New low-dose COVID-19 vaccine safely generates immune responses in 80%

09 Feb 2023

A low-dose COVID-19 vaccine harnessing self-amplifying RNA (saRNA) can trigger an immune response in the majority without any serious side effects, according to phase II trial results from the COVAC1 study, recently published in eClinicalMedicine.

The novel saRNA technology uses part of an alphavirus to make copies of the COVID virus spike protein in the muscle cells the vaccine is injected into. The cells quickly produce their own copies of the spike protein, or ‘self-amplify’. This trains the immune system to defend against the virus and recognise it as a threat in future. COVAC1 is the first clinical trial to test this type of vaccine technology for COVID in humans. 

The phase I part of this trial found that the new vaccine technology has the potential to trigger an immune response with an extremely low dose - the lowest of any COVID-19 vaccine across the world.  

This second phase II part of the trial expanded the study to get a clearer idea of how safe and effective the new saRNA vaccine is in a wider range of people, including older adults, those with other pre-existing health conditions, and people with previous immunity to COVID.

The phase II study included 216 adults aged between 18-75 years. Researchers injected participants with two doses (a smaller first dose of 1 micrograms followed by 10 micrograms) of the saRNA vaccine (called LNP-nCoVsaRNA) 14 weeks apart. They collected information about side effects and blood samples to analyse the participants’ immune response to the vaccine.

The study found that 80% of those with no prior COVID-19 immunity had an immune response two weeks after vaccination. Of those who had already been infected with COVID-19 and likely already had some baseline immunity, almost all showed a boost in antibody levels after their first dose. This was similar to the increase in antibodies seen after a third booster dose of currently licensed COVID-19 vaccines.

The study reported no serious side effects related to the vaccine. Common but non-serious reactions included pain at the site of injection, headache and fatigue.

Given the continuing need to protect public health against the threat of COVID-19, these results offer promise that saRNA could provide a low-cost, low-dose booster vaccine in the coming years. 

The COVAC1 trial took place across seven clinical research centres in London and the south-east of England.

This study was co-funded by grants and gifts from the Medical Research Council UKRI and the National Institute for Health Research/Vaccine Task Force, Partners of Citadel and Citadel Securities, Sir Joseph Hotung Charitable Settlement, Jon Moulton Charity Trust, Pierre Andurand and Restore the Earth. Above all, the team acknowledges the participants and dedicated clinics and lab staff who partnered with us to deliver this trial. 

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