The measles vaccine arrived in two forms, a decade apart

The first measles vaccine was licensed in the United States in 1963. It was an inactivated vaccine, made from measles virus that had been killed in the laboratory. This vaccine worked, but it had a significant drawback: immunity faded over time, and vaccinated people could still catch measles years later—sometimes with unusually severe symptoms.

A better version followed in 1968. The live attenuated measles vaccine used a weakened form of the virus instead of a killed one. This version produced stronger, longer-lasting immunity. The 1968 vaccine is essentially the same one used today, though it is now combined with vaccines for mumps and rubella into a single shot called the MMR vaccine.

The shift from the inactivated to the live vaccine happened quickly in the United States. By the early 1970s, the older version was no longer in use domestically, though some other countries continued using it for longer.

Key Takeaways

  • The first measles vaccine was licensed in 1963 and used killed virus, but immunity did not last as long as doctors hoped.
  • A live attenuated vaccine became available in 1968 and provided stronger, longer-lasting protection.
  • The 1968 vaccine was combined with mumps and rubella protection to create the MMR vaccine, which remains the standard today.
  • Measles cases in the United States dropped dramatically after vaccination became widespread, from hundreds of thousands per year to near zero by the 2000s.

Why the 1963 vaccine did not stay in use

The inactivated vaccine protected people in the short term, but the protection weakened significantly within a few years. More troubling, some vaccinated people who later encountered the wild measles virus developed what researchers called atypical measles—a modified form of the disease that could be severe and unusual in its presentation.

This problem did not emerge immediately. It became apparent only after vaccinated children were exposed to measles in the community years later. The combination of waning immunity and the risk of atypical measles made the inactivated vaccine less attractive once a better option existed.

How the live vaccine worked better

The live attenuated vaccine used measles virus that had been weakened through repeated growth in laboratory cell cultures. This weakened virus could still infect cells and trigger an immune response, but it could not cause the full disease in healthy people. The immune system's reaction to the live virus was stronger and more durable than its reaction to killed virus.

The live vaccine also did not carry the atypical measles risk. People vaccinated with the live vaccine who later encountered wild measles were protected by genuine, lasting immunity rather than by the incomplete protection the inactivated vaccine offered.

The impact on measles cases in the United States

Before any vaccine existed, measles infected nearly every child in the United States. In the early 1960s, before widespread vaccination, the country saw hundreds of thousands of measles cases annually. The disease killed several hundred people per year, mostly infants and young children.

After the live vaccine became available and vaccination rates climbed through the 1970s and 1980s, measles cases fell steeply. By the 1990s, cases had dropped to the hundreds per year. By the early 2000s, measles was so rare in the United States that the disease was declared eliminated—meaning no continuous transmission within the country.

This elimination lasted until vaccination rates declined in certain communities in the 2010s and 2020s, which allowed measles to return in localized outbreaks. But the baseline remains: the vaccine introduced in 1968 has prevented millions of cases and thousands of deaths over five decades.

Why measles vaccine development took until 1963

Measles virus was identified in 1911, but developing a working vaccine took more than 50 years. The main obstacle was that measles virus is difficult to grow in the laboratory. Researchers needed to find cell cultures where the virus would replicate reliably without killing the cells too quickly.

In the late 1950s and early 1960s, scientists finally developed reliable cell culture methods. John Enders and his colleagues grew measles virus in human and animal cell cultures, then weakened it through serial passage—growing it repeatedly until it lost its ability to cause disease. This work led directly to the 1963 inactivated vaccine and the 1968 live vaccine.

The MMR combination and later developments

By the late 1960s, vaccines for measles, mumps, and rubella were all available separately. In 1971, these three vaccines were combined into a single injection called the MMR vaccine. The combination made vaccination simpler—one shot instead of three—and improved the likelihood that children would receive all three vaccines.

The MMR vaccine has remained largely unchanged since then, though manufacturing processes have been refined. A second dose was added to the standard schedule in 1989 to catch the small percentage of children who did not develop immunity after the first dose. This two-dose approach has kept measles elimination in place in the United States for decades, despite the virus circulating elsewhere in the world.

Frequently Asked Questions

Why did it take so long to develop a measles vaccine?

Measles virus grows poorly in laboratory conditions and was difficult to culture reliably until the late 1950s. Once scientists developed better cell culture methods, vaccine development moved relatively quickly—the inactivated vaccine appeared within a few years, and the improved live vaccine followed five years later.

Is the measles vaccine still the same one from 1968?

The live attenuated vaccine strain used today is descended from the one licensed in 1968, but manufacturing and purification have improved significantly. The vaccine is now combined with mumps and rubella protection in the MMR shot, and a second dose is given to ensure immunity in nearly all recipients.

Could the inactivated vaccine have been improved instead of replaced?

Possibly, but the atypical measles problem and waning immunity made it a less attractive target for improvement. The live vaccine solved both problems at once, so research and public health efforts focused on that approach instead.

What happened to measles after the vaccine became common?

Measles cases dropped from hundreds of thousands annually in the early 1960s to near zero by the 2000s in the United States. The disease was declared eliminated in 2000, though outbreaks have occurred in recent years when vaccination rates declined in specific communities.