Q: Is the PEG you test for the same as what’s in the Pfizer and Moderna vaccines?

A: Both the Pfizer and Moderna vaccines use PEG 2000. We have added PEG 4000 as an LRA test item. PEG2000 and PEG 4000 differ in size but not antigenicity / reactivity. If someone is reactive to PEG 4000 they should assume they would also be reactive to PEG 2000.


Q: How is the Polyethylene Glycol on your FAP 45 panel different from the PEG-2000 in the vaccines?

A: We test for both low molecular weight (PEG) and high molecular weight PEG 4000 as well as polysorbate 80.


Q: What is the difference between PEG-2000 and PEG-4000?

A: The only difference is a small average size difference. PEG2000 and PEG 4000 differ in size but not antigenicity / reactivity.


Q: Why don’t you test for PEG-2000?

A: PEG 4000 and PEG 2000 are completely cross-reactive. If one reacts to PEG 4000 on the LRA it should be assumed they would also react to the PEG 2000 in the vaccines.


Q: Is Polysorbate 80 in the Pfizer, Moderna, and J & J vaccines?

The J & J vaccine uses Polysorbate 80 in place of PEG 2000


Q: What is the difference between Polysorbate 20, 60, and 80 and are they all cross-reactive?

A: The active element in all of them is polysorbate. The only difference is which fatty acid is used, which makes them better suited for different applications.  Whatever the counter ion, the active element is polysorbate.

  • Polysorbate 80 uses oleic acid
  • Polysorbate 60 uses stearic acid
  • Polysorbate 20 uses lauric acid


Q: I understand the LRA test identifies delayed hypersensitivities. The reported PEG 2000 reactions have been immediate. If I am not reactive on your test, does that mean I won’t have an immediate reaction either?

A: There are multiple pathways involved in the PEG 2000 reactions that have been seen so far. More importantly, the longer-term implications of the vaccine have not yet been studied but will likely be associated with the delayed immune hypersensitivity pathways. If you have or suspect you’ve had an immediate reaction to PEG or polysorbate in the past your physician can confirm the sensitivity with a skin test. Generally, if you have had any hypersensitivity to PEG, polysorbate, or any other ingredient in a vaccine, it is recommended that you do not get the vaccine. Immediate reactions overlap with delayed reactions.

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