Health and Science News for Parents

Investigating side effects from the MMR and MMR plus varicella vaccines

written by Tara Haelle

Of all the childhood vaccines on the CDC’s recommended schedule, the MMR is one of the oldest, the most effective… and the most feared. That is, I hear more parents express concerns about the MMR, which protects against measles, mumps and rubella, than any other childhood vaccine, and it’s the vaccine once maligned by debunked concerns about autism (debunked literally dozens and dozens of times). I also hear a lot of hesitancy about the varicella vaccine, which protects against chickenpox, perhaps because parents don’t understand why it’s necessary and perhaps because of worries about possible but extremely rare breakthrough infections.

It’s true that both of these vaccines are associated with more reactions that parents would notice – and worry about – than most of the other vaccines on the schedule, but a recent study in Pediatrics should offer some reassurance to parents wondering whether there are rare, undetected side effects from the combined MMRV or from the MMR when given along with the varicella vaccine. Answer: there aren’t. The study confirmed the risk of the same adverse events that we already knew were linked to these vaccines, and the researchers ruled out the other studied conditions as possible outcomes and didn’t find anything new to worry about. (Though, it’s nice that they keep looking, just in case, right? This is what I love about vaccine research. It never ends, so we just keep gathering more and more data to support what we know or help us understand what we don’t. But I digress…)

No surprises here! Researchers found exactly what they should have with the MMR and the MMRV vaccines. photo by Ned Horton

No surprises here! Researchers found exactly what they should have with the MMR and the MMRV vaccines. photo by Ned Horton

First, you can read what side effects have been linked to the MMR, to the varicella vaccine and to the MMRV at the CDC website. The most serious ones for MMR and MMRV are high fever, a seizure with no lasting damage, low platelet count and, in the rarest cases, a severe allergic reaction. (The site lists other adverse events that have been reported to occur after the vaccine, but these haven’t been shown to be caused by the vaccine; they occur so rarely that it’s so far been impossible to determine. Given the millions and millions of MMR doses administered over the years, the fact of that rarity alone should be reassuring.)

This new study, published today in Pediatrics and funded through America’s Health Insurance Plans and the CDC, looked at seizures, fevers, low platelet count (resulting from a condition called immune thrombocytopenia purpura, or ITP) and allergic reactions (anaphylaxis), but it also looked for increased risk of ataxia (jerky muscle movements), arthritis, meningitis/encephalitis, acute disseminated encephalomyelitis (a neurological disease) and Kawasaki disease. The researchers compared the MMR and the MMRV from 2000 to 2012 in children aged 12 to 23 months old and enrolled in health care centers participating in the Vaccine Safety Datalink. The study involved more than 123,000 doses of MMRV and more than a half million doses of MMR plus varicella.

The good news: the researchers found no increased risk of any of these seven outcomes when comparing the MMRV to the MMR. In other words, the risk from the MMRV is no worse than the risk from MMR when it comes to the seven conditions they studied. I know, that doesn’t sound reassuring. But that’s what the point of the study was, to compare the MMRV to getting the MMR along with the varicella. And don’t worry – they also looked at the risk of these outcomes with each vaccine individually, and that’s where we get…

The better news: Other than the known link to ITP, no increased risk was seen for the other outcomes, and no new safety concerns were seen. “These estimates indicated that even if an increased risk for these outcomes exists, the risk is low and rare after either measles-containing vaccine,” the authors wrote. In fact, the risk of ataxia was actually significantly *lower* after both the MMR and the MMRV (though that’s probably a fluke and not a result of any protective effect from the vaccines).

The findings mathematically showed an increased risk for anaphylaxis (severe allergic reaction) after the MMRV, but this finding was based on only two cases, neither of which was confirmed as related to the vaccine and both of which occurred in children with a history of allergic reactions. So all this means is that two children with a history of severe allergic reactions had an allergic reaction following the MMRV that may or may not have been related to the vaccine. While the Institute of Medicine has established that the MMR and MMRV can cause a severe allergic reaction, it occurs in approximately 1.5 o 1.8 of every 1 million doses. An unvaccinated child has a much higher likelihood of catching the measles.

The bad news: The MMRV has about double the seizure risk of the MMR. But, we already knew this and the risk is still pretty low – 1 child out of 3,000 for the MMR and 1 child out of 1,250 for the MMRV, according to the CDC, which matches up with what was found in this study. The study also confirmed what we know in general: that the risk of fever and seizure is higher in the 7 to 10 days after getting either the MMR or the MMRV.

There was also an increased risk of ITP, particularly 14 to 28 days after the vaccines but also up to 42 days afterward. Yet again, we already knew that; the CDC estimates these low platelet counts occur in 1 out of every 30,000 doses. The condition goes away on its own within 6 to 12 months in 80 percent of kids and is rarely a serious or life-threatening condition.

So, today’s study is pretty unexciting, but then, that’s what we usually want from vaccine studies: nothing surprising and confirmation of what we already knew.


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13 Responses to “Investigating side effects from the MMR and MMR plus varicella vaccines”

  1. Dorit Reiss

    I didn’t see a link to the study in the post – did I miss it? Can you provide a citation?

