Q&A: MMR & MMRV Safety

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Anonymous Asks: I’ve heard there is a new version of the MMR shot that includes the chickenpox vaccine too. My son will be getting his one year shots soon, and I’d like to know if the new version is safe.

Our Answer: Thanks for your question! Yes, there are now two options for children age 12 months to 12 years when it comes to protecting them from measles, mumps, rubella and varicella: Using the combination MMR vaccine plus the stand alone varicella vaccine in two separate injections, or a combination that contains all four, called MMRV.

Children need to receive two doses of vaccine to protect them against these four diseases.

The first is recommended at age 12­15 months, the second is recommended at ages 4­6 years. The recommendations differ for the first and second dose, based on what we know about the side effects. For the first dose, in the child’s second year of life (age 12­24 months) either option can be given, however, the CDC recommends using MMR and varicella separately, rather than the combination MMRV vaccine. Giving MMRV together requires one less injection, but there are data that suggest that MMRV when given for the first dose (between ages 12-­23 months) is associated with a slightly higher risk of fever (102 or higher) within 42 days after the vaccine is given, especially within 5­12 days, as well as a slightly higher risk of febrile seizures during that time compared to those who get the separate MMR and varicella vaccines at the same visit.

Studies show that the MMRV combination is associated with fever in about 22 out of every 100 children vaccinated, versus about 15 out of every 100 children vaccinated when the separate MMR + varicella vaccines are used. Likewise for febrile seizure, MMRV is associated with febrile seizure in about 8 out of every 10,000 children vaccinated vs. 4 out of 10,000 children vaccinated when MMR + varicella are used.

Febrile seizures are seizures caused by a high fever. 2­5% of children under 5 years will have at least one, and they are most common in 14­18 month olds. As MMR and varicella are live attenuated vaccines, it is not uncommon for the child’s immune system to mount a fever as it responds to the vaccine (which is a good thing actually, it means the vaccine is doing it’s job of ‘tricking’ the immune system into thinking it’s the real virus and therefore is creating protective antibodies). It is believed that febrile seizures occur in young children because the brain is still learning how to cope with fever.

It’s important to note that while febrile seizures can be extremely distressing for parents, they are usually not associated with any long term complications. Children should be evaluated by a physician, but invasive testing and medication are not usually required, unless a more serious underlying condition, like epilepsy, is suspected or found. Febrile seizures can run in families. If your child has a family history of febrile seizures, be sure to discuss this with your pediatrician.

For children ages 4­6, the data do not suggest an increased risk of fever or febrile seizures with MMRV vaccine compared to those receiving MMR and varicella separately (whether for the first or second dose). Therefore there is no basis for a scientific or medical preference for MMR and varicella separately vs. MMRV combination in this age group. However, the combination MMRV requires one less injection, and so may be preferable to parents (or their toddlers!).

Further Reading:

Red Wine & Applesauce on MMR versus MMRV side effects.

CDC info on MMRV:

Q&A on MMR and MMRV from the CDC.

Pediatrician’s Fact Sheet on MMR and MMRV from the CDC.


Photo credit to njxw. Creative Commons license.