How Often Do Severe Events Occur After Vaccines?

Most of us understand that vaccine reactions are usually mild. While severe events can occur after vaccines, they are very rare.

“That measles infections can cause neurologic side effects on rare occasions is known, but the complication rate for vaccinations is low. After infectious measles encephalitis, risk of an autistic regression has occurred in 1/1000 to 1/10,000 cases. If the trend toward delaying vaccination continues because parents remain misinformed about the MMR, the number of children with neurologic complications of measles or rubella will increase. ”

Chez et al on Immunizations, Immunology, and Autism

Unfortunately, being worried about severe reactions sometimes scares parents away from vaccinating and protecting their kids.

How Often Do Severe Events Occur After Vaccines?

Hopefully, realizing just how rare these severe reactions are will help more parents understand that all of the benefits of vaccines (very big) truly do outweigh the risks (very small).

How often do severe events occur after MMR vaccines?
How often do severe events occur after MMR vaccines?

So how often do these events occur?

Are there any statistics?

Using the MMR vaccine information statement as an example, we see that it lists the following severe events:

  • deafness – which is so rare to be associated with MMR that it is hard to tell whether they are caused by the vaccine
  • long-term seizures, coma, or lowered consciousness – which is so rare to be associated with MMR that it is hard to tell whether they are caused by the vaccine
  • brain damage – which is so rare to be associated with MMR that it is hard to tell whether they are caused by the vaccine
  • severe allergic reaction – which occurs in less than 1 out of a million doses
  • serious injury or death – which is so rare to be associated with MMR that it is hard to tell whether they are caused by the vaccine

Wait.

Why can’t we tell if these problems are caused by the vaccine?

In some cases, the association is based on a few case reports.

“With respect to the recent claims of deaths caused by MMR vaccine, drawing broad cause and effect conclusions between vaccination and deaths based on spontaneous reports to VAERS, some of which might be anecdotal or second hand, is not a scientifically valid practice. In fact, a review of the VAERS data reveals that many of the death reports for MMR vaccine involved children with serious preexisting medical conditions or were likely unrelated to vaccination (e.g., accidents). These complete VAERS reports and any accompanying medical records, autopsy reports and death certificates have been reviewed in depth by FDA and CDC physicians and no concerning patterns have emerged that would suggest a causal relationship with the MMR vaccine and death.”

Miller et al on Deaths following vaccination: What does the evidence show?

Mostly though, these type of severe events just occur so rarely after getting vaccinated.

“As for vaccines causing death, again so few deaths can plausibly be attributed to vaccines that it is hard to assess the risk statistically.”

WHO on Six common misconceptions about immunization

At a rate of less than 1 in a million doses, it gets hard to know if something was really caused by the vaccine or if it was just a coincidence, as you don’t have a lot of cases to compare with each other.

Still, it should be reassuring that even if they were caused by the vaccine, these serious events are extremely rare.

Vaccines are safe, with few risks.

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