Vaccinations have played a massive role in saving millions of lives over the past half century, the successful eradication of smallpox, certified in 1980, showcasing their immense potential to control diseases.
The momentum of the Smallpox Eradication Programme in its final years and the vision of providing life-saving vaccines to children everywhere, led WHO to establish the Expanded Programme on Immunisation (EPI) in 1974, with support from all member states.
This year, write Brian Wahl and Virginia Pitzer in The Lancet, the global health community commemorates 50 years of this momentous effort and looks ahead to maximising the potential impact of one of the most potent interventions in public health.
On the important anniversary for EPI – now called the Essential Programme on Immunisation – Andrew Shattock and colleagues report in The Lancet on modelled estimates of deaths averted, life-years gained, and years of full health gained by routine and supplementary immunisation since 1974 among children and adults.
They found that efforts implemented through the EPI have averted 154m deaths over the past 50 years. For each prevented death, the authors estimated that, on average, 58 years of life and 66 years of full health were gained. The measles vaccine was estimated to have saved more than 93.7m lives, more than any other vaccine.
Given the scale of the estimated burden of disease averted (accounting for 40% of the infant mortality reduction globally), it is likely that no other public health intervention during the past half-century has had a greater impact on reducing mortality and improving quality of life worldwide.
To estimate deaths averted by vaccines targeting 14 different human pathogens, the authors use a suite of 22 mathematical models, each of which has undergone peer review and been published elsewhere in some form.
For eight vaccines, they rely on meta-modelling to extrapolate vaccine impact to settings without previous estimates of deaths averted. Each model uses a different approach and relies on its own set of assumptions and limitations.
In addition, the authors acknowledge they could not account for the broader benefits of vaccination later in life, such as improved nutritional status resulting from an averted infection.
Nor were they able to account for the heterologous effects associated with both live and non-live vaccines.
Double counting deaths averted – the concept that a single life could potentially be saved multiple times – can make interpreting the results of such analyses difficult. Despite the inherent challenges in synthesising results and accompanying uncertainty from such a diverse set of mathematical models, this study provides a valuable and comprehensive assessment of the global impact of vaccination on mortality over 50 years.
The number of severe cases and hospitalisations prevented through vaccination is clearly substantial but remains unquantified. Moreover, the economic benefits of the EPI are likely to be equally impressive.
By preventing disease, immunisation programmes have the potential to save hundreds of billions of dollars in healthcare costs and contribute to substantial gains in lifelong productivity.
Healthy children are more likely to attend school, grow up to join the workforce, and contribute to their communities, leading to long-term economic growth and development.
Although these broader societal benefits were not directly quantified in the analysis by Shattock and colleagues, they underscore the far-reaching impact of vaccination beyond the prevention of morbidity and mortality.
Despite tremendous progress in recent years, global vaccination coverage regressed during the Covid-19 pandemic.
Disruptions to routine immunisation services have resulted in large immunity gaps, threatening to reverse decades of progress achieved through EPI. Investing in campaigns to reach those missed by vaccination, especially with measles vaccination, and efforts to strengthen and integrate delivery systems, will be essential to ensure that no child is left behind.
Within these efforts, immunisation programmes must prioritise equity, including efforts to reach zero-dose children who have not received a single dose of any routine vaccine. These children often live in underserved communities and difficult-to-reach settings.
Protecting zero-dose children is critical, as they are at the highest risk of contracting and dying from vaccine-preventable diseases, and their vulnerability perpetuates cycles of poverty and inequity.
Trust in immunisation programmes has eroded recently, fuelled in part by the spread of misinformation and disinformation, posing additional challenges to achieving high vaccine coverage.
Conflict zones and areas with political instability also face unique barriers to delivering vaccines.
If these and other challenges can be overcome, the future of vaccination and EPI could hold tremendous promise. New vaccines that provide protection from several substantial causes of morbidity and mortality in all ages are already or could soon be available.
These include currently available vaccines against human papillomavirus and typhoid fever, which are only now being widely rolled out in low-income and middle-income countries; new vaccines against respiratory syncytial virus that are now approved for use in the USA and Europe; and long-awaited vaccines against malaria that have been recently developed and are starting to be deployed.
Updating and bolstering systems to deliver vaccines effectively to people of all ages, including adults, will be a substantial challenge but an opportunity to extend the benefits of vaccination to all.
The Covid-19 vaccine delivery effort has provided valuable lessons for adult vaccination.
Exciting new technological developments in vaccine development and manufacturing could also revolutionise the future of immunisation and EPI. mRNA vaccines, which had a crucial role in addressing the pandemic, are exciting for three key characteristics: they are safe, effective, and have the potential for inexpensive and scalable manufacturing.
Other promising vaccine innovations include nanoscale patterning platforms, microarray patches, and advances in heat-stable vaccines.
Ensuring these new technologies address health inequities will require proactive action to support a broad base of manufacturing capacity and improved vaccine delivery systems.
Additionally, the development of therapeutic vaccines for cancer and other non-infectious diseases could revolutionise the scope and impact of vaccination efforts.
As we mark the 50th anniversary of EPI, we acknowledge the many lives saved and the immeasurable impact of vaccination. Looking ahead to the next 50 years, the global health community can envision a world where the effects of diseases like HIV, many cancers, and several neurodegenerative disorders could become but a memory – as is now the case with smallpox.
Study details
Contribution of vaccination to improved survival and health: modelling 50 years of the Expanded Programme on Immunisation
Andrew Shattock, Helen Johnson, So Yoon Sim, Austin Carter, Philipp Lambach, Raymond W Hutubessy, et al.
Published in The Lancet on 2 May 2024
Summary
Background
WHO, as requested by its member states, launched the Expanded Programme on Immunisation (EPI) in 1974 to make life-saving vaccines available to all globally. To mark its 50-year anniversary, we sought to quantify the public health impact of vaccination globally since the programme's inception.
Methods
In this modelling study, we used a suite of mathematical and statistical models to estimate the global and regional public health impact of 50 years of vaccination against 14 pathogens in EPI. For the modelled pathogens, we considered coverage of all routine and supplementary vaccines delivered since 1974 and estimated the mortality and morbidity averted for each age cohort relative to a hypothetical scenario of no historical vaccination. We then used these modelled outcomes to estimate the contribution of vaccination to globally declining infant and child mortality rates over this period.
Findings
Since 1974, vaccination has averted 154m deaths, including 146m among children under five of whom 101m were infants younger than 12 months. For every death averted, 66 years of full health were gained on average, translating to 10.2bn years of full health gained. We estimate that vaccination has accounted for 40% of the observed decline in global infant mortality, 52% in the African region. In 2024, a child under 10 years is 40% more likely to survive to their next birthday relative to a hypothetical scenario of no historical vaccination. Increased survival probability is observed even well into late adulthood.
Interpretation
Since 1974 substantial gains in childhood survival have occurred in every global region. We estimate that EPI has provided the single greatest contribution to improved infant survival over the past 50 years. In the context of strengthening primary healthcare, our results show that equitable universal access to immunisation remains crucial to sustain health gains and continue to save future lives from preventable infectious mortality.
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