Measles

How contagious is measles?

Measles is extremely contagious, with about 90% of exposed, susceptible individuals progressing to infection. The period of contagiousness is on average nine days.

How dangerous is measles?

The severity of a measles infection varies, and is somewhat determined by maturity of an individual’s immune system. Young children under five, adults over 20, pregnant women, and people with compromised immune systems are most vulnerable to complications. The hospitalization rate of measles infections is about one in four. Pneumonia is the most common complication among those hospitalized.

How well does the MMR vaccine work?

If given after 12 months of age, the first dose provides immunity in about 93% of individuals. The majority 90% of those 7% initial nonresponders develop immunity with a second dose. If the vaccines are given on schedule, protection is about 97%.

What’s the typical immunization schedule and why?

The first dose is usually given between 12-15 months of age in America, with the second dose following at ages four-to-six. The second dose can be given as early as 28 days after the first dose.

Until around six months, newborns of vaccinated mothers have maternal antibodies, which can interfere with the desired immune response of the vaccine. For this reason, the first dose is delayed to provoke a more robust immune response in the vaccinated infant. Vaccine success rate is higher at 12 months (close to 95% effective) than at nine months (close to 85%). Ultimately, ideal vaccination timing may be best determined by examining the following factors: local variation in birth rate, seasonality, and access to care.

Given the recent outbreak, are there situations where vaccinations can or should be given sooner?

With a local US outbreak, infants in areas of concern should be vaccinated at six months to confer protection (in addition to the 12-15 month and four-to-six year shots), though that initial dose will not make all of them immune. In some parts of the world, the first shot is given at nine months, which projects an immunity rate of about 85%.  

Additional recommendations would be to vaccinate at the beginning of the usual 12-15 month window for older infants and to consider providing the dose usually given at four-to-six years as early as 28 days after the dose usually given at 12-15 months.

What about for international travel?

Non-vaccinated infants aged 6-12 months can get their first dose early, subsequently followed by the normal two dose schedule, for three doses total. This is the same schedule that is recommended for those involved in a local outbreak.

What is “evidence of immunity”?

According to the CDC, preschool-age children and low-risk adults need written documentation that they’ve received one or more doses of a measles-containing vaccine given on or after their first birthday.

School-age children and high-risk adults (college students, healthcare professionals, and international travelers) need laboratory evidence of immunity, laboratory confirmation of measles, or a birthday before 1957.

Is there a way for someone who’s not sure if they’re vaccinated or whether they got both doses to test their antibodies?

Yes, there is a blood test that can validate or invalidate immunity. It’s called a titer or IgG (a type of antibody) level for the virus. We can order this test for you if there is concern about your immunity. Insurance coverage, as with most lab tests, is variable.

Are there any risks with the shot?

There is a small risk (1 in 2500 to 1 in 4000, depending on age) of febrile seizures in children receiving the vaccine. Febrile seizures are something that some children experience in response to high fevers, which do not have negative long-term consequences. There is also a small risk (1 in 40,000) of lowered platelet count in the six weeks post vaccination. MMR vaccines do NOT contribute to development of autism, which sometimes has presenting symptoms near the same age as MMR vaccination.

Are there any typical symptoms/side effects to the shot?

As with most other vaccines, the most common side effects are sore arm (at injection site), rash, fever, and body aches (muscles and joints).

Are there people who should not get it?

Pregnant women, people with a previous life-threatening reaction to MMR vaccine, people with rare immunocompromised conditions, people with a current tuberculosis infection, and people who have received transfused blood or blood products in the past three months shouldn’t get the vaccination, according to the CDC.