Measles: Are You Immune?

| Posted On Jul 02, 2019 | By:

illustration of measles virusIn light of international outbreaks of measles and some measles outbreaks occurring in the U.S., many people may be wondering if they need to be vaccinated or if they are immune to measles. Please see the following most “frequently asked questions” on measles and measles immunity.

Why are we suddenly seeing outbreaks of measles?

Measles is a highly transmissible infectious disease which had been previously eliminated in the U.S. in 2000. Since that time there have been outbreaks of measles primarily in “pockets” or communities where rates of measles vaccination is lower. Many outbreaks and cases of measles in the US are spread from people travelling internationally to or from areas with higher rates of measles.

Who is immune to measles?

Per the CDC, you have evidence of measles immunity if you have any one of the following:

  1. Anyone born in the United States before 1957 is presumed to be immune due to previous exposure to the virus (however, criteria does not apply to healthcare workers) OR
  2. Anyone who has documentation of two doses of measles vaccine (e.g., MMR) OR
  3. Anyone who has a positive measles serology (lab test) that shows antibody response and immunity to measles.

What should I do if I am not sure if I got measles vaccination or am immune? 

If you’re unsure whether you’re immune to measles, you should first try to find vaccination records or documentation of measles immunity. If you do not have written documentation of measles immunity, you should get vaccinated with the measles-mumps-rubella (MMR) vaccine. Another option is to have a doctor test your blood to determine whether you’re immune, but this option may take 2 visits. There is no harm in getting another dose of MMR vaccine if you may already be immune to measles, mumps or rubella.

Who needs measles vaccine?

People born after 1957 need at least one dose of measles vaccine unless you have laboratory confirmation that you had past measles infection or are immune to measles. Certain adults may need 2 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. These adults include:

How effective is the measles vaccine? 

The measles vaccine is very effective. Two doses of measles vaccine are about 97% effective at preventing measles if you are exposed to the virus. One dose is about 93% effective. The MMR vaccine is also effective for the development of immunity to mumps and rubella.

Is the measles vaccine safe?

Yes, the measles vaccine is safe. Rates of adverse reactions and side effects are extremely low with the MMR vaccine. The MMR vaccine is also safe for people who have received the vaccine previously.

Could I still get measles if I am fully vaccinated?

Very few people—about three out of 100—who get two doses of measles vaccine will still get measles if exposed to the virus. This is in contrast with estimates that approximately 90% of people who do not have immunity will develop measles in the setting of an exposure. Experts aren’t sure why there are a very small number of people who are vaccinated but are still susceptible to infection in the setting of exposure. It could be that their immune systems didn’t respond as well as they should have to the vaccine. But the good news is that fully vaccinated people who get measles are much more likely to have a milder illness. And fully vaccinated people are also less likely to spread the disease to other people, including people who can’t get vaccinated because they are too young or have weakened immune systems.

What are the symptoms of measles?

Measles looks and feels like a cold at first.  People typically develop cough, high fever, runny nose, and red, watery eyes. These symptoms start about ten days after infection. A few days after the initial cold-like symptoms, a red blotchy rash starts first on the face and then spreads to the rest of the body.

Can people get very sick from measles?

Rarely, people can develop ear infections or pneumonia, and in very rare cases (1 in 1000 cases), the virus can cause swelling of the brain. The more severe complications from measles are very rare overall.

Who is at risk for measles in the setting of a measles exposure?

People who are not immunized or under-immunized for measles are considered to be at risk in the setting of exposure. Very young children, pregnant women and persons with underlying medical conditions or on treatment with medications that compromise the immune system are also considered to be at higher risk.

Special thanks to the entire Infection Control team at Atrius Health for their contributions to this article.

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About Dr. David Yassa

Dr. Yassa received his medical degree from the University of Vermont College of Medicine. He completed his internal medicine residency at Massachusetts General Hospital and his pediatric residency at Boston Children's Hospital, followed by an infectious disease (ID) fellowship at Beth Israel Deaconess Medical Center. He is board certified in infectious disease and has an MPH from the Harvard T.H. Chan School of Public Health with a focus on clinical effectiveness. Dr. Yassa joined the Atrius Health in 2016. His clinical interests include general ID, HIV, Hepatitis C infection, mycobacterial infections, infection in immune compromised hosts, and cardiac device-related infections.

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