Side Effects and Adverse Events Following Immunizations

Vaccines are safe, but they do have some side effects, mostly mild, and they rarely cause some serious and severe adverse reactions.

Vaccine adverse events can be reported to VAERS online or using a downloadable form.
Vaccine adverse events can be reported to VAERS online or using a downloadable form.

To help keep our vaccines safe, it is important that all “clinically important adverse events that occur after vaccination of adults and children” be reported to VAERS, not just the ones that are known to be side effects.

Wait.

Isn’t an adverse event the same as a side effect?

Adverse Events Following Immunizations

To better understand that, let’s first look at how we define an adverse event following immunization (AEFI):

“An Adverse event following immunization (AEFI) is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. The adverse event may be any unfavourable or unintended sign, abnormal laboratory finding, symptom or disease.”

Classification of AEFIs

So it should be clear that not all adverse events are actually caused by vaccines.

Many are coincidental events that simply occur after a vaccine is given.

What’s the Difference Between Side Effects and Adverse Events Following Immunizations?

Others are true vaccine reactions though, including fever, pain, fainting, and allergic reactions, etc.

“A side effect is any health problem shown by studies to be caused by a vaccine. Like any medication, vaccines can cause side effects. Usually vaccine side effects are minor (for example, a sore arm where a shot was given or a low-grade fever after a vaccine) and go away on their own within a few days.”

Understanding Side Effects and Adverse Events

These are the reactions that we call side effects or adverse reactions of the vaccine.

Still, just because a sign or symptom can be a side effect of a vaccine doesn’t mean that it always will be.

“A vaccine reaction is an individual’s response to the inherent properties of the vaccine, even when the vaccine has been prepared, handled and administered correctly.”

Vaccine reactions – WHO Vaccine Safety Basics

Here are some other definitions:

  • adverse event – Medical occurrence temporally associated with the use of a medicinal product, but not necessarily causally related.
  • adverse reaction/side effect – A response to a drug which is noxious and unintended, and which occurs at doses normally used in man for the prophylaxis, diagnosis, or therapy of disease, or for the modifications of physiological function.
  • unexpected adverse reaction – Not consistent with applicable product information or characteristics of drug.
  • severe adverse event or reaction – are rarely life-threatening and usually do not result in long-term problems
  • serious adverse event or reaction – Any untoward medical occurrence that at any dose is life-threatening, results in death, requires inpatient hospitalization or prolongation of existing hospitalization, or results in persistent of significant disability or incapacity

Does understanding those definitions make it easier to see why you should be skeptical when folks try to scare you with VAERS reports and data from package inserts?

“Reports of all possible associations between vaccines and adverse events (possible side effects) are filed in VAERS. Therefore, VAERS collects data on any adverse event following vaccination, be it coincidental or truly caused by a vaccine. The report of an adverse event to VAERS is not documentation that a vaccine caused the event.”

Guide to Interpreting VAERS Data

They both can include reports about adverse events, not just side effects. So they both include events that can very well be coincidental, and not caused by a vaccine.

So when doing your research about vaccines, focus on real side effects, or things that are known to be caused by vaccines. You will find that most vaccine side effects are mild and that more serious or severe side effects are very rare.

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