After clean water, vaccines are widely considered to be the greatest contribution to human health. Ever. Nothing in history has killed more people than the arsenal of infectious diseases – from familiar ancient enemies to newly emerging pathogens – against which vaccines provide a widening umbrella of protection (Streefland, 2001; Lee, 2020; Nnaji et al, 2021). No other public health intervention provides comparable societal benefit for the same per capita cost (Jit et al, 2015; Doherty et al, 2016).

In the last two decades, vaccines are estimated to have prevented 2.7 million cases of measles annually, 2 million cases of neonatal tetanus, 1 million cases of pertussis, 600,000 cases of paralytic poliomyelitis and 300,000 cases of diphtheria, averting 2– 3 million deaths worldwide each year (Remy et al, 2015; Kennedy, 2019).1 Between December 2020 and December 2021, COVID vaccinations are estimated to have averted between 14.4 and 19.8 million deaths (Watson et al, 2022).

National immunisation programmes in the United States since 1980 have seen a decline of greater than 92 per cent in cases and 99 per cent in deaths from diphtheria, mumps, pertussis and tetanus – entirely eliminating endemic polio, rubella and measles (until recent resurgence of the latter) – preventing 33,000 deaths and 14 million cases of disease in each birth cohort, saving USD$10 billion in direct costs and $33 billion in disability and lost economic productivity (Roush et al, 2007).

In the early 1960s, roughly a third of African children died before their fifth birthday – most killed by infectious diseases like smallpox and measles. Vaccine coverage in developing countries was abysmal, widely in single figures. In the decades following the launch in 1974 of the Expanded Programme on Immunisation aggregate rates of national coverage for a basic schedule of routine vaccines rose steeply to between 80 per cent and 90 per cent, and vaccine-preventable mortality plummeted (Figure 5.1) (Greenwood, 2014).

Between 2000 and 2016, measles-related deaths fell by 84 per cent, averting 20.4 million avoidable deaths. Smallpox has been eradicated – the first instance in human history of a natural pathogen removed from the ecosystem. Between 1988 and 2013, the rate of death among newborns as a result of preventable tetanus fell 94 per cent from 787,000 to 49,000 a year.