Timeliness of routine childhood vaccination in 103 low-and middle-income countries, 1978-2021: A scoping review to map measurement and methodological gaps

Abstract

Empiric studies exploring the timeliness of routine vaccination in low-and middle-income countries (LMICs) have gained momentum in the last decade. Nevertheless, there is emerging evidence suggesting that these studies have key measurement and methodological gaps that limit their comparability and utility. Hence, there is a need to identify, and document these gaps which could inform the design, conduct, and reporting of future research on the timeliness of vaccination. We synthesised the literature to determine the methodological and measurement gaps in the assessment of vaccination timeliness in LMICs. We searched five electronic databases for peer-reviewed articles in English and French that evaluated vaccination timeliness in LMICs, and were published between 01 January 1978, and 01 July 2021. Two reviewers independently screened titles and abstracts and reviewed full texts of relevant articles, following the guidance framework for scoping reviews by the Joanna Briggs Institute. From the 4263 titles identified, we included 224 articles from 103 countries. China (40), India (27), and Kenya (23) had the highest number of publications respectively. Of the three domains of timeliness, the most studied domain was 'delayed vaccination' [99.5% (223/224)], followed by 'early vaccination' [21.9% (49/224)], and 'untimely interval vaccination' [9% (20/224)]. Definitions for early (seven different definitions), untimely interval (four different definitions), and delayed vaccination (19 different definitions) varied across the studies. Most studies [72.3% (166/224)] operationalised vaccination timeliness as a categorical variable, compared to only 9.8% (22/224) of studies that operationalised timeliness as continuous variables. A large proportion of studies [47.8% (107/224)] excluded the data of children with no written vaccination records irrespective of caregivers' recall of their vaccination status. Our findings show that studies on vaccination timeliness in LMICs has measurement and methodological gaps. We recommend the development and implement of guidelines for measuring and reporting vaccination timeliness to bridge these gaps.

Fig 1. Flowchart showing study identification, screening, and selection process.

Fig 2

(a) How the literature on the timeliness of routine childhood vaccination has evolved, 1978–2021 Number of studies published per year (b) number of studies published per WHO region (c) antigens studied in the published literature.

Fig 3. Map of the world showing low-and middle-income countries where studies on the timeliness of routine childhood vaccination has been conducted, 1978–2021.

This map was produced by the authors with administrative boundaries data from geoBoundaries [22].

Fig 4

How the timeliness of routine childhood vaccination was defined and measured in the literature, 1978–2021 (a) domains of timeliness explored and how timeliness was operationalised (b) how untimely interval vaccination was defined (c) how early vaccination was defined (d) how delayed birth-dose hepatitis-B vaccine (HBV-BD) was defined. Note, in Fig 4D, the definition timelines are relative to the day of birth.

Fig 5. Determinants of the timeliness of routine childhood vaccination studied in low-and middle-income countries, 1978–2021.

Note: Delay 1, 2, and 3 are based on the 3-delay conceptual framework developed by Thaddeus and Maine [21].