The purpose of the clinical trial, which is called COVAC1, is to evaluate whether our new self-amplifying ribonucleic acid (RNA) COVID-19 vaccine candidate is safe and whether it produces immune responses against the coronavirus, SARS-CoV-2.

This is a first-in-human study of a brand new and exciting technology.

One feature of self-amplifying RNA is that it can be used at low doses. It has shown great promise in pre-clinical work.

The study includes both Phase I and II, which are the early phases of clinical vaccine development. The study team progressed to Phase II after the vaccine was shown to be safe in Phase I.

COVAC1 does not have a control or placebo group; everyone receives two doses of active vaccine.

Phase I

  • Six different dose levels of the saRNA COVID-19 vaccine are being evaluated.
  • 120 adult volunteers aged 18 to 45 years have enrolled into the low dose cohort, to test three different dose levels from 0.1 micrograms to 1 microgram.
  • Data from the low dose cohort showed the vaccine was safe and well-tolerated.
  • A further 72 volunteers then enrolled into the higher dose cohort, to test three different dose levels from 1 microgram to 10 micrograms.

Phase II

  • Exploration of safety and immune responses including in older people.
  • A further 222 volunteers aged 18-75 years have been enrolled and have received two doses of the saRNA vaccine.
  • Several research sites across the UK are participating in this part of the study.

What happened at Phase I?

This was the first of multiple steps in the clinical trial and is focussed on evaluating the safety of the vaccine and finding the right dose to give. Different dose levels of the saRNA COVID-19 vaccine have been tested for safety, and the ability to produce an immune response in volunteers.

The study team started with a very low dose (0.1 micrograms) and gradually progressed through the different dose levels up to 10 micrograms.

In total, the Phase I study enrolled 192 adult volunteers in the low dose and higher dose cohorts.

What happens at Phase II and beyond?

Once the team had collected enough data to progress, they started testing the vaccine in a larger population of volunteers. The purpose of this Phase II study is to gather more safety information, particularly in older people as they are most at risk from severe COVID-19. The trial is also continuing to assess immune responses to the vaccine.

To recruit a larger number of participants needed for this trial, multiple clinical research sites across the UK are involved in delivering the study in partnership with Imperial College London.

How do we know if the trial has been successful?

The goal of the trial is to assess both the safety of the candidate COVID-19 saRNA vaccine and the immune responses to it. As this is a new technology, the data from this trial are incredibly important for developing saRNA vaccines.

Safety and tolerability data are reported by the volunteers themselves, either directly by use of a smartphone or laptop, or at trial visits. These data are being collected and reviewed all the time.

Immune responses are tested in the laboratory using a variety of tests. These determine whether there are antibodies that can bind to and block the SARS-CoV-2 virus.


Page updated on 10 March 2021