0	1	1	1	1	77.8
33. Was there any other discussion of generalizability? (Discussion of generalizability beyond the target population)	1	0	1	1	1	1	0	1	1	77.8
Not applicable items	28	28	28	28	28	33	28	28	28
Total score, N (%)	16 (57.1)	19 (67.9)	17 (60.7)	15 (53.6)	17 (60.7)	24 (72.7)	7 (25.0)	19 (67.9)	20 (71.4)

* not for cross-sectional.

The term ‘critical HL’ refers to cognitive skills that can be applied to critically analyse information and use it to exert greater control over life events and situations.

The term ‘evaluation skills’ refers to the ability to filter, interpret, and evaluate information.

The term ‘interactive HL’ refers to more advanced cognitive and literacy skills that, together with social skills, can be used to actively participate in everyday situations, extract information and derive meaning from different forms of communication, and apply this to changing circumstances.⁵

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