This is a summary, written by members of the CITF Secretariat, of:

Parham KA, Kim GN, Saeedian N, Ninkov M, Richer CG, Li Y, Wu K, Rashu R, Barr SD, Arts EJ, Haeryfar S.MM, Kang CY, Troyer RM. Monovalent and trivalent VSV-based COVID-19 vaccines elicit potent neutralizing antibodies and immunodominant CD8+ T cells against diverse SARS-CoV-2 variants. bioRxiv 2022.07.19.500626; doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

In a preprint, not yet peer-reviewed, a CITF-funded study led by Dr. Ryan Troyer (Western University) developed four spike-based vaccines against the SARS-CoV-2 virus and measured antibody and cellular responses. All four – one based on the wildtype (original strain), one based on Beta, one based on Delta and a trivalent vaccine combining all three – produced a strong neutralizing antibody response against all SARS-CoV-2 variants in an animal model, including against the  Omicron variant.

A recombinant vesicular stomatitis virus (rVSV) platform was used to generate the vaccines. Blood from mice immunized with various combinations of the four vaccines were obtained to measure antibody and cellular immunity.

Key findings:

  • A prime-vaccination (first dose) with the trivalent vaccine with a booster of the same trivalent vaccine (trivalent/trivalent) consistently produced a neutralizing antibody response against all SARS-CoV-2 variants tested, with all of the mice generating neutralizing antibodies.
    • The trivalent/trivalent regimen was the most effective, with a 10.9-fold increase in neutralizing the Delta variant.
  • For Omicron, the most highly mutated variant to date, a prime-boost with the Delta/Delta vaccine was the most effective (1.5 fold increase in neutralizing titer), followed by the trivalent/trivalent regimen (1.3 fold). The wildtype/wildtype vaccine was equally as effective as wildtype/Delta vaccine in neutralizing the virus (1.0 and 0.8 fold, respectively)..
  • All vaccines induced a spike-specific CD8+T cell response.
    • The greatest CD8+ T cell response was seen in the wildtype/wildtype and Trivalent/Trivalent immunized mice.

The study shows that rVSV is an effective platform for the generation of SARS-CoV-2 vaccines against variants of the original virus that continue to emerge.