Immunogenicity and non-inferiority evaluation of dose-sparing adjuvanted inactivated polio vaccine in Wistar rats.

Global efforts toward poliovirus eradication have prompted a shift from oral polio vaccine (OPV) to inactivated polio vaccine (IPV), particularly in low-resource settings. However, limited IPV supply and high production costs pose challenges to widespread implementation. Antigen-sparing strategies, including the use of aluminum-based adjuvants, offer a promising solution to increase IPV accessibility without compromising immunogenicity. In this study, monovalent and trivalent reduced-dose IPV formulations adjuvanted with aluminum hydroxide were evaluated for immunogenicity in Wistar rats. Groups of rats (n = 10/group) were intramuscularly immunized with various D-antigen units (DU) of adjuvanted Salk IPV types 1, 2, and 3. Neutralizing antibody responses were measured using a standardized serum neutralization test (SNT), and results were compared to those of a non-adjuvanted commercial trivalent IPV (T1: 40 DU, T2: 8 DU, T3: 32 DU). Adjuvanted monovalent formulations elicited comparable or superior neutralizing titers relative to the control vaccine, despite containing significantly lower antigen doses. For instance, adjuvanted T1 at 10 DU achieved titers comparable to the 40 DU control, while T2 at 8 DU induced significantly higher responses than the control (p ≤ 0.01). Adjuvanted T3 at 2.5 and 5 DU showed comparable responses, and at 10 DU produced significantly higher titers than the control (p ≤ 0.05). These results support the feasibility of dose reduction through adjuvantation without compromising vaccine potency. The IPV formulations exhibited strong stability and potency under recommended storage conditions, supporting their suitability for long-term use. The study demonstrates that aluminum-adjuvanted reduced-dose IPV formulations can achieve immunogenicity comparable to or exceeding that of standard-dose commercial IPV. This antigen-sparing approach could play a vital role in enhancing global IPV supply and supporting polio eradication strategies.