How Well Does Vaccine Literacy Predict Intention to Vaccinate and Vaccination Status? A Systematic Review and Meta-analysis

"The results may contribute to a better understanding of VL as a potential predictor of vaccination adherence and may point toward more targeted strategies for implementing vaccination adherence."

Researchers have investigated various factors to assess their influence on vaccination behaviour, including vaccine literacy (VL). Vaccine literacy, a form of health literacy (HL), has been defined as "individuals' knowledge, motivation, and skills to find, understand, and evaluate immunization-related information in order to make adequate immunization decisions" (Health Literacy Survey Consortium). As with HL, VL is affected by socio-economic status and level of education, among other factors. This systematic review and meta-analysis quantified the association of VL and vaccination intention and status.

The researchers searched PubMed, Scopus, and Web of Science for any study, published until December 28 2022, that investigated the associations of interest. For each outcome, the 18 articles that met inclusion criteria were grouped according to the vaccine administrated, and results were narratively synthesised. As for the VL domains, since they investigate different capabilities of individuals, the researchers considered separately: overall VL, functional VL, interactive VL, critical VL, and interactive/critical VL. These different domains reflect distinct abilities: Functional questions deal with language skills, while the interactive and critical tasks involve problem-solving and decision-making processes. Inverse-variance random-effect models were used to compare standardised mean values in VL domain(s) between two groups: individuals willing vs. unwilling to get vaccinated, and individuals vaccinated vs. unvaccinated.

The meta-analysis found a statistically significant association between the intention to be vaccinated and overall VL score (N = 3, standardised mean difference (SMD) = 0.51, 95% confidence interval (CI): 0.20 to 0.82, I2 = 89.0%), functional VL (N = 7, SMD = 0.34, 95% CI: 0.10–0.58, I2 = 94.0%), interactive VL (N = 3, SMD = 0.42, 95% CI: 0.17 to 0.68, I2 = 90.0%), critical VL (N = 3, SMD = 0.50, 95% CI: 0.38 to 0.61, I2 = 54.0%), and interactive/critical VL (N = 5, SMD = 0.42; 95% CI: 0.21 to 0.62, I2 = 84.0%).

However, the review found that the association of VL with vaccination status is attenuated and barely significant, suggesting that other factors influence the actual vaccination uptake. Specifically, there was a nonstatistically significant association between being vaccinated and overall VL score (N = 2, SMD = 0.17, 95% CI: -0.01 to 0.35, I2 = 0.0%) or in relation to functional VL score (N = 3, SMD = 0.23, 95% CI: −0.11 to 0.57, I2 = 82.0%), though a significant association for interactive/critical VL score (N = 4, SMD = 0.22, 95% CI: 0.04 to 0.39, I2 = 52.0%).

Based on the findings, the researchers suggest that more studies are needed to help establish the influence of VL on the actual uptake of vaccination, possibly using observational designs other than cross-sectional studies. In addition, these studies should also better specify the definition of the outcome, which in some cases was unclear, and they should confirm the vaccination status of their participants, allowing a more accurate measurement of the outcome.

Notably, the researchers found a stronger association between VL and intention to be vaccinated among general population, even though most of the studies recruited individuals using the internet, a factor that may challenge the representativeness of these samples. On the other hand, the few studies that focused on healthcare workers or nursing students found mixed evidence of an association between VL and both outcomes (i.e., vaccination intention and status), suggesting that this category should be further investigated, especially considering the implications that this finding may have for both the subjects themselves and the patients they care for.

In short, given the scarce evidence available, the heterogeneity in the methods applied, and some limitations of the studies included, further research should be conducted to confirm the role of VL in the vaccination decision-making process.