Factors associated with incomplete or delayed vaccination across countries: A systematic review

Despite the significant decline in the incidence of vaccine-preventable diseases as a result of increased vaccination coverage worldwide, there are many children with delayed vaccination and a marked heterogeneity in vaccination coverage.

The aim of this study was to review factors that influence the adherence to childhood immunization schedule in different countries, especially related to socioeconomic conditions and health care system characteristics.

Pubmed and Web of Science databases were searched systematically for observational studies published in peer-reviewed journals in English, Spanish and Portuguese languages from January 1992 to June 2014. We included original articles that assessed vaccination schedule with at least three diphtheria-tetanus-pertussis, three polio and one measles vaccines in children aged 0-24 months.

491 articles were identified and 23 met the inclusion criteria and were reviewed. The most cited factors reported by countries with distinct characteristics were higher birth order (9 articles, 39.1%), and low maternal education/socioeconomic status (7 articles each one, 30.4%). Irregular monitoring by the health care services was reported by countries with "mainly private" health care system. Out-of-hospital birth, no reminder(s) about the next follow-up visit, and mother working outside the home were cited by countries with low/medium Human Development Index (HDI). Ethnicity, use of private health care services, and no health insurance were cited by countries with very high HDI. The role of migration on vaccination coverage was reported by three studies conducted in countries with distinct characteristics.

The factors are complex and driven by context. Overall, strengthening the contacts and relationships between the health care services and mothers with several children and families with low educational level/low socioeconomic status appear to be an important action to improve vaccination coverage.