Merck used to proudly state on its website that one MMR vaccine provided lifetime immunity to 95% of those who received it.
Which makes one wonder why 100% have to have a second MMR. There are no studies that I could find that showed how many of the remaining 5% developed immunity from the second shot. I know quite a few people (adults and children) whose doctors insisted on giving them SEVERAL repeat doses of MMR, of varivax, and others, because tests showed they weren't immune to those diseases.
In spite of thousands of reports to VAERS of severe MMR reactions (including many who WERE compensated in US vaccine court), the CDC does not suggest a titer--a blood test to determine immunity.
I would like to make sure everyone reading here learns that a positive titer is accepted in every state in lieu of a vaccine.
If your child got an MMR as an infant, you may ask your doctor for the blood work to be done, or you may choose to do it on your own and pay out of pocket, and probably avoid the second MMR.
You also have the option of delaying the first one until your child is ready to enter school.
I would suggest, however, that you not combine it with any other vaccine, as vaccines in combination have never been properly tested for safety.
For adults, if you got the MMR as a child (or had measles), and your doctor suggests that you need another one (because the immunity resulting from MMR, like all vaccines, is proving to be much shorter-lived than originally anticipated), you can likewise request a titer.
We took DD's titres when she was 5--she was "immune" to measles and chicken pox--whatever that means. The difference, now, is that many states are now requiring two doses of mumps (or, two MMRs) whereas before they were requiring two doses of measles and one MMR. Of course, the single-antigen vaccine is no longer available. So, since the mumps vaccine has much lower than a 95% immunity (which is why they're requiring two and/or three mumps vaccines now), kids could get stuck with more MMRs even if they are immune to measles.
I've often asked why people don't check titres more often. The fact that they can be expensive doesn't even come up most of the time. It's more that the titres are painful (the blood draw and the kids freak out), a pain (they have to explain to the doctors what they need, and go to a different location for blood draws), and the shots are just easier (and "what's wrong with getting shots anyway?") I don't know anyone, besides us, who have actually had titres drawn.
I gave my 13 yo ds, 10 & 8 yo dd 1 dose of MMR last summer. Nurse practicioner at MinClinic said she hated giving MMR because it is one of the most painful to receive. When my hubby had to go for a cholesterol draw, I had him take the older two who agreed that getting a titer test would be much better than getting a second MMR. The 8 year old declined, but thought that the kids' report sounded better than another. We are waiting for the need to arise again.
We use an internet based blood testing service to order the titers. Private dr labs, or something, it was on retail me not. A friend of mine whose daughter was going to a large impersonal state U also did this too. She got the first shot and a titer check in a month. When the child is old enough to understand, they opt for the draw.
Rember, your state's vaccine registry will keep up with the shots, not the titers. We opted out of the state oversight and keep our records in a fire safe.