Two COVID-19 vaccine candidates created by the Peter Doherty Institute for Infection and Immunity and Monash Institute of Pharmaceutical Sciences are moving into the Phase 1 clinical trial stage, with both projects looking for healthy volunteers.
The new vaccine candidates are distinct from existing vaccines in use globally because they focus on the immune response on the tip of the SARS-CoV-2 spike protein, called the receptor binding domain (RBD).
The RBD enables the virus to enter and infect cells in the body, eliciting more than 90 per cent of neutralising antibodies which can block the virus following SARS-CoV-2 infection.
The two candidates are:
- RBD protein vaccine – it uses part of the virus protein, rather than genetic material or another virus, to elicit an immune response.
- RBD mRNA vaccine – represents the virus genetic sequence that codes for the tip of the spike, which will lead to the production of the RBD protein.
According to the Doherty Institute, both candidates are ‘proof-of-principle’ variant vaccines that present the Beta variant to the immune system - the variant of concern back when the vaccines were being designed.
This is important at this point in the pandemic, as the Beta variant has two of the same key RBD mutations as the Omicron variants currently spreading through Australia (BA.1 and BA.2), so the scientists behind the candidates hope they may also improve immunity to Omicron.
University of Melbourne Professor Terry Nolan, head of the Vaccine and Immunisation Research Group at the Doherty Institute, will lead the Phase 1 trial and is recruiting 114 volunteers to participate.
“This trial will assess the safety and efficacy of a single dose of these vaccines as a fourth dose of a COVID-19 vaccine, therefore participants must have had their third dose at least three months prior to the study commencing,” Professor Nolan said.
“People who have been infected with COVID-19 are also eligible provided they had their infection at least three months prior, and have had their third vaccine dose.
“What’s also unique about this gold standard, randomised, double-blind, placebo-controlled trial is that it will be the first time a side-by-side comparison will be undertaken of two new COVID-19 vaccine platforms.”
Dr Georgia Deliyannis from the University of Melbourne performed most of the RBD protein vaccine experiments at the Doherty Institute, and said in pre-clinical trials the vaccine induced high levels of RBD-specific antibodies, including high neutralising antibodies following two doses.
“Immunity induced by the RBD protein vaccine protects against virus challenge in a mouse model of SARS-CoV-2 infection, even 100 days following the boost,” Dr Deliyannis said.
“As well as inducing strong neutralising antibody immunity to the Beta variant in mice, it also retains its potential to neutralise the original ancestral strain, and preliminary in-lab studies have demonstrated neutralising activity against other variants including Delta and Omicron.”
Doherty Institute director Professor Sharon Lewin said the need for next generation vaccines using innovative technology remains high, especially as new variants continue to emerge.
“Both vaccines are efficient to produce and can be rapidly modified to incorporate distinct or multiple RBD mutations arising in future variants,” said Professor Lewin.
“In addition, Australia needs the ability to manufacture its own vaccines to ensure our own supply should future global shortages occur, and to contribute to the global need for COVID-19 vaccines.”
Updated at 11.24am AEDT on 25 March 2022.
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