Vaccinations for 10 major diseases have prevented the deaths of 37 million people in nearly a hundred low- and middle-income countries since the turn of the century, according to a new modeling study. The news comes amid widespread hesitancy around COVID-19 vaccines, which are starting to roll out in several countries, reminding the world of just how important vaccines are for us.

Side effects: Might save your life

Vaccines have been responsible for substantial reductions in mortality and are among the most cost-effective health interventions in the world, the authors of a new study point out . In addition to direct protection provided to vaccinated individuals, high levels of vaccination coverage offer indirect protection (herd immunity) to the remaining unvaccinated individuals.

The timescale of vaccine impact varies considerably. For some childhood diseases (such as measles, rotavirus, and pneumococcal disease), the impact is seen rapidly, whereas, for human papillomavirus (HPV) and hepatitis B, vaccine impact is commonly seen over a much longer timescale in the reduction of adult morbidity and mortality. Caroline Trotter, a co-author of the study, said in a statement:

“There has been a much-needed investment in childhood vaccination programs in low-income and middle-income countries and this has led to an increase in the number of children vaccinated. To inform future investment and ensure it continues we need to evaluate the impact of these programs on public health.”

The Vaccine Impact Modelling Consortium, a collaboration of 16 research groups, created estimates from at least two independent models, for each of ten diseases. The estimates focused on deaths averted by vaccination against 10 diseases in 98 countries, two-thirds of the world’s population, in the period 2000-2030.

The 10 diseases the researchers focused on were: Hepatitis B, Haemophilus influenzae type b (Hib), human papillomavirus (HPV), Japanese encephalitis, measles, meningitis A (Neisseria meningitidis serogroup A), pneumococcal disease (Streptococcus pneumoniae), rotavirus, rubella, and yellow fever. Vaccinations against such diseases prevented 37 million deaths between 2000 and 2019, of which 36 million were deaths averted in children under the age of 5 years, according to the Consortium’s findings. A further 32 million deaths will be prevented by 2030 due to vaccine programs, of which 28 million are deaths averted in under-5s.

Measles vaccination had by far the largest estimated overall impact, the study showed, with 33 million estimated deaths prevented in the period 2000-2019. This represents over 1.6 million deaths averted per year. The researchers also anticipate this will increase to over 2.1 million deaths averted per year in the period from 2020 to 2030.

“Our study signifies the huge public health benefits that can be achieved from vaccination programs in low-income and middle-income countries,” the study’s corresponding author Neil Fergurson said in a statement. “By projecting up until 2030 in these 98 countries we have provided insight on where investments in vaccine coverage should be directed to achieve further gains.”

Above those already achieved, the largest potential additional gains will be seen by increasing HPV vaccination coverage in girls, the study showed. This is predicted to avoid more deaths per person vaccinated than any other immunization activity. Increasing pneumococcal conjugate vaccine coverage will give the largest reductions in under-5 mortality.

The researchers also highlighted what could be achieved by further investment in vaccination programmed by countries and donors. Priorities should include increasing coverage of vaccines against HPV and pneumococcal disease. Continued funding, investment, political commitment, and strengthened health systems are needed to sustain the gains already seen.

Still, the study has some limitations, especially since many of the countries selected don’t have complete or consistent data on disease burden and death. In the countries where certain vaccines were yet to be introduced the study assumed they will reach the same coverage as a reference vaccine, which may lead to an overestimation of impact.

But regardless of these uncertainties, one thing’s for sure: millions of children and adults have been saved by vaccines, and it’s a remarkable scientific triumph.

The study was published in the journal The Lancet.