Rash After the MMR

It is not uncommon to get a rash after your child gets their MMR vaccine.

In fact, about 1 in 20 people get a rash after their first dose of MMR.

It typically shows up about 6 to 14 days after the dose.

Fortunately, it doesn’t mean that your child has full-blown measles as some people suspect.

So why do some kids get a rash after their MMR?

It depends on which rash they have.

While there is one classic MMR rash that we think about, there are actually a few other rashes that can occur even more rarely, including:

hives – an allergic reaction to the vaccine or one of it’s components
petechia and/or purpura – caused by temporary thrombocytopenia (low platelet count) in about one out of every 30,000 to 40,000 doses of vaccine given

And then there is the rash that up to 5% or people get about 7 to 10 days after their dose of MMR – a mild vaccine reaction that goes away on its own without treatment.

Most importantly, the presence of this measles-like rash does not mean that your child has actually gotten measles from the vaccine.

How do we know?

For one thing, the MMR vaccine is made with an attenuated or weakened form of the measles virus, so it can’t actually cause full-blown measles, unless maybe a child has a severe immune system problem.

Also, there is no viremia after vaccination.

“There are no reports of isolation of vaccine virus from blood in normal humans.”

Plotkin’s Vaccines

It is also important to note that “person-to-person transmission of vaccine virus has never been documented.”

And kids who get a rash after their MMR vaccine are not considered to be contagious. At most, you would expect them to shed the weakened vaccine virus, but they don’t.

What’s causing this measles-like rash then?

Like the fever, it is thought to be a delayed immune response to the live, attenuated virus in the vaccine.

When the Rash Really is Measles

Are there any situations in which a child gets a rash after their MMR vaccine and it could really be measles?

Sure.

An infant hospitalized during a measles outbreak in the Philippines in which 110 people died. — An infant with wild type measles hospitalized during a measles outbreak in the Philippines in which 110 people died. Photo by Jim Goodson, M.P.H.

Your child could have been exposed to wild type measles right around the time they got vaccinated, and then went on to develop regular measles.

While getting a measles vaccine within 72 hours of exposure (post-exposure prophylaxis) can reduce your chance of getting measles, it isn’t a perfect strategy.

Or your child could have been vaccinated and been one of the few people for whom the vaccine failed to work. So their rash, again, would be from a wild type strain of measles that they were exposed to and not from the shot.

Can you tell the difference if someone has measles from the vaccine or from a wild type strain?

Sure.

“During outbreaks, measles vaccine is administered to help control the outbreak, and in these situations, vaccine reactions may be mistakenly classified as measles cases.”

CDC on Genetic Analysis of Measles Viruses

You just have to test the measles strain to see if it is the wild type virus or a vaccine strain.

Does It Matter If It Is the MMR Vaccine or Measles?

About now, you are probably wondering why it matters knowing if a child’s rash is caused by measles or the MMR vaccine, right?

For one thing, if a parent thinks a vaccine gave their child measles, then they might not want to get vaccinated again. They will especially think twice about getting another MMR.

Also, if a child really does have full-blown, wild type measles and you simply blame their MMR vaccine, then you might miss someone else in the community that exposed the child to measles. And that’s why some outbreaks are hard to stop.

Lastly, if you simply blame the vaccine, you might miss something else that is causing the child to be sick.

Need an example?

During the 2010 measles outbreaks in Canada, a 15-month-old develop a rash, fever, and other symptoms 12 days after getting their MMR vaccine. Did the have measles, a vaccine reaction, or something else?

Turns out that he had scarlet fever.

The child tested positive for Streptococcus pyogenes (group A streptococcus), the bacteria that causes strep throat and scarlet fever. He also tested positive for vaccine strain measles. He did not have the wild strain of measles, and in fact, did not have measles at all.

Again, he had scarlet fever and it was just a coincidence that he had recently received an MMR vaccine.

But isn’t there another case report from Canada that does prove that you can get full-blown measles from the MMR vaccine? While there is such a case report, it is hardly proof of anything.

“It is possible that the case’s symptoms were not measles-vaccine-related but an inter-current illness confounding the presentation.”

Murti et al on Case of vaccine-associated measles five weeks post-immunisation, British Columbia, Canada, October 2013

The problem with the case?

For one thing, the child already had high levels of IgG antibodies at the time he had the rash, which developed 37 days after he got his vaccine.

“The two-fold rise between acute and convalescent measles-specific IgG suggests the vaccine-mediated immune response had been underway prior to the onset of symptoms.”

Murti et al on Case of vaccine-associated measles five weeks post-immunisation, British Columbia, Canada, October 2013

This was neither a typical reaction nor a typical case. And it very well might not have been measles. If it was, it was a very rare exception to the rule that rashes after the MMR vaccine aren’t full-blown measles.

What to Know About Rashes After the MMR Vaccine

The rash that your child can get after their MMR vaccine is not a sign that they have developed full-blown measles, instead, it is a mild vaccine reaction that will quickly go away without any treatment.

Rash After the MMR – Is This Normal?