Immunogenicity and Safety of PHH-1V COVID-19 Vaccine as a Heterologous Booster in Adolescents.

BACKGROUND AND

OBJECTIVES

PHH-1V, a protein-based, non-mRNA, bivalent, adjuvanted COVID-19 vaccine, has demonstrated strong immunogenicity and favorable safety as a booster in adults. This study evaluated PHH-1V as a heterologous booster in adolescents.

METHODS

HIPRA-HH-3 was a phase IIb, open-label, multicenter, noninferiority trial assessing the immunogenicity and safety of PHH-1V in 240 healthy adolescents (≥ 12 to < 18 years) primed with BNT162b2. Immunogenicity (N = 90) was assessed by measuring neutralizing antibodies against SARS-CoV-2 variants and total binding antibodies in adolescent participants vs young adults (≥ 18 to ≤ 25 years) (N = 81) from a previous trial, who had also been boosted with PHH-1V. T-cell responses at day 14 post booster were also evaluated. Antibody durability and adverse events (AEs) were assessed through day 336.

RESULTS

Neutralizing titers-against Omicron BA.1 (primary endpoint), WH1, Beta, and Delta variants-and total binding antibodies were significantly higher in adolescents than in young adults (P < .001), demonstrating noninferiority (margin < 1.5). T-cell responses against BA.1 and Beta also increased significantly (P < .001). Cross-variant antibody titers remained above baseline (day 0) through day 336. AEs were mostly mild/moderate, primarily injection-site pain and headache within 28 days. No related serious AEs were reported.

CONCLUSIONS

As a heterologous booster in adolescents, PHH-1V is safe and elicits cellular and sustained humoral responses with cross-variant immune recognition, which support the use of PHH-1V in adolescent vaccination strategies. Data in younger and specific risk groups are still needed.