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The Informed Parent

Why Two Doses of MMR and Chickenpox Vaccines?

by Louis P. Theriot, M.D., F.A.A.P.
Published on May. 03, 2017

Mrs. X was bringing her 18-year-old daughter in for a physical in order to register her for college. It turns out that Zoe had never been seen in our office before. Mom explained, “You have seen my other two children as they are much younger. But since we moved to the area Zoe has been very healthy and has had her sports physicals done at her high school.”

Zoe was in excellent condition and had a perfectly normal exam. When reviewing her immunization card from the previous doctor I noticed that she had only one measles-mumps-rubella (MMR) vaccine and one chickenpox vaccine (Varivax). All her other vaccines were complete. Mom seemed stunned that Zoe might be missing some. “I am a strong believer in vaccinating my children and can’t understand why she would be lacking,” she said in disbelief.

I told her that in the past we used to give one MMR and one Varivax at one year of age. For many years now the schools have required two vaccines…one given at a year of age, and another at four to five years, before kindergarten. The schools are strict about this. It is possible that Zoe fell through the cracks when she was entering kindergarten as it was not widely enforced.

Mrs. X said emphatically, and much to the displeasure of Zoe, “I want her to get these boosters right away; certainly before she goes out of state for college!” I proceeded to explain about these vaccines and why Zoe may NOT need to get them. This generated a sigh of relief from the young lady.

The second dose of the MMR and Varivax are actually not booster shots. When one receives one dose of the MMR at a year of age they are 93% protected against measles and 78% protected from mumps. When they get a second dose of MMR the protection goes up to 97% against measles and 88% against mumps. With one dose of Varivax the protection against chickenpox is 85% and with two shots it goes up to 90-98%. So the second doses are not really boosters. They are to increase the likelihood of protection.

I told Mrs. X that we had two options for Zoe. We could give the vaccines, or we could measure the protection she had from the first set of MMR and Varivax that she received at a year of age. We could measure the antibody titers for measles, mumps, rubella and varicella (chickenpox). If they were in a protective range it would prove that she was fully protected with the vaccines she already received. She would not need a second vaccine. Zoe really liked this idea because she invariably faints when she get shots.

Mom showed me the form that the college required. Sure enough it asked for her immunization status and had a section asking for the two dates of her MMR and varivax vaccines. I told mom I would fill out the physical portion and put the form in her chart. When we got the results of the blood test I would fill in the appropriate information and she could pick it up at her convenience. It usually takes a few days to get the results.

Three days later the results showed that Zoe had high levels of protection against measles, mumps, rubella and varicella. Zoe knew that if the levels were insufficient she would need to get the vaccines. She was more than willing to take the chance. It worked out for her. I was able to complete the form stating that while she only had one MMR and varivax she was shown to be fully protected and I attacked a copy of her lab results to the form. At the end of the day when I finally made it back to my desk, there was a hand written note from Zoe thanking me for sparing her from having to get two shots. It put a smile on my face.

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