What are the functions of each ingredient in the Pfizer-BioNTech (Comirnaty) vaccine?

1. What the sources say about where ingredient lists live — regulatory and product documents

U.S. CDC interim clinical guidance points readers to COVID-19 vaccine–specific package inserts and U.S. COVID-19 Vaccine Product Information for a full list of ingredients and storage/handling details, indicating that those documents are the primary source for ingredient-level functions; the searchable results provided here quote that guidance but do not reproduce the ingredient lists themselves ^[1]. Pfizer’s press releases and BioNTech investor materials emphasize clinical data and efficacy updates (for example, a 2025 press release on new adapted formulas) but focus on immune response and regulatory outcomes rather than enumerating ingredient functions ^{[2] [3]}.

2. Why journalists and clinicians point to package inserts for “functions of ingredients”

Regulatory package inserts include both the list of components and the roles they play — for instance, which component is the active mRNA and which are excipients (stabilizers, lipids, buffers, salts, sugar) — and CDC guidance explicitly tells clinicians to consult those documents for a “full list of ingredients and information on the conditions of use, storage and” handling ^[1]. The documents cited in the search results establish that ingredient‑level information is not typically summarized in high‑level programmatic guidance but is centralized in manufacturer package inserts and product information ^[1].

3. What the companies report instead: focus on mRNA and immune response

Pfizer and BioNTech communications in these search results concentrate on the vaccine’s active component — the mRNA encoding SARS‑CoV‑2 spike antigen — and on clinical/immunogenicity endpoints. For example, Pfizer’s 2025 press release on an LP.8.1‑adapted formulation reports at least a fourfold neutralizing antibody rise in trial cohorts and frames results in regulatory submission terms rather than ingredient mechanics ^[2]. BioNTech investor and press materials likewise highlight R&D, manufacturing capacity and clinical pipelines without breaking down excipient function by name in the excerpts provided ^{[3] [4]}.

4. What is not in the provided reporting — and why that matters

The provided set does not include the COMIRNATY package insert, FDA fact sheets, or CDC vaccine product labels that explicitly list each ingredient and often summarize the role of excipients (available sources do not mention the actual ingredient list or per‑ingredient functions) ^[1]. Because the most authoritative, ingredient‑level, function‑by‑function descriptions live in those omitted regulatory documents, any attempt here to attribute specific functions to named excipients would be extrapolation beyond the supplied materials (not found in current reporting).

5. Competing perspectives and practical next steps for readers

Public health agencies presented here (CDC) and manufacturers (Pfizer/BioNTech) agree on where to find ingredient detail: consult package inserts and product information for the vaccine formulation and handling instructions ^{[1] [2]}. Independent media and clinical summaries often rephrase that content for lay readers, but those are not among the current search results. To get precise functions (for example, which lipid forms the nanoparticle, which salts buffer pH, which sugar stabilizes during freezing), request or open the active COMIRNATY package insert, FDA-approved prescribing information, or CDC U.S. vaccine product information — documents explicitly referenced by the CDC and manufacturers ^{[1] [2]}.

Limitations: my account strictly follows the material returned in your search results. The detailed ingredient list and per‑ingredient functional descriptions are not present in those items, so I cite only what the available reporting references and recommend the primary regulatory/product documents they themselves direct clinicians and the public to consult ^{[1] [2]}.