MMRV vs MMR + V vs M + M + M + R + V

MMRV vs MMR + V vs M + M + M + R + V

A few weeks ago, government officials were discussing MMRV (measles, mumps, rubella, and varicella), and if kids should have the shots separated into smaller components.  Some of the officials had mentioned that the MMRV has more side effects in 1 year olds than older children.  That is true.  Both Merck (the manufacturer) and the CDC found that febrile seizures were twice as likely in the group that received MMRV at 1 year old versus the group of kids who received MMR and V in two shots at 1 year old.

How many children are affected?

In CDC data, in the first 7 - 10 days after getting the MMRV 8.5 out of every 10,000 children had a febrile seizure, where 4.2 out of every 10,000 children had a febrile seizure if they had the MMR and Varicella separately (but on the same day).

In Merck’s data, in the first 5 - 12 days after getting the MMRV 7.0 out of every 10,000 children had a febrile seizure, where 3.2 out of every 10,000 children had a febrile seizure if they had the MMR and Varicella separately (but on the same day).

These numbers are likely pretty reliable because both the government and the manufacturer found similar conclusions.  In science, conclusions derived from studies are much firmer when they come from multiple independent sources.  Also, there was no difference in febrile seizures found in children four years old and older.  Regardless of cause, 97% of febrile seizures happen in children under 4 years old (CDC).

What is a febrile seizure?

A febrile seizure is a short seizure in a young child that can be caused by a variety of illnesses and occasionally the MMR/MMRV vaccine.  On CDC.gov (febrile seizures and vaccines), as of 10/5/25, says “Febrile seizures can be frightening, but nearly all children who have a febrile seizure recover quickly.  Febrile seizures do not cause any permanent harm and do not have any lasting effects.”  I have had many patients with febrile seizures over the last 23 years, and I have never had one have a permanent problem after the seizure, but what they all have in common is the seizure scares the parents badly.  Even knowing they are safe, I am sure they would have scared me if I had seen one of my two boys have a febrile seizure.  I am very sympathetic to the fear that surrounds witnessing a febrile seizure in a child, and do not want to downplay that in any way.  That said, measles and varicella both can have long lasting and sometimes fatal consequences, so the vaccines’ benefits far outweigh their risks.

Why do some pediatricians give MMRV at 1 year old and others give MMR + V?

The difference is how the pediatrician views the choice between one extra shot (MMR shot plus a Varicella shot) or a roughly 1/3000 chance of an additional febrile seizure (MMRV).  Most of us are parents, and have our own biases for what we would want for our own children.  All of us have had experiences with patients we care about.  For me personally, having witnessed how traumatized some parents are after witnessing a febrile seizure, I fell in the camp of MMR vaccine plus a separate Varicella vaccine at 1 year old well visits.  I have never done it any other way.  It doesn’t mean other pediatricians are wrong, it is just a different risk assessment!  The government recently advocated for no longer using the MMRV at the 1 year old well visit.  I received a letter from the health department today (10/6/25) that this is now a rule.

What about when the president said we should split the MMR into separate measles, mumps, and rubella vaccines and give them that way?  

The first problem with this is they don’t exist.  They haven’t existed since 2009 in the US when the MMR was found to be just as safe as the three separately, and there is no evidence that using the three separately has an advantage (Archives of Disease in Childhood 2001;85;271-274).  Using them separately, without a clear advantage, is also mean.  It would take 6 shots instead of 2 shots to give the same protection, which is 4 unnecessary needles going into our kids.  

As of 9/30/25 there have been 1544 cases of Measles in the US - the most measles we have had since the year I graduated high school, 1992.  The vast majority of these are in unvaccinated children, but everyone's risk goes up the more cases we have.  It is more important than ever to get your MMR at the 1 year and 4 year old well visit appointments.  

Thanks, Dr William Fisher