Q. I thought measles was all but eradicated in the United States. Why is it back?
A. There are two main reasons. First, though significant progress has been made in reducing global measles incidence, there is still substantial circulation of the virus in other countries. Unvaccinated U.S. residents who travel to countries where measles is widespread or epidemic, and unvaccinated residents of those countries who travel to the United States, are bringing the virus here.
Second, a large number of parents in this country are hesitant or refuse to have their children vaccinated, and that has resulted in an accumulation of unvaccinated populations who can become infected and maintain transmission.
As a result, a virus that was declared eliminated in the U.S. in 2000 infected 644 people across 27 states in 2014. This year is already on pace to exceed that number, if current trends continue. Through January 30 there have been 102 people from 14 states reported to have measles. Most of these people had not been vaccinated. Most of these cases are part of an ongoing outbreak linked to a Disneyland visitor from outside the U.S.
Q. How contagious is measles?
A. It's one of the most contagious of the vaccine-preventable diseases. The average person with measles would be capable of infecting 12 to 18 other people if all his or her contacts were susceptible (either because they were unvaccinated or because they were in the small percentage of people for whom the vaccine isn't effective). That's far greater than the contagion rate for influenza or chickenpox. And the rate of transmission to susceptible household members is 75 percent. That means that if you are infected with measles and live with four unvaccinated people, three of them will likely also get the measles. Like many other viruses, measles is spread mainly through respiratory droplets from coughing, some of which can remain in the air of an hour or two, and via surfaces that may be contaminated with those droplets.
Q. If I was vaccinated against the measles decades ago, do I need a booster?
A. If you had only one shot of MMR (measles, mumps, and rubella vaccine), you could consider getting a second one, though it's not essential. A single MMR shot provides 95 percent protection, meaning 95 percent of people who get it will develop immunity to measles; a second shot ups the protection to 97 to 99 percent. If you don't have a record of being vaccinated as a child or having had measles, and you were born in 1957 or after, talk with your doctor about how many doses of MMR you might need.
Q. How effective is the vaccine?
A. Very. In the decade before the measles vaccination program began in the late 1960s, an estimated 3 to 4 million people in the United States were infected each year, of whom 400 to 500 died, 48,000 were hospitalized, and another 1,000 developed chronic disability from measles encephalitis (a brain infection). By 2011, in contrast, widespread use of measles vaccine had led to a greater than 99 percent reduction in measles cases in this country. Globally, measles vaccination prevented an estimated 15.6 million deaths between 2000 and 2013 alone.
Q. Can someone be infected with measles without showing symptoms?
A. Yes. It takes about 2 weeks on average for symptoms to appear once a person has been infected. They usually become contagious around the same time that symptoms appear. The main initial symptoms are a cough, runny nose (similar to a head cold), fever, and red, watery eyes. White spots in the mouth (called Koplik's spots) may develop a couple of days after symptoms start, followed by a skin rash on the third to fifth day.
Q. Are there people who can't get vaccinated against measles?
A. Yes, some. Severely immunocompromised individuals, including people on immunosuppressive drugs, may have to avoid measles vaccination; they should check with their doctors. Infants can't get the vaccine until they're at least 6 months old, and the first dose usually isn't given until between 12 and 15 months, unless the child will be traveling abroad. So those groups are especially susceptible to measles infection.
This post was originally featured on Berkeley Wellness .