It is almost hard to believe just how effective vaccines are at saving infants’ lives.

The world has become a much safer place to be a young child in the last 50 years. Since 1974, infant mortality worldwide has plummeted. That year, one in 10 newborns died before reaching their first birthday. By 2021, that rate had fallen by over two-thirds.

A lot of factors drove this change: lower poverty and better nutrition, cleaner air and water, and readily available antibiotics and other treatments. But one of the biggest contributors, a new study from the World Health Organization (WHO) concludes, was vaccines.

Vaccines alone, the researchers find, accounted for 40 percent of the decline in infant mortality. The paper — authored by a team of researchers led by WHO epidemiologist and vaccine expert Naor Bar-Zeev — estimates that in the 50 years since 1974, vaccines prevented 154 million deaths.

Of that 154 million, 146 million lives saved were among children under 5, including 101 million infants. Because the averted deaths were so concentrated among young people, who on average would go on to live for 66 years, vaccines gave their beneficiaries an astounding 9 billion additional years of life.

The paper was commissioned on the 50th anniversary of the WHO’s Expanded Programme on Immunization, which launched in 1974 to build on the success of the agency’s work eradicating smallpox. It covers a critical period of time. The previous decades had seen a spree of important, newly developed vaccines: a joint diphtheria, pertussis, and tetanus vaccine in 1948, a polio vaccine in 1955, a measles vaccine in 1963. While rolled out quickly in wealthy countries, these immunizations were, as of 1974, not broadly available in the Global South, even as the diseases they prevented wreaked massive damage.

Over the ensuing half-century, through vaccination campaigns led by the WHO and later Gavi (a multilateral group formerly called the Global Alliance for Vaccines and Immunization), that changed radically. In sub-Saharan Africa in 2021, 68 percent of 1-year-olds received a first dose of the measles vaccine, 78 percent received the tuberculosis vaccine, and 70–71 percent received the vaccines against hepatitis B, polio, and diphtheria/tetanus/pertussis.

This progress yielded massive gains. The measles vaccine, in particular, deserves pride of place in this story. The researchers conclude that it averted 93.7 million deaths from 1974 onward, accounting for the most deaths averted by vaccines in general. In terms of lives saved, the runners-up — tetanus (28 million saved), pertussis (13.2 million), and tuberculosis (10.9 million) — pale in comparison. Stamping out measles through vaccination enabled it to go from an omnipresent, fast-spreading lethal threat to a relic of the past — though anti-vaccine activists threaten to undo some of that progress.

The data is a reminder that vaccines have historically been one of our best tools for saving lives and that redoubling efforts to discover and distribute new ones for diseases like malaria and tuberculosis could have a similarly transformative effect.

How the researchers tracked the benefit of vaccines

Studying the effect of vaccines across all continents, and across a 50-year time frame, is a daunting project. It’s not for nothing that this paper has 21 authors. (And let’s give them the credit they’re due. They are: Andrew Shattock, Helen Johnson, So Yoon Sim, Austin Carter, Philipp Lambach, Raymond Hutubessy, Kimberly Thompson, Kamran Badizadegan, Brian Lambert, Matthew Ferrari, Mark Jit, Han Fu, Sheetal Silal, Rachel Hounsell, Richard White, Jonathan Mosser, Katy Gaythorpe, Caroline Trotter, Ann Lindstrand, Katherine O’Brien, and Naor Bar-Zeev.)

The paper is essentially combining three separate kinds of data and research results:

1. Actual infant, child, and overall mortality across countries from 1974 to 2024, based on the UN World Population Projections dataset through 2021 as well as its projections for mortality in 2022–2024.
2. Vaccine coverage by country and year, using both WHO databases and those from the Vaccine Impact Modelling Consortium.
3. Empirically verified models of how measles, polio, hepatitis B, and several other diseases spread in the absence of vaccines, as well as estimates from the Global Burden of Disease study of the effect of vaccination on diphtheria, tetanus, pertussis, and tuberculosis.

Put simply: They used what we know about how many people got vaccinated in the last five decades and how well vaccines work to construct a version of history where all that vaccination didn’t occur, and adjusted actual death rates and health statistics accordingly.

This necessarily involves filling in some gaps in the data. They note that in many countries, our data on vaccine coverage starts in 1980, not 1974; in these places, they argue that vaccine coverage was so meager that assuming no coverage in 1974 and a steady increase thereafter is appropriate. They also conduct sensitivity analyses showing that other ways of handling this problem produce similar headline results.

The years of health life data allows another vantage point on gains from vaccination. Some diseases, like polio, are less lethal than the likes of measles but can cause lifelong negative health impacts, up to and including muscle paralysis. (For instance, while many doctors no longer think Franklin Delano Roosevelt’s paralysis was due to polio, it easily could have been.)

Any way you slice the data, vaccines saved a ton of lives and prevented a ton of suffering.

The past few years have been wonderful for vaccination, mostly due to the tremendously positive impact of the rapidly developed Covid-19 vaccines, but also somewhat perilous. In the US, the share of adults saying all children should be vaccinated against measles, mumps, and rubella has fallen, specifically among Republicans, a likely aftershock of how polarized the Covid vaccine issue has gotten. In that context, it’s important to remember just how much immunization has given us. In a half-century, it’s given people 9 billion additional years to live their lives. That’s nothing short of miraculous.