From: https://www.fda.gov/media/150386/download https://www.fda.gov/media/150386/download "The two formulations of the Pfizer-BioNTech COVID-19 Vaccine and COM

From: https://www.fda.gov/media/150386/download https://www.fda.gov/media/150386/download "The two formulations of the Pfizer-BioNTech COVID-19 Vaccine and COMIRNATY (COVID-19 Vaccine, mRNA) differ with respect to certain inactive ingredients only and have been shown to be analytically comparable.35 35 Analytical comparability assessments use laboratory testing to demonstrate that a change in product formulation does not impact a product's safety or effectiveness. For the Pfizer-BioNTech COVID-19 Vaccine, multiple different release parameters were evaluated to assess the comparability of the modified formulation (the formulation with the Tris buffer) to the originally-authorized formulation (the formulation with the PBS buffer). These release parameters ranged from product appearance to size of the lipid-nanoparticle to the integrity of the modRNA in the product. Release and characterization tests include tests for purity, composition, and critical attributes of mRNA associated with the activity of the vaccine. The combination of release testing and characterization testing demonstrated that the modified formulation is analytically comparable to the original formulation." Changing one buffer to another (to keep the vaccine at a similar pH to the body) isn't likely to have any active effect.