IFNG and COVID-19: Alhydrogel is a wet gel suspension of aluminum oxyhydroxide that is the most commonly used human adjuvant (32, 33) and was included because a recent COVID-19 vaccine study using an alum-stabilized Pickering emulsion (PAPE) showed enhancement of RBD-specific IgG1 and IgG2a and IFN-γ-secreting T cells (31).