Launched in February, the world-first ‘Com-Cov’ trial is seeing whether the first dose of one vaccine type can be mixed with a second dose of a different type: thus giving vaccination campaigns more flexibility in the eventuality of a shortfall of one type.
Volunteers in the new trial arms will have already received the first dose of the Oxford-AstraZeneca or Pfizer vaccine (two vaccines authorized and being rolled out in the UK). They will then be randomly allocated a second dose of either the same vaccine, a dose of the Moderna vaccine, or a dose of the Novavax vaccine.
A total of 1050 participants aged 50+ will be added to the program, with 175 in each arm of the trial. This is on top of the 830 participants for the AstraZeneca / Pfizer combination: recruited over eight sites in a two-week period in February.
The study is a ‘non-inferiority’ study – meaning its intent is to demonstrate that mixing is not substantially worse than not mixing. Immune results will be compared to those reported in the original clinical trials for each vaccine.
If the study shows promising results, the Medicines and Healthcare products Regulatory Agency (MHRA) and the government’s Joint Committee on Vaccination and Immunisation (JCVI) would then formally assess the safety and efficacy of the regimen.
“The focus of both this and the original COM-COV study is to explore whether the multiple COVID-19 vaccines that are available can be used more flexibly, with different vaccines being used for the first and second dose," Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, and Chief Investigator on the trial said.
“If we can show that these mixed schedules generate an immune response that is as good as the standard schedules, and without a significant increase in the vaccine reactions, this will potentially allow more people to complete their COVID-19 immunisation course more rapidly.
“This would also create resilience within the system in the event of a shortfall in availability of any of the vaccines in use.”
The trial is led by the University of Oxford, run across nine National Institute for Health Research supported sites by the National Immunisation Schedule Evaluation Consortium, and backed through funding from the Vaccines Taskforce and the Coalition for Epidemic Preparedness Innovations.