Anaphylaxis

In the revised EUA issued for its COVID vaccine on February 25, 2021, the FDA required Pfizer to updated its “Fact Sheet for Healthcare Providers” to include post-authorization adverse effects. As a result, Pfizer’s fact sheet now states, “Severe allergic reactions, including anaphylaxis [emphasis added], and other hypersensitivity reactions (e.g., rash, pruritus, urticaria, angioedema) have been reported following administration of the Pfizer-BioNTech COVID-19 Vaccine during mass vaccination outside of clinical trials.”  Moderna did not receive the same mandate to revise its fact sheet, which still does not include a similar warning about anaphylaxis.  What is anaphylaxis and what are the facts about this life-threatening vaccination complication?

Anaphylaxis is a severe allergic reaction in which your body releases a flood of chemicals designed to modulate the immune response all at once.  The result is a sudden drop in blood pressure and narrowing of airways which can lead to fainting and death.  Some people are more prone to anaphylaxis than others, and some stimuli are more common causes of anaphylaxis than others.  Peanuts and bee stings are common examples.  The allergic response can be effectively reversed by an injection of epinephrine.  Susceptible individuals (and you know who you are) often carry EpiPens to self-administer a dose of epinephrine in case of a reaction.

Anaphylaxis can occur anytime something is injected in the body, although the risk is exceedingly low.  However, the rate of anaphylaxis after the mRNA vaccines is about ten times higher than the rate of pre-COVID vaccines.  If this is the case, then why did Pfizer’s new EUA highlight this potential complication and Moderna’s did not?  The answer may be related to initial experience with the two vaccines.  Since Pfizer received authorization for its vaccine first, increased anaphylaxishad already been observed in association with the Pfizer vaccine before Moderna even received its EUA.  The reputation stuck.  Although initial reports suggested that Pfizer caused more than twice as many anaphylaxis reactions as Moderna, subsequent experience has shown that both mRNA vaccines have about the same rate of anaphylaxis.  According to a March 16 CDC report 1,913 deaths have been reported associated with vaccine administration after more than 109 million doses.  Reports of recent VAERS data searches, the FDA database collecting vaccine adverse events, suggest that the rate of anaphylaxis deaths are similar for the two vaccine manufacturers.  The Janssen recombinant vector vaccine appears to be associated with fewer cases of anaphylaxis than the mRNA vaccines; time will tell whether this observation sticks or is skewed by the fewer number of vaccines administered so far.  The CDC recommends that all vaccination administration sites be prepared for potential anaphylaxis reactions, including educating staff on the signs and symptoms of anaphylaxis and having at least three epinephrine doses on hand at all times.

A few sensible conclusions may be drawn from this information.  

• Ask the person administering your vaccine what would happen if you had an anaphylaxis response.
• If you have an EpiPen, bring it with you when you get your vaccine.
• If you have had a severe allergic reaction in the past, consider deferring vaccination or taking the Janssen (Johnson and Johnson) vaccine instead of an mRNA vaccine.