  2. Dorit Reiss

    Thank you very much!!

  3. Elise Carroll

    Did any of the children subsequently show signs of autism? Two people I know say the vaccines “unlocked” their children’s autism subsequently.. They say their children’s behaviour changed after the seizures and allergies as a result of the vaccine, and the children are now unfortunately autistic. Any data on this? My child is due for the vaccine, and I am trying to get any reliable information i can find.

    • Tara Haelle

      This study did not identify any children who developed autism. The concern about the MMR “unlocking” autism is a common one, but it is fortunately one that the evidence has shown is not supported. There have been several dozen studies confirming no link between the MMR and autism, and this one is one more in that group. Let me know if you would like links to the others since this particular concern is probably more studied than any other in recent years.

  4. Steph

    This is kind of unrelated to the comparison of MMR and MRRV, but I’m wondering about the duration of ITP risk. The above entry says that the increased risk of ITP lasted up to 42 days after vaccination. Is that because data collection stops at some point or is enough data collected to determine if there was a lifelong increased risk of ITP?

    • Tara Haelle

      Good question. 42 days is a common risk window in vaccination studies, and I believe this is because that’s the furthest out that an adverse event is likely to be connected to the vaccination. In the case of ITP, previous studies have found an increased risk for ITP following MMR within that time frame, so it’s big enough to capture an increased risk. Here is one of those studies from 2012:

      This quote from that study may help address your question further: “Since then, the association of live attenuated measles-mumps-rubella (MMR) vaccine and ITP has been well established. ITP is known to occur after many types of infections, including numerous vaccine-preventable diseases. In approximately two-thirds of ITP cases, there is a history of a preceding infectious illness in the days to weeks before ITP onset. A subset of these children will have an identifiable virus, such as Epstein-Barr virus, varicella zoster virus, influenza virus, or HIV. Because vaccines are designed to induce an immune response that mimics natural infection to produce immunologic protection, it is theoretically possible that vaccines besides MMR could trigger ITP.” That’s what that particular study was testing — whether other vaccines could also cause ITP. They found that only the MMR and MMRV are linked to ITP, but that also means that it’s a temporary condition induced by the vaccine, not a lifetime increased risk that will follow a person long after vaccination.

      Hope that helps!

  5. Measles itself (the disease) can also cause thrombocytopenia. It’s a well-known complication:

    I’ve been unable to find a study comparing the rate of ITP after vaccination to the rate of low platelets after measles disease. That would be an interesting comparison.

  6. I’m curious, have you read anything about a connection between the chickenpox vaccine and increased rate of shingles in people under 50?

    I ask because I was diagnosed with shingles on Monday, and I’m only 35. I’ve stumbled across theories here and there connecting the vaccination to increased shingles cases while researching the disease. I haven’t had the energy to look too deeply into it yet, but I thought your input would be interesting.

    • Tara Haelle

      First, I’m sorry — shingles SUCKS. My husband is exactly your age and just got over shingles a couple weeks ago, and it was horrible. (We also have an infant under 1 year old, so we had to be sure our baby didn’t come into contact with the rash and then develop chickenpox.)

      Your question is a common one, and it’s one that concerned scientists for a while. There was an increase in shingles cases that occurred alongside the introduction of the chickenpox vaccine, and researchers were concerned that there was a link between the two, that lower levels of chickenpox circulating in the environment deprived people of the immune boost they needed to make the antibodies against varicella and thereby reduce their chances of getting shingles. However, after a couple studies, it’s been determined that there’s not evidence to show one caused the other. I briefly discuss this in my post on the chickenpox vaccine here: In that post, I link to one of a couple studies that found the increase in shingles actually preceded the introduction of the chickenpox vaccine: It’s still not clear what’s causing an increase in shingles. More stress? Environmental effects like pollution that reduce the immune system’s function? More old people getting older? It’s something I hope to dig more into after I finish the book, but so far, I haven’t seen anything compelling to explain it. It sucks that people younger than 50 can’t get the shingles vaccine, but even that may not help, as my husband and I found when we looked into it. The vaccine wears off (5 years or so? if I recall correctly?), so you’d need to keep getting a booster. The best you can do is make sure you get on antivirals ASAP and then rest. Afterward, to avoid relapses, keep your immune system strong with healthy diet, exercise, good sleep, low stress, etc.

  7. Amy Hunter

    My daughter is 4 years old never had an allergic reaction to any vaccine she received the MMRV vaccine and within 2 to 3 days she was covered in the worst skin reaction. I took her back to her pediatrician who was blown away with how quickly she showed signs of reaction it was unbearable as a mother to witness my daughter being miserable and in pain. I would love to share photos of the progression of her reaction

    • Tara Haelle

      Yes, allergic reactions are unfortunately a possible risk to vaccines. I hope that she recovered quickly and they were able to identify what caused it. Did she have a similar reaction to the MMR during her first dose? It’s possible that the reaction resulted from the combination of MMR and Varicella in one shot, which is known to have an increased risk of side effects over the MMR and Varicella in separate shots.

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