**1. Introduction**

The number of children not receiving a single dose of routine vaccine (defined as the first dose of diphtheria, tetanus, and pertussis (DTP1) non-receipt), also referred as "zero-dose children", increased by 5 million in 2021 compared with 2019, going from 13 to 18 million. More than 60% of these children live in extremely poor conditions facing a lack of access to reproductive health services, water, and sanitation [1]. Health equity has been increasingly incorporated into economic evaluations of vaccines to foster equitable access. The Immunization Agenda 2030 prioritizes populations that are not being reached through current immunization efforts—particularly the most marginalized communities, those living in fragile and conflict-affected settings, mobile populations, and those moving across borders [2]. Robust and standardized methods are needed to evaluate the health equity impact of vaccination programs to ensure monitoring and effective addressing of inequities.

The Immunization Agenda 2030, through its Strategic Priority 3, addresses equity by defining key areas of focus and objectives to reach the goal of protecting everyone with

**Citation:** Patikorn, C.; Cho, J.-Y.; Lambach, P.; Hutubessy, R.; Chaiyakunapruk, N. Equity-Informative Economic Evaluations of Vaccines: A Systematic Literature Review. *Vaccines* **2023**, *11*, 622. https:// doi.org/10.3390/vaccines11030622

Academic Editor: Davide Gori

Received: 10 February 2023 Revised: 1 March 2023 Accepted: 2 March 2023 Published: 9 March 2023

**Copyright:** © 2023 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons. org/licenses/by/4.0/).

full immunization, regardless of location, age, socioeconomic status, or gender-related barriers [2]. The World Health Organization's "Guide for Standardization of Economic Evaluations of Immunization Programmes" also recommends that the health equity impact be included if it is considered an important factor for decision-making [3]. These recommendations emphasized the need to explore and summarize how health equity was incorporated and evaluated in the existing literature on economic evaluations of vaccines.

Health technology assessment has been employed in many countries to inform healthcare decision-making [4]. This is especially relevant to countries aiming to provide accessible, affordable, equitable, and high-quality healthcare services to their populations while ensuring the sustainability of health systems in place. Equity-informative assessments can provide data on the health equity impact of health technologies and public health policies and the inherent tradeoff between total coverage and equitable coverage. Based on these data, decision-makers can better balance the efficient use of limited budgets and foster equitable access to healthcare. Health equity impact analysis has been increasingly incorporated into the economic evaluations of health technologies and public health policies, including vaccines [5–13]. Health equity impact analysis is conducted to estimate the distribution of impact of alternative policy options, broken down by one or more variables of concern to policymakers from an equity perspective [14]. Nevertheless, varying methods to evaluate the health equity impact can affect the application of findings to inform policy decision-making.

Several systematic reviews summarize equity-informative economic evaluations in terms of methodological aspects and the application of the methods in general [5,15–19]. However, no systematic review comprehensively describes how health equity is incorporated into the economic evaluations of vaccines. In addition, economic evaluations of vaccines differ from other health technologies given the unique characteristics of vaccines, such as program deployment costs, vaccination coverage, and herd protection [3]. Therefore, we conducted a systematic literature review to identify economic evaluations of the health equity impact of vaccines and immunization programs, focusing on the methods and applications.

#### **2. Materials and Methods**

The protocol of this review was registered with PROSPERO (CRD42022382729). We reported this review following the 2020 Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) [20]. The PRISMA checklist table of this review is provided in Table S1 in the Supplementary Materials.
