We would like to thank all our Com-COV and Com-COV2 study volunteers for their participation in these trials. Data from these studies have affected vaccine policy in the UK, and around the world.
Links to all publications arising from these trials can be found on the NISEC website. We will update this page whenever we have new information relating to our participants.
In the Com-COV study we have so far found that immunisation with the two ‘mixed’ schedules (Oxford/AstraZeneca followed by Pfizer or Pfizer followed by Oxford/AstraZeneca) produce antibody and T cell responses higher than that seen after two doses of the Oxford/AstraZeneca, which is known to be a highly effective vaccine schedule against severe disease. Short-term side effects were slightly higher after the second dose in people who receive a “mixed” schedule, but there were no safety concerns raised in the study.
Increasing the ‘priming interval’ (the time between first and second vaccine doses) from four to twelve weeks increased the neutralising antibody response of all four vaccine schedules. The T-cell response, conversely was lower in the 12-week groups. The short-term side-effects seen following vaccination were reduced with a longer priming interval in schedules which had Pfizer as a second dose.
In the Com-COV2 study we found that all the studied mixed-schedules (Oxford/AstraZeneca followed by Novavax or Moderna and Pfizer followed by Novavax or Moderna) produced a robust response both in terms of antibody and T-cells. All combinations produced antibodies that were higher than two doses of the Oxford/AstraZeneca vaccine. Short-term side effects after vaccination were higher in people who had Moderna as a second dose, but not in those who had Novavax.
Further results from Com-COV2 show that immune system antibody responses (neutralising antibodies) against the Omicron variant are lower in people who have had two doses of Oxford/AstraZeneca than two doses of Pfizer COVID-19 vaccine.
The most recent results from Com-COV2 look at how well the immune response is maintained over time. The higher antibody levels that were seen in all schedules fell at approximately the same rate for all schedules.
The antibodies produced by infection and vaccination can have many different functions. One of those functions is ‘neutralisation’, whereby the antibody stops the virus from entering the cell. The Pfizer/Novavax overall had a lower antibody response than Pfizer/Pfizer, but the neutralising antibody response was in fact greater.
The results from both these studies have been very reassuring, as they have shown that mixed vaccine schedules are well tolerated and able to produce robust immune system responses that are at least as good as or higher that of the Oxford/AstraZeneca vaccine – a vaccine that we know has very high real-world protection against severe disease and death.
These results are important because they show that countries can be more flexible in their approach to vaccination, potentially improving access to COVID-19 vaccines.
They also show that there may be subtle but important differences between the vaccines which affect exactly what kind of immune response each combination of vaccines produces, which will inform future vaccine development.
We would like to thank you all again for your participation in Com-COV and Com-COV2. It is greatly valued. The results from the trial are still giving interesting and useful findings. We will keep you informed of further publications in the future.
Although new data produced from these trials is unlikely to have any direct clinical impact on our participants now, we would strongly encourage all our participants to follow government guidance regarding receipt of further vaccine doses.
General information for COVID-19 vaccine trial participants from the National Institute of Health Research can be found here:
The Oxford Vaccine Group