A new vaccine being developed by scientists in Austria is effective against all SARS-CoV-2 variants known to date, including Omicron, even in those who have not yet built up any immunity as a result of immunisation, according to the preclinical data.

The antigen-based vaccine developed at MedUni Vienna targets the receptor-binding domains (RBD) of the SARS-CoV-2 virus and induced a robust and uniform RBD-specific IgG antibody response in experimental models and human tests.

This antibody response prevents the virus from docking onto and entering the body's cells so that infection cannot occur, the researchers said. The SARS-CoV-2 subunit vaccine (PreS-RBD) is based on a structurally folded fusion protein consisting of two RBD of the SARS-CoV-2 virus and the PreS antigen from hepatitis B, which serve as immunological carriers for each other, thereby strengthening the immune response, they said.

The researchers noted that currently available genetic SARS-CoV-2 vaccines induce mainly transient IgG1 antibody responses, whereas the PreS-RBD vaccine can additionally induce long-lived RBD-specific IgG4 antibodies. According to the findings published in the journal Allergy, PreS-RBD-specific IgG antibodies detected in blood and mucosal secretions reacted with SARS-CoV-2 variants, including the Omicron variant.

Antibodies induced by vaccination with PreS-RBD more potently inhibited the binding of RBD with its human receptor ACE2, the researchers said. Their virus-neutralising titers were higher than those in a random sample of individuals fully immunised with two vaccinations of currently registered vaccines or than those of individuals who had previously had COVID-19, they said.

"The PreS-RBD vaccine has the potential to induce sterilising immunity to old and new SARS-CoV-2 variants by preventing infection by stopping viral replication and transmission through the inhibition of cellular virus entry," said study leader Rudolf Valenta. It is also expected that the vaccine will even be effective in people who have not previously responded to vaccination, as they will receive additional T-cell support from the PreS portion of the vaccine.

An earlier study by the team had found that approximately 20 per cent of those recovered from COVID-19 failed to form RBD-specific antibodies and were thus at constant risk of re-infection. Previous work on allergy vaccines and clinical trials also conducted with PreS-based allergy vaccines have demonstrated the safety of PreS-based vaccines, even when used repeatedly.

"Our data give us grounds to hope that this readily producible protein-based vaccine antigen will be effective against all SARS-CoV-2 variants known to date, including Omicron," said Valenta.

"The vaccine is designed to enable repeated injections to build up sustained sterilising immunity, is suitable for use in all age and risk groups and appears to be superior to currently available vaccines when it comes to inducing neutralising antibodies," he said. The first clinical trials of the vaccine required for approval could be carried out this year if sufficient funding is available, the researchers added.