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.

Read the full article about vaccines by Dylan Matthews at Vox.