A clinical trial has launched today in the UK that will test the effects of using two different COVID-19 vaccines for dose one and dose two. The study – Comparing COVID-19 Vaccine Schedule Combinations, or "Com-COV" – is the first of its kind and will also explore the impact of using different dosing intervals.
The UK's COVID-19 vaccine rollout commenced in December, and requires an individual to receive two doses of the same vaccine, either Pfizer/
Com-COV has been classified as an "Urgent Public Health" study by the National Institutes for Health and Research (NIHR), and its hoped that the data produced may offer greater flexibility for vaccine delivery going forward.
“Given the inevitable challenges of immunizing large numbers of the population against COVID-19 and potential global supply constraints, there are definitely advantages to having data that could support a more flexible immunization program, if ever needed and approved by the medicines regulator," – Jonathan Van-Tam, deputy chief medical officer and senior responsible officer for the study, said in a press release.
The study will run for a 13-month period and will recruit over 800 patients across eight sites in the UK, including London – St George’s and UCL, Oxford, Southampton, Birmingham, Bristol, Nottingham and Liverpool.
Com-COV has eight different arms that will test eight different combinations of doses and dose intervals. This is tentative and subject to change should more COVID-19 vaccines be approved for use in the UK. The eight arms include the following dose combinations:
- Pfizer/BioNTech and Pfizer/BioNTech - 28 days apart
- Pfizer/BioNTech and Pfizer/BioNTech - 12 weeks apart – (control group)
- Oxford/AstraZeneca and Oxford/AstraZeneca - 28 days apart
- Oxford/AstraZeneca and Oxford/AstraZeneca - 12 weeks apart – (control group)
- Oxford/AstraZeneca and Pfizer/BioNTech - 28 days apart
- Oxford/AstraZeneca and Pfizer/BioNTech - 12 weeks apart
- Pfizer/BioNTech and Oxford/AstraZeneca - 28 days apart
- Pfizer/BioNTech and Oxford/AstraZeneca - 12 weeks apart
Aside from the logistical benefits of using alternative vaccines, there is scientific value to exploring how different vaccines and doses affect the human immune system.
Dr Peter English, consultant in communicable disease control, pointed out that the antigen used across the currently authorized COVID-19 vaccines is the same Spike protein. Therefore, the immune system can be expected to respond just as well if a different product is used for boosting. “It is also the case that many vaccines work better if a different vaccine is used for boosting – an approach described as heterologous boosting," English said, referencing previously successful trials using Hepatitis B vaccines.
“It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know," added Van-Tam.
If warranted by the study data, the Medicines and Healthcare products Regulatory Agency may consider reviewing and authorizing modifications to the UK's vaccine regimen approach – but only time will tell.
"We need people from all backgrounds to take part in this trial, so that we can ensure we have vaccine options suitable for all. Signing up to volunteer for vaccine studies is quick and easy via the NHS Vaccine Research Registry," Professor Andrew Ustianowski, national clinical lead for the NIHR COVID Vaccine Research Program, said