How have vaccines improved public health in the US?

Measles, mumps, and polio are supposed to be diseases of the past. In the early to mid-20th century, scientists developed vaccines that effectively eliminated the risk of anyone getting sick or dying from illnesses that had killed millions over millennia of human history.

Vaccines, alongside sanitized water and antibiotics, have marked the epoch of modern medicine. The US was at the cutting edge of eliminating these diseases, which helped propel life expectancy and economic growth in the postwar era. Montana native Maurice Hilleman, the so-called father of modern vaccines, developed flu shots, hepatitis shots, and the measles-mumps-rubella (MMR) vaccine in the 1950s and ’60s, which became virtually universally adopted among Americans.

Smallpox, the most common form of which has a 30-percent fatality rate, has been eradicated. Mitch McConnell, Republican titan of the Senate, may be the last major public figure still afflicted by a childhood case of polio, less than a century after it paralyzed a sitting American president. Measles likely infected millions of people annually in the US in the 1800s, although precise estimates from the era are hard to come by. In the early 1990s, thousands of people died from the disease every year. It was still infecting more than half a million and killing hundreds per year on average in the 1950s and ’60s, before the vaccine debuted. Diphtheria, a deadly respiratory infection, killed more than 1,800 people annually between 1936 and 1945 as the vaccine against it was still being rolled out. Today, it has not killed anybody in the United States in decades.

The vaccines that made this possible are among the most important achievements in human history. And yet many Americans appear to be losing faith in them, a worrying trend that could accelerate if President-elect Donald Trump succeeds in handing control of the top US health agency into the hands of Robert F. Kennedy Jr., the country’s foremost vaccine denier.

Kennedy has spent much of his public career pushing the thoroughly debunked theory of a link between autism and childhood vaccines. He has supported an anti-vaccine group in Samoa, where measles vaccination rates have since fallen off; a 2019 outbreak killed 83 people just a few months after Kennedy visited the island and met with anti-vaccine advocates. He has likewise cast doubt on the safety and efficacy of the Covid vaccines, a position that helped nudge the lifelong Democrat toward Trump. After RFK Jr. dropped his own presidential campaign this year, he became Trump’s most influential health adviser and last week was nominated by the president-elect to lead the Department of Health and Human Services (HHS).

The day after Trump’s election, Kennedy insisted he would not “take away anybody’s vaccines.” Instead, he said, he planned to compile vaccine safety information so that people could make their own decisions. But vaccine safety has been extensively studied — and the negative effects Kennedy claims remain undetected. (Others in Trump’s orbit have stated that Kennedy will nevertheless use whatever information he finds to try to pull vaccines from the market.)

Experts fear that his appointment will validate his anti-vaccine attitudes — and exacerbate the public’s growing ambivalence toward these vital public health measures.

As long-accepted, lifesaving public health measures increasingly become politically polarized, routine vaccination rates are rapidly declining in much of the US. In the 2019-2020 school year, three states had less than 90 percent of K-12 students vaccinated against measles, mumps, and rubella. By the 2023-2024 school year, 14 states had fallen below that threshold. The number of states with more than 95 percent of schoolchildren vaccinated — the preferred level of coverage to prevent outbreaks — dropped from 20 to 11 during that same period.

It is no surprise then that the number of US measles cases more than quadrupled from 2023 to 2024. Nobody has died of measles in the US since 2015, but if vaccination rates continue to decline, this highly contagious disease (one person can infect more than a dozen other people) will spread with increasing ease, which raises the risk that American kids could die.

We know how to prevent that. We’ve had remarkably safe, effective shots for decades. We just need to keep using them.