Thread by @KimberlyBlumen1

1/ OK so 1 week after UK #COVID19Vaccine allergy was described, I need to reorient you to my world, the world where #drugallergy is the best field of #MedTwitter #AIMedEd #allergyimmunologyrocks. Let's get down to this confusion about the #covid19vaccine and #allergy

2/ There is no reason to think that anyone -- other than patients with a known allergy to an ingredient in this vaccine or an ingredient cross-reactive to an ingredient in this vaccine -- might have an #allergy the @pfizer #CovidVaccine.

3/ There is even very little that we think could cause an #allergy in this @pfizer vaccine. But 2 patients had #anaphylaxis after vaccination and we need to think about why. Something epidemiologically different in the UK population compared to clinical trial populations?

4/This vaccine has Polyethylene Glycol (PEG) conjugated to a lipid but this is a new PEG and no one therefore has ever had a case of allergy to this specific PEG. PEG allergy is rare; world experts @vumc_cdsi_rsch @lenehgarvey can count the cases they've seen. I have seen ONE.

5/ It is easy to confirm you are not allergic to PEG because PEG is everywhere, in products in the pharmacy and more than 1K @US_FDA medications. PEG is Golytely, Miralax, PEGylated medications, ultrasound gel, and injectable steroids.

6/ PEGs can be cross-reactive with each other and polysorbates (another macrogal). PEGs are not in any prior vaccines, but polysorbates are in many existing vaccines: e.g., Tdap, Influenza, Zoster, HPV, HBV, HAV. The main #CovidVaccine candidates have either PEG or polysorbate.

7/ So, guidance is unclear because regulatory agencies from different countries are not proposing the same thing! For the US, defer vaccine for now ONLY if there is a severe allergy history to a PEG or your first #COVIDvaccine dose.

8/Patients with severe allergy to another vaccine or injectable medication should wait 30 minutes after vaccination. The idea is that prior vaccines/injectables could have PEG or polysorbate and no one would know what specifically they are allergic to.

9/This guidance is risk averse and is expected to change as we gain more experience. This experience may come even before widespread vaccination as we see outcomes from healthcare workers vaccinated in the coming weeks @CDCgov #RightToBareArms

10/ All people with food allergy, latex allergy, seasonal allergies, eczema, or allergy to oral medications should proceed with usual vaccination. If you want to discuss your allergy history with an allergist prior to vaccination, find an allergist: allergist.aaaai.org/find/

11/ #medtwitter if you need an #allergist to come explain this in a grand rounds or a webinar, reach out! I suggest: @rebeccasaff @AnnaBanana528 @PaigeWickner !/end

@drjessigold @TrubianoJason @JonnyPeter7 @AleenaBanerjiMD @mgh_id @MGHAllergy @mghaifellows @mghmedres @MonganInstitute @MGH_ClinEpi @USdrugallergy @TaisonBell @IDDoc1978 @ARLetourneau @ericashenoy