February 2021: A UK trial has been started to see if giving people different Covid vaccines for their first and second doses works as well as the current approach of giving the same type of vaccine twice.
If there is a proven benefit it would (a) provide more flexibility with vaccine rollout and help deal with any potential disruption to supplies, and (b) scientists say mixing vaccine jabs might also give better protection. No changes would be made to the UK's current approach until at least summer 2021.
Current official guidance from the Joint Committee on Vaccination and Immunisation (JCVI) is that anyone who has had a first dose already should be given the same vaccine for their second dose. (In rare circumstances a different vaccine can be given - if only one vaccine is available or it is not known which was given for the first dose.)
Why is the trial happening? Scientists have good reason to believe that mixing vaccines may prove beneficial; some Ebola immunisation programmes already involve mixing different jabs to improve protection. In the UK mixing doses has happened historically with vaccines for hepatitis, polio, measles, mumps and rubella.
Study details. The Cm-Cov study is run by the National Immunisation Schedule Evaluation Consortium and will involve over 800 volunteers over the age of 50 in England. Some will receive the Oxford jab followed by the Pfizer jab, or vice versa. Some will have the jabs four weeks apart and others 12 weeks apart. Other vaccines may be added to the trial as they are approved by regulators. Results are likely to be published during summer 2021.
Volunteers will be monitored for side-effects and blood tests will check how well their immune systems respond. They are currently being recruited in London, Birmingham, Liverpool, Nottingham, Bristol, Oxford and Southampton.
Why this approach could work. Animal studies have shown a better antibody response with a mixed schedule rather than the same vaccine on both occasions. The trial will test if an enhanced immune response happens in humans, or at least that the response is as good as using the same vaccine twice.
The full study will continue for 13 months, but it is hope that initial findings can be announced by June 2021, and could inform the types of vaccines younger age groups are offered as their second dose. It will also provide data on:
- The impact of the vaccines on new variants.
- The effects of second doses at four and 12 weeks.
Source: BBC News 4 Feb. 2021. Covid trial in UK examines mixing different vaccines. https://www.bbc.co.uk/news/health-55924433
