A team of researchers has developed a novel trivalent recombinant protein vaccine that shows promising results in generating broad protection against multiple SARS-CoV-2 variants, including the immune-evasive XBB lineages.
Innovative Vaccine Design and Development
The new vaccine, dubbed Tri-Vac, incorporates receptor-binding domain (RBD) sequences from three different SARS-CoV-2 variants - Delta, BA.5, and XBB.1.5 - in a 1:1:4 ratio. The vaccine's design features a self-assembled trimeric protein structure that clusters three RBD molecules on one side and HR1/HR2 helices on the other, creating a distinctive bouquet-like shape.
Robust Preclinical Results
In mouse studies, Tri-Vac demonstrated several key advantages:
- Generated high levels of RBD-specific IgG with endpoint titers exceeding 106
- Induced broad-spectrum neutralizing antibodies against multiple variants
- Provided effective protection against live XBB.1.16 challenge
- Stimulated robust cellular immune responses and germinal center activity
The vaccine showed particular effectiveness when used as a heterologous booster following initial vaccination with either inactivated or mRNA vaccines, significantly improving neutralization against XBB variants.
Promising Human Trial Outcomes
In a Phase 1 investigator-initiated trial involving 64 participants:
- Both low (30μg) and high (60μg) doses were well-tolerated
- Minimal adverse events reported, mostly mild and transient
- Significant boost in neutralizing antibodies against multiple variants
- Neutralizing activity maintained for over six months
- Effective against recent variants including BA.2.86 and JN.1
The GMT of neutralizing antibodies increased substantially across all tested variants, with particularly impressive improvements against XBB lineages. For instance, in the high-dose group, neutralization against XBB.1.5 increased 16.3-fold compared to pre-vaccination levels.
Safety Profile
The vaccine demonstrated an excellent safety profile in human trials:
- Only 25% of high-dose and 18.75% of low-dose recipients reported mild adverse events
- Most common side effect was injection site pain
- No serious adverse events reported within 6 months of vaccination
Long-term Protection
Follow-up studies at six months post-vaccination showed:
- Maintained neutralizing activity in both dosage groups
- Sustained protection against XBB.1.5 and JN.1 variants
- GMTs exceeding 800 against XBB.1.5 and 600 against JN.1
This new vaccine platform represents a significant advancement in COVID-19 vaccine development, particularly in addressing the challenge of variant escape. Its ability to generate broad neutralizing responses and function effectively as a heterologous booster makes it a promising candidate for future vaccination strategies.
