But how well do vaccination campaigns work in the world?

Vaccines are one of the most powerful tools for substantially reducing mortality and are among the most cost-effective health interventions.

In addition to the direct protection provided to vaccinated individuals, high levels of vaccination coverage offer indirect protection (herd immunity) to the remaining unvaccinated individuals in a population.

The World Health Organisation (WHO) introduced the Expanded Programme on Immunisation in 1974. This programme, which was supported by UNICEF and global donors, succeeded in delivering substantial increases in the coverage of routine childhood vaccines: for example, global coverage of three doses of diphtheria-tetanus-pertussis (DTP3) vaccine increased from just over 20% in 1980 to over 75% in 1990.

The last two decades have seen further expansion of childhood immunisation programmes in low- and middle-income countries (LMICs). But how well did they work?

A research team tried to answer this. An attempt was made to estimate the deaths and disability-adjusted life years (DALYs) avoided by vaccination against 10 pathogens in 98 LMICs.

Acquiring data from 2000 to 2020, the researchers provided a picture of:

hepatitis B virus, Haemophilus influenzae type B, human papillomavirus, Japanese encephalitis, measles, Neisseria meningitidis serogroup A, Streptococcus pneumoniae, rotavirus, rubella and yellow fever.

Using demographic and vaccination coverage data, the impact of vaccination programmes was determined by comparing model estimates from a no-vaccination scenario against a vaccination scenario.

Using mathematical models, the team estimated that vaccination would prevent 69 million deaths between 2000 and 2030, including 37 million between 2000 and 2019. Looking at the decade up to 2019, this would have represented a 45% reduction in deaths compared to the no vaccination scenario. Most of this impact is concentrated in a reduction in mortality among children under 5 years of age, particularly from measles.

Increased vaccination coverage and the introduction of new vaccines in LMICs have had an important impact in reducing mortality. These public health benefits are expected to increase in the coming decades if progress in increasing coverage is sustained.

Researchers also estimated that future increases in vaccination coverage and the introduction of additional vaccines will result in a 72% reduction in lifetime mortality in the 2019 birth cohort.

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