A new government-funded clinical trial in the UK will investigate whether a third dose of COVID-19 vaccine for people with weakened immune systems gives a stronger immune response than two doses.

The study, Octave Duo, will offer people who are immunosuppressed or immunocompromised a Pfizer, Moderna or Novavax vaccine as a third 'booster' vaccine.

The £2.2m study will build on the Octave trial, led by the University of Glasgow and co-ordinated by the University of Birmingham’s Cancer Research UK Clinical Trials Unit, which showed that 89% of people who are immunocompromised or immunosuppressed generate antibodies, and 60% generate a strong antibody response after two doses. However, 40% of people in these groups mounted a low, or undetectable, immune response after two doses, and the level of antibody response varies between the groups studied.

Dr Rob Buckle, chief scientist of the Medical Research Council, part of UKRI, which co-funded the trial, said: “Today’s results investigating the outcome for people with immunosuppression will be of concern to the subset for whom the vaccine didn’t trigger a large protective response. This new study of giving third jabs to this group is critical research which we hope will demonstrate a much-needed immunity boost or identify those who could benefit from other interventions.”

Initial results are expected later this year to inform the UK’s COVID-19 vaccine deployment in these specific at-risk groups. The trial will follow the patients to mid-2022 and offer more detailed information at that stage.