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What Are Hypotonic-Hyporesponsive Episodes?

Just about any side effect after a vaccine can be scary for parents.

What if your child suddenly became limp, wasn’t responsive, and was pale?

That would be scary for any parent.

What Are Hypotonic-Hyporesponsive Episodes?

But that’s just what can happen when a child has a hypotonic–hyporesponsive episode (HHE).

“A hypotonic-hyporesponsive episode (HHE) is the sudden onset of hypotonia, hyporesponsiveness, and pallor or cyanosis that occurs within 48 hours after childhood immunizations.”

DuVernoy et al on Hypotonic-hyporesponsive episodes reported to the Vaccine Adverse Event Reporting System (VAERS), 1996-1998

These types of episodes were once thought to happen once for every 1,750 DTP vaccines given.

HHE is much more rare since we switched to a new pertussis vaccine.
HHE is much rarer since we switched to a new pertussis vaccine.

Fortunately, although they certainly do sound scary, the episodes stop on their own and  don’t cause any permanent harm.

Hypotonic-hyporesponsive episodes were even removed as table injuries after DTP back in 1995. It is not that HHE can’t occur after DTP, DTaP, or other vaccines, but rather that HHE doesn’t then cause any permanent neurological damage to the child.

And it is rare for kids to have a second episode, so they can continue to get vaccinated. HHE is not a good reason to skip or delay all of your child’s vaccines. While not a contraindication to getting vaccinated, having an episode of HHE “within 48 hours after receiving a previous dose of DTP/DTaP,” is listed as a precaution to getting another dose of DTaP or Tdap though.

“In general, vaccinations should be deferred when a precaution is present. However, a vaccination might be indicated in the presence of a precaution if the benefit of protection from the vaccine outweighs the risk for an adverse reaction.”

CDC on Vaccine Contraindications and Precautions

Also, HHE has become even more rare since we switched to using DTaP, instead of the older DTP vaccine. So being worried about HHE is definitely not a good reason to skip or delay any vaccines.

What to Know About Hypotonic-Hyporesponsive Episodes

Hypotonic-hyporesponsive episodes were more common after the older DTP vaccines, but still didn’t cause any long term problems and aren’t a good reason to skip or delay your child’s vaccines.

More About Hypotonic-Hyporesponsive Episodes

3 thoughts on “What Are Hypotonic-Hyporesponsive Episodes?”

  1. Also, HHE has become even more rare since we switched to using DTaP, instead of the older DTP vaccine. So being worried about HHE is definitely not a good reason to skip or delay any vaccines.

    Oh, that’s OK, then. Just forget about the thousands of children and families around the world that you killed, “developmentally delayed” permanently, and, in general, destroyed.

  2. All studies on hypotonic-hyporesponsive vaccine effects are children related. After having the prevnar 13 vaccination one morning years ago I had a hypotonic-hyporesponsive event in the middle of the night. I felt extremely hot throughout my entire body and could not move or speak. This event debilitated for about 2 months. I had no energy due to entire body weakness. I informed 2 physicians and was told by one it was a coincidence and was totally ignored by the second doctor. Now the covid-19 is upcoming and I am scared. Perhaps if my event was aknowledged I would lose that fear of the vaccination. Where can those of us who have had such an experience find information about such events. I was approximately 69/70 years old then and am almost 74 now. I am sure that other adults have had such an event

    1. Yes, I have had such an event. I had the same experience as you, in the middle of the night following the 2nd dose of the shingles vaccine that afternoon. It lasted 30 minutes, with no long term effects.

      I have now had the first dose of the Moderna’s covid vaccine in the afternoon and had a similar experience in the middle of the night. This time it was milder, with only my arms being weak and lasting only 10 minutes. I am afraid of getting the second dose.

      I am also looking for more information about this in adults.

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