Also known as: AAHS, aluminum hydroxyphosphate sulfate, amorphous aluminum hydroxyphosphate sulfate
Amorphous Aluminum Hydroxyphosphate Sulfate (AAHS)
Sourced from FDA-approved package inserts (DailyMed). Last verified: 2026-07-09.
What It Is & Why It's in Vaccines
Amorphous aluminum hydroxyphosphate sulfate (AAHS) is a proprietary aluminum salt adjuvant used in several Merck vaccines. It is chemically distinct from both aluminum hydroxide and aluminum phosphate, with intermediate surface properties that affect antigen adsorption.
Same general adjuvant role as other aluminum salts — prolongs antigen presentation and enhances humoral responses. Products that use AAHS include Gardasil 9, Recombivax HB, Vaqta, and PedvaxHIB (see product composition records for per-dose aluminum content).
Dose-in-Context
Per-Dose Quantity
Typically ~0.225–0.5 mg elemental aluminum per dose depending on product (e.g., Gardasil 9 ≈0.5 mg Al; Vaqta pediatric ≈0.225 mg Al).
Reference Comparison
Subject to the same FDA aluminum limits (21 CFR 610.15) and the same pharmacokinetic framework as other injectable aluminum adjuvants (Mitkus et al. 2011).
Source: Mitkus RJ et al. Vaccine. 2011;29(51):9538-9543.
Route-of-Administration Note
Injected aluminum; oral dietary aluminum reference values are not directly transferable without PK adjustment.
Documented Adverse Effects
Local injection-site reactions (pain, swelling, erythema) more common with aluminum-adjuvanted vaccines.
No causal association established between aluminum adjuvants including AAHS and neurodevelopmental disorders in large epidemiological reviews.
Vaccines Containing Amorphous Aluminum Hydroxyphosphate Sulfate (AAHS)
Hepatitis B — Recombivax HB (Merck Sharp & Dohme LLC)
Aluminum salt is AAHS (chemically distinct from aluminum hydroxide used in Engerix-B).
HPV — Gardasil 9 (Merck Sharp & Dohme LLC)
Hib — PedvaxHIB (Merck Sharp & Dohme LLC)
Hepatitis A — Vaqta (Merck Sharp & Dohme LLC)
ⓘ Methodology Disclaimer: Ingredient lists are sourced from official FDA-approved package inserts for the specific branded products named on each vaccine page. Formulations can change between manufacturing lots and over time — always verify against the current package insert before making a clinical decision. The presence of a substance in a vaccine does not by itself indicate harm; toxicology is dose-, route-, and context-dependent. Comparisons to reference exposure levels are provided with their sources where available, and are approximate — see the cited source for full methodology.