What’s in the rsv vaccine
Executive summary
Three distinct RSV vaccines authorized in recent years use different active ingredients: protein-based “prefusion F” antigens in Pfizer’s ABRYSVO and GSK’s AREXVY, and a nucleoside‑modified mRNA encoding the prefusion F protein in Moderna’s MRESVIA; formulations also include adjuvants (in AREXVY), lipid nanoparticles (in MRESVIA), and standard buffer/stabilizer excipients such as sucrose and tromethamine [1] [2] [3]. Exact ingredient lists differ by product and indication—pregnancy use is currently limited to Pfizer’s ABRYSVO—so which vaccine someone receives determines what’s “in” an RSV dose [4] [5].
1. Active ingredients: prefusion F proteins vs. mRNA
Pfizer’s ABRYSVO contains recombinant prefusion-stabilized F proteins from both RSV‑A and RSV‑B (120 µg total: 60 µg each) as the antigenic active ingredient [2] [4], GSK’s AREXVY uses a recombinant RSV F protein antigen stabilized in the prefusion conformation (preF) as its active antigen [1] [6], and Moderna’s MRESVIA delivers 50 µg of nucleoside‑modified mRNA encoding the RSV F glycoprotein (preF) rather than a protein antigen [1] [3].
2. Adjuvants and why they matter
AREXVY is adjuvanted with GSK’s AS01E system (the same adjuvant family used in Shingrix though at a lower dose), which contains immune‑stimulating components designed to boost antibody responses to the protein antigen [1] [7]; ABRYSVO, by contrast, is not adjuvanted for its maternal indication and is supplied as a lyophilized antigen reconstituted with diluent [4] [2]. The presence or absence of an adjuvant affects reactogenicity and the immune profile targeted by the vaccine [1] [7].
3. Lipids, PEG and the mRNA platform (MRESVIA)
Moderna’s MRESVIA uses a lipid nanoparticle (LNP) formulation to deliver the mRNA and lists a total lipid content including proprietary ionizable lipids (e.g., SM‑102 analogues), PEG‑containing lipids (PEG2000‑DMG), cholesterol and phospholipids (DSPC), which are typical of mRNA vaccines and encapsulate and protect the mRNA for cell uptake [3]. MRESVIA’s dose also includes buffer components (tromethamine/tromethamine hydrochloride), acetate, sucrose and water for injection as excipients [3].
4. Buffering agents, stabilizers and trace byproducts that show up on labels
Across the products, excipients listed in regulatory and manufacturer materials include tromethamine/tromethamine hydrochloride (buffers), sucrose and mannitol (stabilizers/lyoprotectants), polysorbate 80 (surfactant), sodium chloride, and small quantities of acids/acetates in mRNA formulations [2] [3] [8]. Package inserts and safety summaries also note potential residuals from manufacturing—such as trace proteins or DNA from cell substrates used to produce recombinant proteins (e.g., Chinese hamster ovary cell byproducts)—which are quantified, controlled and disclosed in product information [8] [2].
5. Safety context, regulatory notes and limits of available reporting
Regulatory documents and CDC guidance emphasize that these ingredients are present at small, controlled amounts and that product labeling includes known adverse events and warnings—Pfizer’s ABRYSVO insert, for example, lists specific buffer quantities per 0.5 mL dose and notes post‑marketing observations such as a possible increased risk signal for Guillain‑Barré syndrome that is under study [2] [9]. Public materials also clarify which vaccines are approved for which populations (ABRYSVO for maternal use to protect infants; AREXVY and MRESVIA for older adults) and advise consulting package inserts for complete composition and handling details [4] [1]. The reporting compiled here is limited to the cited regulatory and institutional sources; if a precise manufacturing impurity level or proprietary lipid chemical name beyond public documents is desired, those details are not contained in the provided material and would require consulting full FDA/EMA dossiers or manufacturer technical data [3] [6].