(1) Background: The global coronavirus disease 2019 vaccination adapts to protect populations from emerging variants. This communication presents interim findings from the new Omicron XBB.1.16-adapted PHH-1V81 protein-based vaccine compared to an XBB.1.5-adapted mRNA vaccine against various acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strains. (2) Methods: In a Phase IIb/III pivotal trial, adults previously vaccinated with a primary scheme and at least one booster dose of an EU-approved mRNA vaccine randomly received either the PHH-1V81 or BNT162b2 XBB.1.5 vaccine booster as a single dose. The primary efficacy endpoint assessed neutralization titers against the Omicron XBB.1.16 variant at day 14. Secondary endpoints evaluated neutralization titers and cellular immunity against different variants. Safety endpoints comprised solicited reactions up to day 7 post-vaccination and serious adverse events until the cut-off date of the interim analysis. Changes in humoral responses were assessed by pseudovirion-based or virus neutralization assays. (3) Results: At the cut-off date, immunogenicity assessments included 599 participants. Both boosters elicited neutralizing antibodies against XBB.1.16, XBB.1.5, and JN.1, with PHH-1V81 inducing a higher response for all variants. The PHH-1V8 booster triggers a superior neutralizing antibody response against XBB variants compared to the mRNA vaccine. A subgroup analysis consistently revealed higher neutralizing antibody responses with PHH-1V81 across age groups, SARS-CoV-2 infection history, and the number of prior vaccination shots. A safety analysis (n = 607) at the day 14 visit revealed favorable safety profiles without any serious vaccine-related adverse events. (4) Conclusions: PHH-1V81 demonstrates superiority on humoral immunogenicity compared to the mRNA vaccine against XBB variants and non-inferiority against JN.1 with a favorable safety profile and lower reactogenicity, confirming its potential as a vaccine candidate.

In this phase III, open label, single arm, multicenter clinical study, we report safety, tolerability and immunogenicity of PHH-1V as a booster dose in subjects primary vaccinated against COVID-19 with the BNT162b2, mRNA-1273, ChAdOx1-S, or Ad26.COV2.S vaccines, with or without previous COVID-19 infection. A total of 2661 subjects were included in this study and vaccinated with the PHH-1V vaccine. Most treatment-emergent adverse events (TEAE) were solicited local and systemic reactions with grade 1 (58.70%) or grade 2 (27.58%) intensity, being the most frequently reported injection site pain (82.83%), fatigue (31.72%) and headache (31.23%). Additionally, immunogenicity was assessed at Baseline and Days 14, 91, 182 and 365 in a subset of 235 subjects primary vaccinated. On Day 14, geometric mean triter (GMT) in neutralizing antibody against SARS-CoV-2 Wuhan and Beta, Delta and Omicron BA.1 variants increased in all primary vaccination with a geometric mean fold raise (GMFR) of 6.90 (95% CI 4.96-9.58), 12.27 (95% CI 8.52-17.67), 7.24 (95% CI 5.06-10.37) and 17.51 (95% CI 12.28-24.97), respectively. Despite GMT decay after day 14, it remains in all cases significatively higher from baseline up to 1 year after PHH-1V booster administration and GMFR against Beta and Omicron BA.1 variants over 3 at 1 year after booster compared to baseline. PHH-1V booster vaccination elicited also a significant RBD/Spike-specific IFN-γ ⁺ T-cell responses on Day 14. Overall, PHH-1V vaccine was immunogenic and well-tolerated regardless of the previous primary vaccination scheme received with no reported cases of severe COVID-19 infection throughout the entire study.

SARS-CoV-2 vaccination campaigns on current endemic situation would benefit from vaccine alternatives with easy logistics and accessibility, sustained response and cross-reactivity against emerging variants. Herein, safety and immunogenicity of PHH-1V, adjuvanted recombinant RBD-based vaccine, as fourth dose for the most prevalent SARS-CoV-2 variants in Spain in subjects ≥18 years was investigated for 6 months in HIPRA-HH-2 open-label extension study. Subjects received a fourth dose of PHH-1V after either two BNT162b2 doses plus one PHH-1V dose (cohort 1) or three BNT162b2 doses (cohort 2). As regulatory endpoint, neutralization titers were investigated for PHH-1 V as fourth dose vs BNT162b2 as third dose in subjects receiving previous BNT162b2-based regimens. PHH-1 V immunogenicity (GMT) was investigated against Beta, Delta, and Omicron BA.1, BA.4/5 and XBB.1.5 on Days 14, 98 and 182 post-immunization. Two hundred and eighty-eight subjects received PHH-1V. Neutralizing antibodies against Omicron BA.1 at Day 14 significantly increased after the PHH-1V as fourth booster vs the third BNT162b2 booster (GMT ratio 0.43 (95% CI: 0.28; 0.65; p-value < .0001)). PHH-1V fourth booster induced a significant increase in neutralizing titers vs baseline (GMFR on Day 14 [95% CI]: Beta 6.96 [5.23, 9.25]; Delta 6.27 [4.79, 8.22]; Omicron BA.1 9.21 [5.57, 15.21]; Omicron BA.4/5 11.80 [8.29, 16.80]; Omicron XBB.1.5 5.22 [3.97, 6.87]), remaining significantly higher up to 6 months. The most frequent adverse events were injection site pain and fatigue. As conclusion, PHH-1V booster induced sustained humoral and cellular immune response against Beta, Delta variants and cross reactivity against distant Omicron subvariants and could be an appropriate strategy for implementing heterologous vaccination campaigns.