By Denise Grady New York Times News Service
Measles has been spreading in the United States at a rate that worries health officials.
Most infections are linked to an outbreak that began in Disneyland in December, almost certainly started by someone who brought the disease in from another country.
A “smattering” of other imported cases have also occurred, according to Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention.
Measles was eliminated from the United States in 2000, meaning that the infection no longer originates here. But worldwide, there are still about 20 million cases a year; in 2013, about 145,700 people died of measles.
Travelers can bring the virus into the United States and transmit it to people who have not been vaccinated.
Measles spreads through the air and is among the most contagious of all viruses; in past epidemics, it was not uncommon for one patient to infect 20 others.
Some 90 percent of people exposed will get sick (unless they are immune because they have had measles already or have been vaccinated).
The virus can hang suspended in the air for several hours, so it is possible to catch measles just by walking into a room where an infected person has recently spent time.
Inhaling a tiny amount of viral particles is enough to cause illness.
The disease is cause for particular concern because it can have severe complications, including pneumonia and encephalitis, which can be fatal.
Those who survive encephalitis can wind up with brain damage.
Measles can also cause deafness.
And even without complications, the virus makes children very sick, with high fevers, a rash and sore eyes.
Painful ear infections are also common.
Here are some commonly asked questions about measles and the vaccine that prevents it.
Has the United States been particularly hard-hit?
Many relatively wealthy countries are having worse outbreaks.
Virtually all of continental Europe has been undergoing a large outbreak since 2008, with more than 30,000 cases in several years.
France, which gets more tourists than any other country, had 15,000 measles cases in 2013, with at least six deaths.
About 95 percent of the cases were in people who had never been vaccinated or had not had both recommended doses.
In the United States, vulnerable communities have had outbreaks in the last few years, including Orthodox Jews in Brooklyn, N.Y., and the Amish in Ohio.
But vaccination rates are also relatively low in some wealthy, liberal neighborhoods.
The Seattle suburb of Vashon Island is believed to have the lowest vaccination rates of any health district in the country.
Who is most at risk of becoming seriously ill from measles?
Babies and young children who have not been vaccinated are most vulnerable, and most at risk for dangerous complications.
“Even in developed countries like the U.S., for every thousand children who get measles, one to three of them die despite the best treatment,” Schuchat said during a recent news teleconference.
In the United States from 2001 to 2013, 28 percent of young children with measles needed to be treated in the hospital.
In pregnant women who have never been immunized or never had measles, the disease increases the chance of premature labor, miscarriage and having a baby with a low birthweight.
People with leukemia and other diseases that weaken the immune system are also at risk of severe illness from measles.
The best protection for high-risk people, Schuchat said, is a high rate of vaccination in everyone else, so the disease cannot gain a foothold and start spreading.
Is the measles vaccine safe?
There is no evidence that the vaccine causes harm.
Research in 1998 linking it to autism was proved fraudulent and was retracted.
Children may briefly run a low fever — an increase of about 1 degree Fahrenheit — after the shot and may develop a mild rash.
When should children get the measles vaccine?
They need two shots: one when they are 12 to 15 months old and another when they are 4 to 6 years old, according to the CDC.
The injections contain a mix of vaccines to prevent measles, mumps and rubella.
Why do babies have to wait until they are a year old to receive the vaccine?
During the first year of life, infants may carry antibodies from their mothers that can prevent the vaccine from working, so the shot is delayed.
But if there is a risk of exposure — say, from international travel — the first shot can be given at 6 months and is thought to provide some protection.
But those babies will need two more shots: the second at 12 months and the third at least 28 days later.
How long does it take the measles vaccine to start working?
The shot usually provides protection in 10 days to two weeks.
How effective is the measles vaccine?
More than 95 percent of people will become immune after receiving one dose, according to the CDC. With two shots, the efficacy reaches about 97 percent.
The vaccine does fail in a small percentage of people for unknown reasons.
One possible cause is mishandling of the vaccine; failure to keep it cold can inactivate it.
Is there anyone who should not receive the measles vaccine?
Pregnant women and people with weakened immune systems and with certain illnesses are among those who should not be given the measles vaccine.
The CDC maintains a detailed list on its website of conditions in which the measles vaccine should be postponed or avoided.
I don’t know if I’ve ever had measles or the measles vaccine. What should I do?
The easiest solution is to be vaccinated. Even if you had been vaccinated, there is no harm in getting another shot.
Measles vaccine is always given in combination with the mumps and rubella vaccines.
People born before 1957 are assumed to be immune to measles, because the disease was so common in the prevaccine era that virtually everyone caught it and became immune.
It is possible to have a blood test that will look for measles antibodies, which would indicate that you had had measles or the vaccine, and therefore are immune.
But testing would require two doctor visits and a wait for lab results.
Just getting the shot is simpler, easier and cheaper.
Is it safe to stretch out the immunization schedule so babies do not receive more than one or two vaccines at a time?
Some parents fear that multiple vaccinations will overwhelm an infant’s immune system.
But infectious-disease experts say there is no reason to stretch out the vaccination schedule or to worry that a child’s immune system cannot handle multiple vaccines administered at one time.
“From the moment the child enters the world through the birth canal, that child’s immune system is being stimulated by all kinds of bacteria,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University.
“The child is constantly being stimulated, and that’s the way the child’s immune system was designed by nature to work and become competent.”
A child’s immune system can easily respond to all the vaccines given according to the standard schedule recommended in the United States, Schaffner said.
He warned that stretching out the schedule was not only unnecessary, but may endanger children by lengthening the time during which they are susceptible to the diseases that vaccines can prevent.
Do people catch measles from animals?
No. It is strictly a disease of humans.