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As measles cases climb, some Americans might need another shot

As authorities work to contain a measles outbreak sweeping across the country, health officials recommend Americans receive two doses of the Measles, Mumps and Rubella (MMR) vaccine -- or verify that they have received two doses in their lifetime.

Knowing your vaccination status, however, can be tricky and may require learning a bit about the history of measles in the United States.

Most Americans born before 1957 are likely to have been infected naturally and therefore are presumed to be protected against measles, mumps and rubella, according to the U.S. Centers for Disease Control and Prevention. Before the measles vaccination program started in 1963, an estimated 3 to 4 million people got measles each year in the United States.

In 1968, an improved and even weaker measles vaccine was developed, and it has been the only measles vaccine used in the United States since being distributed, according to the CDC.

Following implementation of the one-dose measles vaccine program, there was a "rapid and significant reduction" in reported cases in the United States through the 1980s, the CDC said. By the late 1980s, however, measles outbreaks were still occurring among school-aged children who had received a single dose of measles vaccine.

In 1989, a two-dose vaccination schedule was adopted in the United States.

So what does that all mean for you, now, in 2019? Anyone vaccinated between 1963 and 1989 would likely have received only one dose.

According to public health officials, those unable to verify if they've received two doses of measles immunization should talk to their doctor. Some may need two doses.

Adults who are going to be in a setting that "poses a high risk for measles transmission" should make sure they have had two doses separated by at least 28 days, which includes students at post-high school education institutions, health care personnel and international travelers, the CDC says.

"If you're unsure whether you've been vaccinated, you should first try to find your vaccination records. If you do not have written documentation of MMR vaccine, you should get vaccinated," the CDC states on its website. "The MMR vaccine is safe, and there is no harm in getting another dose if you may already be immune to measles, mumps, or rubella."

Additionally, many who were vaccinated prior to 1968 with the earlier version of the vaccine made from an inactivated (killed) virus should be revaccinated "with at least one dose of live attenuated measles vaccine."

"This recommendation is intended to protect those who may have received killed measles vaccine, which was available in 1963-1967 and was not effective," the CDC states online.

The CDC says one dose of the MMR vaccine is 93 percent effective against measles, while two doses are 97 percent effective.

Children typically get their first dose between 12 and 15 months of age and get their second dose around 4 to 6 years of age. Parents should immunize children at 6 months of age or older if they will be traveling internationally, the CDC says.

Measles symptoms don't appear until 10 to 14 days after exposure, health officials say. The highly contagious virus can spread to others through coughing and sneezing.

Symptoms include cough, runny nose, inflamed eyes, sore throat, fever, and a red, blotchy skin rash.

Approximately 704 measles cases have been reported in the U.S. since Jan. 1, the highest number since 1994 and since measles was declared eliminated in 2000, according to the CDC.

Nearly 800 students, faculty and staff members were quarantined last week following exposure to the measles virus at two Los Angeles universities, and officials in New York closed schools, issued fines and lobbied the legislature to eliminate religious exemptions for required vaccinations.