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NEW ORLEANS -- Everyone who received their second dose of the Moderna or Pfizer mRNA vaccine against COVID-19 at military facilities after experiencing allergic reactions to the first did just fine without any pretreatment, a physician reported here.

These individuals were observed closely, of course, and some underwent allergy testing beforehand to ascertain whether they were genuinely reactive to the vaccines or its components, said Benjamin St. Clair, DO, of Walter Reed National Military Medical Center in Washington, D.C., in a talk at the American College of Allergy, Asthma and Immunology's annual meeting.

A few individuals ultimately were advised not to have the second vaccine dose. But for the majority, physicians determined that the risk was minimal, and none of those accepting the second dose had further problems, St. Clair said.

That is likely to prove significant now that the Biden administration is requiring service members to be vaccinated against COVID-19, he noted -- a total of more than 2.2 million people. Whereas his group found only 23 people experiencing reactions to the first dose through June 15 (the vaccine mandate was implemented in September but hasn't been fully enforced yet), the number will surely increase by orders of magnitude. And even more so if the administration succeeds in its effort to require vaccination for all large civilian employers.

For their study, St. Clair and colleagues searched records of all individuals receiving COVID vaccinations at Walter Reed or the Defense Health Agency's vaccination division. (Not all were necessarily active-duty personnel, he said -- some may have been family members.) The 23 included for analysis were those experiencing reactions classified as either probable or possible anaphylaxis, or having potential "late" allergic reactions occurring more than 24 hours post-jab.

That classification followed standard criteria in which probable anaphylaxis was defined as reactions seen within 4 hours of vaccination that involved at least two of the following organ systems: dermatologic, respiratory, cardiovascular, or gastrointestinal. Possible anaphylaxis was defined as symptoms in just one of those systems within 4 hours, or involving two or more but delayed beyond 4 hours.

Skin testing was performed on some of these individuals as determined by their treating physicians, targeting polyethylene glycol 3350, polysorbate 20, and polysorbate 80, which are included in the mRNA vaccines and are known allergens. Some patients underwent skin testing with actual COVID vaccines taken from expired vials.

Three people had probable anaphylaxis and 12 had possible anaphylaxis after the first dose. Another four had non-urticarial rashes occurring more than 24 hours after dosing; four had mild effects but were referred anyway for evaluation.

The four people having mild effects got their second doses with no problems. Of the four experiencing the non-urticarial rashes, all were offered the second dose, three took it without having reactions, and the fourth decided not to have the second dose.

Among the three with probable anaphylaxis after the first dose, one underwent skin testing and, despite negative results, declined the second dose. The two others didn't have the skin testing; one got the second dose without difficulty, and clinicians decided not to offer it to the other, "as this was early on in our vaccine campaign and we were a little more hesitant to give a second dose in patients with concern for an immediate reaction," St. Clair said.

In the 12 with possible anaphylaxis, four then had skin testing, all negative, and all receiving the second dose without problems. Eight had no skin testing: four got second doses that went smoothly, three were offered but declined, and the last had "an underlying seizure disorder" and clinicians decided not to give the second dose.

Overall, St. Clair said, 15 of the 23 "tolerated the second dose with minimal to no adverse effects." Another five refused the second dose "despite being offered"; and "two patients were advised against" second doses.

St. Clair also reported that two additional individuals had significant reactions after their second dose: one case of probable anaphylaxis and one of acute transverse myelitis that occurred late.

In summary, he said the study dovetailed with others showing that second mRNA vaccine doses could be tolerated in individuals having anaphylactic reactions to the first dose. "This highlights that first-dose anaphylaxis does not always mean they are allergic," nor that one should expect the same reaction with later challenge.

Thus, the vaccines' labels that call to second doses should be reconsidered, St. Clair concluded.

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