Measles vaccines protect against more than just measles. Here's how.

A doctor's assistant prepares 11-month-old Tijana for a vaccine against measles, rubella, mumps, and chicken pox in Berlin, Germany, in 2015. PHOTOGRAPH BY SEAN GALLUP, GETTY

A doctor's assistant prepares 11-month-old Tijana for a vaccine against measles, rubella, mumps, and chicken pox in Berlin, Germany, in 2015. PHOTOGRAPH BY SEAN GALLUP, GETTY

Measles is spiking worldwide, UNICEF announced on March 1, with 98 countries reporting more cases in 2018 than in the prior year. Spread through the air, measles is highly contagious, and the virus can linger in a room for up to two hours after an infected person has left.

But danger lurks even for those who survive an outbreak. Measles not only weakens your immune system in the short term, bouts with the virus seem to wipe your immune system's memory, causing the body to forget how to fight off things that you may have already conquered. For some people, this “immune amnesia” may linger for more than two years.

Before the introduction of the measles vaccine in 1963, it was nearly guaranteed that every child would catch it, and an estimated 2.6 million died from the disease each year. Luckily, the measles vaccine is incredibly effective, with two doses imparting nearly 97-percent protection. So why can't we get rid of the disease?

However, the data show that’s not the case: Not only did cases of measles plummet once vaccine use became widespread, but cases of other diseases dropped as well—pneumococcus, diarrhea, and more. In resource-poor regions, the decline was as dramatic as 50 percent; in impoverished regions, it dropped by as much as 90 percent.

“We actually saw the whole overall baseline for childhood mortality drop precipitously,” says Harvard's Michael Mina, an author on a 2015 study analyzing the decline. In essence, the measles vaccine seems to not only protect populations against measles, it seems to be keeping a slew of other infections at bay. And one way it may be doing this is through prevention of immune amnesia.

Read the full story on National Geographic’s website