The Unbiased Science Guide on MMR Vaccines and Measles Titer Tests

Because now is not the time to mess around with protection!

We have been getting a ton of questions from people about early MMR vaccine doses, uncertainty of vaccination status for adults, and whether titer tests are necessary—and Unbiased Science has you covered! Two medical doctors, an immunologist, and a public health scientist put together this practical guide that we hope will address your questions and concerns. Whether you're wondering about your own vaccination status or trying to make decisions for your family during the current measles outbreak, we've compiled the most essential information to help you navigate these important health decisions.

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KEY POINTS AT A GLANCE:

• People with uncertain vaccination status can safely be vaccinated without first checking titers.

• Two doses of MMR vaccine provide approximately 97% lifetime protection against measles.

• Antibody titers are generally unnecessary if vaccination history is known.

• Do not delay vaccination if you are unvaccinated or uncertain of your status.

Adults: Do you need an MMR dose?

If you were born before 1957, you likely had measles naturally as a child and have lifetime immunity. You generally don't need vaccination or antibody testing.

If you've received two documented doses of the MMR vaccine at any point in your life, you're considered protected against measles. You don't need additional doses or antibody testing during an outbreak.

If you're unsure about your vaccination status, it's safe to get an MMR vaccine. There's no need to check your antibody levels (titers) first - getting vaccinated is a simpler and effective approach.

Adults: Do you need an MMR dose? (continued)

A special note for those vaccinated between 1963-1967: During this period, some people received an inactivated measles vaccine that was later found to be less effective. However, not everyone vaccinated during this time needs a booster, as many received the more effective live attenuated vaccine. If you're concerned and were vaccinated during this time, consult with your HCP.

Measles Vaccine Manufacture and Distribution in the United States (1963–2016)

Created by Unbiased Science

Table generated using data from:

1. “Measles Vaccine Failure.” Clinical Pediatrics, vol. 18, no. 3, Mar. 1979, pp. 161–67. DOI.org (Crossref), https://doi.org/10.1177/000992287901800309.

2. Strebel, Peter M., et al. “37 - Measles Vaccines.” Plotkin’s Vaccines (Seventh Edition), edited by Stanley A. Plotkin et al., Elsevier, 2018, pp. 579-618.e21. ScienceDirect, https://doi.org/10.1016/B978-0-323-35761-6.00037-7.

FYI: In the US, MMR is only available as a combination vaccine that protects against measles, mumps, and rubella. Monovalent vaccines (those that protect against just one disease, such as measles alone) are not available in the US. There is no evidence that separating these vaccines provides any benefit, and the combination MMR vaccine has an excellent safety record and effectiveness profile.

Children and MMR Vaccination Timing

The standard MMR vaccination schedule for children includes a first dose at 12-15 months of age and a second dose at 4-6 years (before starting kindergarten). Children who have followed this schedule and received both doses are considered protected.

The first dose is recommended at 12 months because maternal antibodies that cross the placenta during pregnancy can remain in the baby's circulation for at least 6 months (possibly up to 9 months). If a baby receives the vaccine while these maternal antibodies are still present, the antibodies will neutralize the vaccine antigens, making the vaccination less effective. By waiting until 12 months, we ensure these maternal antibodies have cleared from the baby's system.

Can Kids Get Early Doses of MMR?

For infants 6-11 months old in outbreak areas or traveling internationally, healthcare providers may recommend an early dose of MMR vaccine. This early dose doesn't count toward the routine schedule, and these children will still need their regular doses at the recommended ages.

For children aged 1-4 years who have only received their first dose, healthcare providers might recommend giving the second dose early (at least 28 days after the first dose) if they live in or are traveling to an outbreak area.

Antibody testing (aka titer test) for measles is typically unnecessary.

Many people wonder if they should get their antibody levels (titers) checked to confirm immunity. For most people, this step is unnecessary if you know you've had two doses of the MMR vaccine.

Titers can be expensive, can take time to process, and most importantly, may be misleading in determining your true protection against measles.

Let's discuss...

Titer levels for measles may be misleading.

The science behind measles immunity is complex. While there is an established threshold for protection in laboratory testing, this lab cutoff isn't perfectly reliable. More importantly, your immune system works in multiple ways to protect you!

Memory B cells, which provide long-term protection against measles, don't continuously produce antibodies. They activate when needed to fight infection. This means you can have low measles antibody levels but still be protected because your memory B cells are ready to respond if exposed. Cell-mediated immunity (another part of your immune system that typically refers to T cells) also provides protection even when antibody levels appear low.

Antibodies Don't Tell the Whole Story.

If you've had your antibodies tested and received a positive result, you're considered protected regardless of how high above the threshold your levels are. While higher numbers generally indicate stronger antibody response, being above the threshold is what matters for protection.

A key point: Even if your titer test shows a 'negative' or 'low' result, this doesn't necessarily mean you need another MMR dose if you've already had two documented doses. This is precisely why routine titer testing isn't recommended for people with documented vaccination - it can lead to unnecessary additional doses without providing meaningful protection beyond what you already have.

Should anyone not get the MMR vaccine?

While the MMR vaccine is safe for most people, certain groups should not receive it:

• People who are pregnant

• People with severely compromised immune systems, such as those with certain cancers, advanced HIV infection, or those taking medications that significantly suppress the immune system.

• People who have had a severe allergic reaction (anaphylaxis) to a previous dose of MMR vaccine or an ingredient in the vaccine.

• Anyone with a moderate or severe acute illness should wait until they recover before getting the vaccine.

People with these conditions should consult their HCP about their specific situation, especially during a measles outbreak when the risk of infection may be higher.

MMR Vaccine & Titers: Bottom Line

If you've received two doses of MMR vaccine in your lifetime, you can be confident that your immune system is well-equipped to fight measles through multiple layers of protection. Two doses of MMR vaccine are expected to provide approximately 97% lifetime protection against measles infection.

As we are in an active measles outbreak, do not delay or take chances. If you're unsure about your vaccination status, get vaccinated now – additional doses are safe. Antibody testing during an outbreak only delays protection and is typically unnecessary for fully vaccinated individuals.

People with uncertain vaccination status can safely get the MMR vaccine without first checking antibody levels.

We hope this helps! Drop additional questions in the comments.

Stay Curious,

Unbiased Science

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