1. Vaccination against the ten selected pathogens is projected to avert 69 million deaths between 2000 and 2030.
2. Increases in vaccine coverage and introduction of additional vaccines may result in a 72% reduction in lifetime mortality in the 2019 birth cohort.
Evidence Rating Level: 2 (Good)
Study Rundown: Vaccines are among the most cost-effective health interventions as they provide both direct and indirect protection to individuals. Due to the inconsistency of disease surveillance systems, directly measuring the impact of vaccination programmes in low- and middle-income countries (LMICs) is not always possible. Mathematical models can be used, instead, to extrapolate from available data to generate estimates and projections of future vaccine coverage. This study aimed to quantify the impact of vaccination programmes by estimating the deaths and disability-adjusted life-years (DALYs) averted by vaccination against ten pathogens in 98 LMICs between 2000 and 2030. 16 independent modelling groups were used to provide pathogen-specific vaccine impact estimates for hepatitis B virus, Haemophilus influenzae type B, HPV, Japanese encephalitis, measles, Neisseria meningitidis serogroup A, Streptococcus pneumoniae, rotavirus, rubella virus, and yellow fever virus. According to modeling results, vaccination in 98 LMICs greatly reduced overall mortality rates between 2000 and 2020 and may prevent approximately 32 million deaths between 2020 and 2030. Vaccines against measles, H influenzae type B, and S. pneumoniae had the largest relative impact on mortality of children younger than 5 years while those against HPV, hepatitis B virus, and yellow fever had the largest impact per person vaccinated by year of birth. This study was limited by the assumption that all LMICs assessed will continue to have equal or increased vaccination coverage in the years to come. Perhaps, a model that takes into account the possibility of a shortage in vaccination supply would help to increase its validity.
Relevant Reading: Mapping routine measles vaccination in low- and middle-income countries
In-depth [retrospective cohort]: Two mathematical models were used for each pathogen other than hepatitis B virus, which had three, and yellow fever, which had one. Each model represented the impact of vaccine coverage, assessed by comparing the counterfactual scenario (no vaccination) with the reported and projected vaccination scenarios. Standardized demographic data (live births per year and death rates) was used for all countries. While the past coverage in all countries for 1980-2016 was obtained from WHO-UNICEF Estimates of National Immunization Coverage, future coverage estimates from 2017 to 2030 were based on Gavi’s (the Vaccine Alliance’s) operational forecast as of October 2017.
Between 2000 and 2019, the average number of vaccines received per child increased across the majority of the 98 LMICs. According to the model, 69 million (95% credible intervals [CrI] 52-88) deaths were estimated to be averted between 2000 and 2030. Of these, 37 million (95% CrI 30-48) were averted between 2000 and 2019. During this time, vaccination in the 98 LMICs reduced overall mortality by 45% (95% CrI 36-58) and mortality among children younger than 5 years by 57% (95% CrI 52-66). It is predicted that vaccination will prevent 72% (95% CrI 59-81) of the mortality associated with these ten pathogens in the 2019 birth cohort across the countries considered. The impact of vaccination over the full lifetimes of the 2000-2030 birth cohorts was equally substantial with a total of 120 million (95% CrI 93-150) estimated deaths averted, of which 65 million (95% CrI 48-83) are in children younger than 5 years. Of the ten pathogens, vaccination against measles had the largest impact between 2000-2030, with 56 million (95% CrI 39-74) deaths averted. In contrast, yellow fever and HPV vaccination had the largest relative impact between 2000-2019, with estimates for both vaccines over 16 (95% CrI 5-32) deaths averted per 1000 persons vaccinated. Overall, this study emphasizes the need to increase vaccine coverage and maintain high coverage levels in all countries to mitigate vaccine-related morbidity and mortality.
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