In the year 2000, measles – a childhood disease that once plagued millions – was declared essentially dead in the United States. Most of today’s parents never had it, nor have their children. But there were 222 cases in the U.S. last year (up from an all-time low of 37 in 2004), and 27 more cases reported as of this spring. With vaccination rates dipping here as anti-vaccine sentiment grows, a resurgence of measles abroad and summer travel in full swing, experts worry that measles could stage a comeback.

Why Resurgence is Possible

“Measles is the most contagious disease known in humans,” says Gregory Poland, M.D., a vaccinologist at the Mayo Clinic who has studied measles for two decades. In fact, if you were born before 1957 when the first vaccines were developed, doctors assume you’ve had it. The virus is spread easily on the air – via mucus droplets sneezed or coughed out by an infected person (just like colds and flu). An unvaccinated person walking into a room where a person with measles has been, even eight hours before, will likely get measles, too.

At one time, there were around 3.4 million cases in the U.S. every year. Around 48,000 people were hospitalized by the disease; 1,000 were permanently disabled when measles led to a brain infection called encephalitis; and around 450 to 500 died – usually from either encephalitis or pneumonia.

When a vaccine was perfected in 1963, the measles rate began to drop. In fact, in 1992, the vaccination rate had reached 94 percent and was still climbing.

But in 1998, the well-respected British medical journal The Lancet published an article by a physician named Andrew Wakefield, who claimed there was a link between the measles vaccine and the rising incidence of autism. Frightened parents began refusing to vaccinate their children. And despite the facts that Wakefield’s work was discredited, Wakefield was stripped of his medical license, and the article was retracted by The Lancet in 2010, the vaccination rate today sits at 95 percent (and lower among some groups of families who are against the vaccine). Health experts say that’s a risky level.

Not a Trifling Illness

If you think of measles as just another childhood rash with red spots, think again. Measles can cause fever as high as 106º F, brain damage, and a respiratory infection that can turn into life-threatening pneumonia.

“Measles wasn’t a trifling illness, and it isn’t a trifling illness even now in 2012,” says Jane Seward, M.P.H., a deputy director at the Centers for Disease Control’s National Center for Immunization and Respiratory Diseases. One-third of Americans who got measles last year were hospitalized, and a 2-year-old in Minneapolis almost died. “He was so sick,” says Seward. “It was really touch-and-go for a week whether he was going to make it.”

There are no drugs available to treat measles or its complications. “Even with the best of modern care, about three of 1,000 who get measles die,” notes Poland. Many more are seriously injured.

The vaccine, however, is effective. Almost all measles cases in the U.S. today are brought in by unvaccinated people either coming from, or coming back from, other countries – half from Europe. There were 15,000 reported cases of measles in France last year and seven deaths. In the United Kingdom, where measles was once thought eradicated, the disease is again widespread. Closer to home, Quebec reported more than 900 cases of measles in 2011.

People with measles are contagious for up to four days before the telltale rash develops. Because it looks like a common upper-respiratory infection in its early stages, many U.S. doctors aren’t on the lookout and misdiagnose it at first.

Vaccination More Important Than Ever

With summer vacation in full swing, and travelers moving in and out of busy airports – especially those headed to the Summer Olympic Games in London at the end of July – experts worry that measles immunity in the U.S. has dropped to a dangerous level.

Clyde Martin, a mathematician from Texas Tech University, analyzed a 1987 measles epidemic in Lubbock, Texas, and found that it takes an immunity rate of 98 percent to prevent an epidemic of the disease in densely populated areas. Prior to his study, experts believed a 90 percent vaccination rate was enough.

Martin had measles around 60 years ago, when he was in second grade. He was sick and feverish for two weeks. “It was awful,” he says. “I remember being deathly ill. I was delirious a lot of the time, and I can remember my mother sitting there with a cold cloth, trying to bring my temperature down.”

Martin is concerned about communities across the country where vaccination rates have fallen dangerously low, leaving people with compromised immune systems and babies too young for the vaccine vulnerable. “They are just setting themselves up for a catastrophe,” he says.

Traveling This Summer?

If you’re vacationing this summer, even within the U.S., it makes sense to check your family’s vaccination status. “You can be exposed at an airport to someone from anywhere in the world,” says CDC’s Seward.

In the U.S., people usually get their first dose of MMR vaccine – which prevents measles, mumps and rubella – at 12 months of age. But the CDC now recommends that children traveling outside the U.S. get their first dose beginning at 6 months. Everyone ages 12 months and older should have had two doses of the vaccine.

Seward says that part of the reason vaccination rates aren’t where they should be is that people – including many doctors – don’t understand how bad things could get. “They’ve never seen measles. They’ve never seen polio. They’ve never seen quarantine signs outside of people’s houses,” she says.

And without the vaccine, it wouldn’t take long until there were once again 3-4 million cases of measles a year in the U.S. “If everyone stopped vaccinating,” Seward says, “measles would be back.”

Christina Elston is a senior editor and health writer for Dominion Parenting Media.

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Anti-Vaccine Arguments

Along with the now-discredited measles vaccine-autism connection first published in and then retracted by The Lancet, the anti-vaccine movement often cites three additional arguments.

In an April article published in Human Immunology and entitled “The Clinician’s Guide to the Anti-Vaccinationists’ Galaxy,” Mayo Clinic vaccinologist Gregory Poland, M.D., and co-author Robert Jacobson, M.D., declared these arguments as myths and offered the following rebuttals:

Myth: The bodies of infants and young children can’t respond safely to the large number of antigens (substances that cause the body to produce antibodies) given in vaccines.

Fact: Children encounter far more antigens in the natural environment than they ever encounter in vaccines, and newer vaccines expose children to fewer antigens that older versions do.

Myth: Vaccines can cause autoimmune diseases such as type 1 diabetes, multiple sclerosis and Guillain-Barre syndrome.

Fact: A 2011 Institute of Medicine review of more than 12,000 published reports failed to find evidence that vaccines cause any of these diseases.

Myth: Natural immunity is better than vaccine-induced immunity.

Fact: To gain natural immunity, a child has to be infected with a disease. And the risk of complications from infection are far greater than any risk from exposure to vaccines.

Parents who refuse vaccines create pockets of unprotected children in their communities, says Poland. “You’ve now provided tinder,” he says, “for that spark that will come.”

– Christina Elston