How Vaccines Transform Global Health: 103 Million Cases Prevented

Many infectious diseases, such as whooping cough, measles, and hepatitis, can be fatal. Preventing them through vaccines has saved countless lives.

Other infections, although they don’t always cause death, can leave serious long-term effects. Poliomyelitis, for example, can cause paralysis; rubella in newborns can lead to blindness, deafness, or heart problems. Preventing these diseases not only saves lives but also avoids devastating consequences that can be permanent. Vaccines, therefore, protect both life and quality of life.

A study published in the prestigious New England Journal of Medicine by researchers at the University of Pittsburgh revealed that, since 1924, vaccines have prevented 103 million cases of eight contagious diseases. These include smallpox (completely eradicated), measles, polio, rubella, mumps, hepatitis A, diphtheria, and pertussis. In the last ten years alone, according to the study, vaccination has prevented more than 20 million cases.

The disease with the highest number of cases prevented was diphtheria, with more than 40 million cases avoided. As for measles, the vaccine has prevented approximately 35 million cases.

The study also showed how the statistics reflect the impact of vaccination: measles cases declined rapidly after the vaccine was introduced. Cases of rubella and mumps also declined, although more gradually. The most notable effect was observed in 1978 with the introduction of the MMR vaccine, which protects against measles, mumps, and rubella.

Despite these achievements, some of these diseases are making a resurgence. The increase in cases is partly due to many people choosing not to get vaccinated or to vaccinate their children, considering vaccination optional. In 2025, for example, the highest number of measles cases in recent years was recorded.

Dr. Donald Burke, a professor at the University of Pittsburgh’s School of Public Health, explains that when vaccines are highly effective and prevent so many cases, “people stop fearing diseases and underestimate the importance of vaccines, something we are unfortunately seeing today.”

The University of Pittsburgh’s Project Tycho collected statistics from the late 19th century, analyzing 125 years of data (since 1888) on the number of cases reported before and after the development and widespread use of each vaccine. The database was built from the weekly reports of the Centers for Disease Control and Prevention (CDC). This project was funded by the National Institutes of Health (NIH) and the Bill & Melinda Gates Foundation.