Increasing childhood immunizations in low- and middle-income counties (LMICs) saved an estimated 37 million lives from 2000-2019 — and the number of lives saved is projected to increase to 69 million by 2030, a modelling study found.
Over the past two decades, there has been a substantial expansion of childhood vaccination programs in LMICs; however, the incompleteness and inconsistent quality of death registration and disease surveillance systems in many LMICs makes it difficult to directly measure the impact of widespread vaccination programs on morbidity and mortality, Xiang Li, PhD, of the MRC Centre for Global Infectious Disease Analysis, Abdul Latif Jameel Institute for Disease and Emergency Analytics (J-IDEA), School of Public Health, Imperial College London, and colleagues from the Vaccine Impact Modelling Consortium (VIMC) explained in The Lancet.
The VIMC, which is comprised of 18 modelling groups administrated through Imperial College London, was founded in 2016 to model vaccination impact in 98 countries for 10 pathogens: hepatitis B virus, Hemophilus influenzae type B (H. influenzae), human papillomavirus (HPV), Japanese encephalitis, measles, Neisseria meningitidis serogroup A (meningococcus), Streptococcus pneumoniae (pneumococcus), rotavirus, rubella, and yellow fever.
“We find that immunization programs in the 98 countries considered will result in individuals born in 2019 experiencing 72% lower mortality due to those ten pathogens over their lifetime than they would with no immunization,” Li and colleagues wrote. “Furthermore, in the absence of vaccination, we estimate that all-cause mortality among children younger [than] 5 years would be 45% higher than currently observed. These impacts are a testament to both the public health benefit of vaccines overall and the sustained investment in increasing global vaccination coverage in the past two decades. They also highlight what might be lost if current vaccination programs are not sustained, and thus provide quantitative evidence supporting both donor and country investments in vaccination programs.”
The results of their modelling study suggest that increasing HPV coverage in girls will avert more deaths per person vaccinated than any other immunization activity, and that increasing pneumococcus coverage will give the largest reductions in mortality among children younger than 5 years, they added.
Writing in a commentary accompanying the study, Adam L. Cohen, MD, MPH, of the Center for Global Health at the CDC, Minal K. Patel, MD, of the Division of Immunization, Vaccines, and Biologicals at WHO, and Thomas Cherian, MD, of MM Global Health Consulting in Geneva, applauded the study by Li et al for highlighting “the large impact of vaccination and how well the global immunization community and caregivers have done in vaccinating children,” adding that the current modelling study likely underestimates the full impact of vaccination. However, they also warned that the global community is in danger of losing these gains.
“Despite the success of vaccination globally, people are still dying from [vaccine-preventable diseases],” they wrote. “The Covid-19 pandemic has interrupted immunization services and compromised health systems in many countries. Low vaccine coverage before the Covid-19 pandemic was leading to a resurgence in VPDs, such as measles. This decline in coverage together with vaccine skepticism, which is being increasingly reported in low-income and middle-income countries, threatens to reverse the gains that have been achieved.”
The VIMC modelling study involved model-based disease burden estimates from 16 independent research groups. Disease burden was quantified by deaths and disability-adjusted life-years (DALYs) stratified by age. For their assessment, Li and colleagues compared a “counterfactual” scenario where no vaccines were administered with reported and projected vaccination scenarios.
“Two forms of aggregation were used to present the results: by calendar year and by year of birth,” they explained. “The estimates by calendar year were used to assess the difference in burden between the reported and projected vaccination and no-vaccination scenarios for a specific year and to give a cross-sectional view of impact. The estimates by year of birth were used to sum disease burden across every year of life for each yearly birth cohort (born between 2000 and 2030), and also to assess the difference between reported and projected vaccination and no-vaccination scenarios, and therefore gives a lifetime view of vaccine impact. The population-attributable benefit of vaccination for each pathogen was estimated as the proportion of annual deaths due to each pathogen that would be prevented by vaccination.”
Li and colleagues found that, from 2000-2019, there was an overall increase in the average number of vaccines received per child across the majority of the 98 LMICs, in terms of both pre-existing vaccines (e.g., measles) and vaccines introduced after 2000 (e.g., rotavirus vaccine).
“We estimate that vaccination of the ten selected pathogens will have averted 69 million (95% credible interval 52–88) deaths between 2000 and 2030, of which 37 million (30–48) were averted between 2000 and 2019,” the study authors reported. “From 2000 to 2019, this represents a 45% (36–58) reduction in deaths compared with the counterfactual scenario of no vaccination.” Most of this impact is concentrated in a reduction in mortality among children younger than 5 years (57% reduction [52–66]), most notably from measles. Over the lifetime of birth cohorts born between 2000 and 2030, we predict that 120 million (93–150) deaths will be averted by vaccination, of which 58 million (39–76) are due to measles vaccination and 38 million (25–52) are due to hepatitis B vaccination. We estimate that increases in vaccine coverage and introductions of additional vaccines will result in a 72% (59–81) reduction in lifetime mortality in the 2019 birth cohort.”
Li and colleagues pointed out limitations to their study; for example, the study did not evaluate uncertainty in demographic estimates and estimates of past and future vaccine coverage, and the analysis only included 99 LMICs. Also, they noted that, for most countries where certain vaccines were yet to be introduced, the study assumed they will reach the same coverage of a reference vaccine within 2 to 3 years, possibly leading to an overestimation of impact.
Li and colleagues added that it is “crucial” to continue to both maintain high coverage levels and further increase vaccine coverage on a global scale in order to ensure that coverage gains achieved since 2000 are not undone, an effort that “requires continued political commitment, funding, civil society engagement… improving public trust and confidence in the safety and efficacy of vaccines, and strengthening immunization programs through education, training, and supervision.”
In their commentary, Cohen, Patel, and Cherian noted that global immunization strategies, such as WHO’s Immunization Agenda 2030, will be instrumental in sustaining increases in vaccine coverage, including with new vaccines such as those against Covid-19.
“Global leaders and the immunization community can use the findings of Li and colleagues to inform renewed efforts to ensure everyone receives all their vaccines on time throughout their life,” they wrote. “If this happens, the next run of these models will show that many more lives have been saved due to vaccination.”
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A modelling study from the Vaccine Impact Modelling Consortium found that increasing vaccine coverage for 10 pathogens in low- and middle-income countries has prevented an estimated 37 million deaths from 2000-2019, and this number is projected to increase to 69 million by 2030.
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The results of this study suggest that increasing HPV coverage in girls will avert more deaths per person vaccinated than any other immunization activity, and that increasing pneumococcus coverage will give the largest reductions in mortality among children younger than 5 years.
John McKenna, Associate Editor, BreakingMED™
The Vaccine Impact Modelling Consotrium (VIMC) is supported by Gavi and the Bill & Melinda Gates Foundation, and the study was funded by Gavi, the Vaccine Alliance, and the Gates Foundation.
Consortium members received funding from Gavi and the Gates Foundation via VIMC during the course of the study. Study authors reported grants and other funding from WHO, the Gates Foundation, the John C. Martin Foundation, AbbVie, Gilead, Intercept, Pan American Health Organization, the Association of State and Territorial Health Officials, and others.
Cohen, Patel, and Cherian declared no competing interests.
Cat ID: 31
Topic ID: 79,31,730,31,138,44,192,925
