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What's in a Measles Vaccine?

Measles vaccines are made using a "live" virus.
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Many people who resist getting measles vaccines say they’re worried the ingredients are toxic, or might harm them or their children.

People have been asking the question since the first vaccine came out, but it’s making headlines again with the outbreak of measles linked to Disneyland. It’s affected more than 100 people in 14 states and the count will go up before it’s over.

Measles vaccines are made using what’s called an attenuated virus. That means it’s been weakened in the lab. It’s grown in cultures of chick embryos — basically, unhatched live eggs. Lots of vaccines are grown that way — it’s old-fashioned technology but it works. Because the chicks are partly developed, people with egg allergies can safely receive the vaccine.

When you’re injected with the vaccine, that weak virus sets up an infection that activates the immune system.

“What a vaccine does is it gives the immune system practice so that if it encounters a germ it can destroy it.”

“Our immune system functions like an army or a police force,”says Dr. Walt Orenstein, a vaccine expert at Emory University who is a former assistant surgeon general and former head of the United States Immunization Program. “What a vaccine does is it gives the immune system practice so that if it encounters a germ it can destroy it.”

But mild infection is not usually enough to make you sick — although one in six people can run a low fever, and one in 20 get a mild rash.

They are not strongly contagious, and there' no evidence anyone recently vaccinated with a measles vaccine has ever infected anyone else. However some doctors say people with weakened immune systems such as cancer patients recovering from bone marrow transplants shouldn’t get any live vaccine and should keep their distance from anyone who’s recently had one.

About one in 3,000 people who get the MMR vaccine suffers a seizure, although it’s not usually dangerous, the Centers for Disease Control and Prevention says.

Most people get the vaccine in a "cocktail" that protects against measles, mumps and rubella (MMR), also known as German measles. The mumps component of the vaccine is also a live virus grown in chick cells, while the rubella component is grown in lab dishes containing human lung cells.

The viruses are further cultured in a broth made using salt, vitamins, amino acids and a little bit of serum — the liquid part of blood — from a calf fetus. Sugars and a human blood component called albumin are mixed in, as well as neomycin, an antibiotic used because it rarely triggers allergies. It helps keep stray germs from growing in the vaccine. Gelatin is mixed in as a stabilizer.

“Each dose of the vaccine is calculated to contain sorbitol (14.5 mg), sodium phosphate, sucrose (1.9 mg), sodium chloride, hydrolyzed gelatin (14.5 mg), recombinant human albumin (≤0.3 mg), fetal bovine serum (less than one part per million), other buffer and media ingredients and approximately 25 micrograms of neomycin. The product contains no preservative,” the package insert reads.

“It is all out there for people to look it up if they want to.”

“If people want to check the ingredients, they are on the Food and Drug Administration FDA website and in the package insert. Nothing is being hidden,” Orenstein said.

“It is all out there for people to look it up if they want to.”

Health officials say the measles vaccine is one of the safest out there. The U.S. government maintains a program called the National Vaccine Injury Compensation Program. It pays damages to people who can show they’ve been injured by a vaccine.

Since 1988, 889 claims of injury have been filed for MMR vaccine injuries through the program and most have been dismissed after investigations. But 367 people were paid.

“We continue to monitor safety,” says Orenstein. “It’s not like it’s in a test tube today and out there tomorrow. It goes through all these phases of clinical trials, and then we continue to monitor the safety even after it’s on the market. We allow physicians and even parents to report adverse events.”