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Measles: What You Should Know

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Johns Hopkins Children’s Center infectious disease experts Julia McMillan and Aaron Milstone provide answers to some common questions.

young boy getting a shot

Stories about the ongoing measles outbreak have saturated our public and private space, dominating news media and social outlets and sparking lively water cooler discussions.

In a sea of information from various sources — some of them reliable, some of them less so — many parents continue to seek a better understanding of the disease and vaccinations.

Johns Hopkins Children’s Center infectious disease experts Julia McMillan and Aaron Milstone provide answers to some common questions.

If most people are immunized, how do outbreaks happen?

Measles is a highly contagious viral infection—one of the most contagious of all known infections. Nine out of 10 unimmunized children who are in contact with an infected person will contract the virus. The virus can linger in the air for about two hours after a person with measles has left the room. It can infect those who enter the room thereafter if they are unimmunized.

Because most people are immunized, measles has not occurred in the United States since 2000 except when it has been brought here by a person infected in another country. In the United States, the vaccine is not given to infants under 1 year of age because they are too young to be immunized.

Vaccines are also not given to those with deficiencies of the immune system. These individuals are all susceptible to measles infection if they are exposed. A growing number of people in the United States opt out of measles immunization because of personal preference. When one or two infected people come into contact with a population that includes unvaccinated people, the virus can spread rather quickly.

Isn’t measles one of those diseases that everyone used to get as a child? My grandmother says that when she was a kid, she and all her siblings got it, and they’re just fine.

At best, measles is a very uncomfortable illness. At worst, it can be lethal. Most commonly, the infection causes high fever, cough, conjunctivitis (red, runny eyes), runny nose, and a rash that begins on the face and eventually covers the entire body. The illness lasts about a week if there are no complications.

When complications do occur they can include ear infections, croup, pneumonia, and encephalitis or inflammation of the brain that can lead to permanent neurologic damage and even death. On average, measles kills between one and three of every 1,000 infected children.

What if we’re exposed to someone with measles? If my child has been immunized, is there any cause for concern?

The measles vaccine creates lasting protection in 95 percent of children who receive one dose of it and in 99 percent of those who receive the second dose. It is extremely rare for an immunized child to develop infection after exposure to someone with the disease.

What about my baby, who is only partially through his or her immunization schedule?

Even a single dose of the vaccine is highly effective in preventing infection. Under usual circumstances, the measles vaccine is recommended to be given at 12 to 15 months and again 4 to 6 years of age. If exposure to measles is likely, however, either because of planned travel to an area where measles occurs more frequently, or because of possible exposure during an outbreak, the second dose can be given as soon as one month after the first, leading to 99 percent protection.

In addition, under circumstances in which exposure is more likely, infants between 6 and 12 months of age can be immunized. Because the vaccine is less effective when given at that age, an infant who receives measles vaccine before 1 year of age should later receive two additional doses under the regular schedule.

I’ve read that vaccines can cause unwanted side effects. Should I be concerned?

The measles vaccine is extremely safe. Some children — about 10 percent — will develop a fever about six to 12 days after vaccination, and an even smaller percentage will develop a rash that can last a few hours to a day or two. In extremely rare cases, the fever can precipitate a seizure in children predisposed to fever-induced seizures. Scientific research has shown unequivocally that the measles vaccine does NOT cause autism or other permanent neurologic or developmental problems.

Can the measles vaccine cause full-blown infection?

The vaccine contains a live but weakened form of the measles virus designed to create immunity without causing full-blown illness. In children with normal immune systems, the vaccine will not cause full-blown measles.

A tiny percentage of children born with defective immune systems may develop a measles-like illness after receiving the vaccine. If the immune deficiency is diagnosed in time, such children should not be vaccinated. Because a small number of people and young infants cannot receive the vaccine due to age or other illness, it is critically important that the rest of the population is vaccinated to prevent outbreaks and spread of the disease.