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Alternating vaccine dose study launches in London

Researchers running the Com-Cov study investigating alternating doses of the Oxford-AstraZeneca vaccine and the Pfizer vaccine, have announced a new study in London now including the Moderna and Novavax vaccines.

The additional study will seek to recruit adults aged over 50 who have received their first, or ‘prime’ vaccination in the past 8-12 weeks, and will be run at University College London Hospitals NHS Foundation Trust (UCLH), St George’s University Hospitals NHS Foundation Trust and Guy’s and St Thomas’ NHS Foundation Trust. Led by the University of Oxford, the study will be run by the National Immunisation Schedule Evaluation Consortium (NISEC) across nine National Institute for Health Research (NIHR) supported sites. It is backed through funding from the Vaccines Taskforce and the Coalition for Epidemic Preparedness Innovations.

Study participants, who will have already received either the Oxford-AstraZeneca, or Pfizer vaccine, will be randomly allocated to receive either the same vaccine for their second dose, or a dose of the COVID-19 vaccines produced by Moderna or Novavax.

The six new ‘arms’ of the trial will each recruit 175 candidates, adding a further 1050 recruits into the Com-Cov programme.

Working across nine sites in the UK, the researchers will study reactogenicity (any adverse reactions) and the immune system responses to these new combinations of vaccines. The study is designed as a so-called ‘non-inferiority’ study and will compare the immune system responses to the gold-standard responses reported in previous clinical trials of each vaccine.

If the study shows promising results, the regulators MHRA and JCVI would formally assess the safety and efficacy of any new vaccination regimen before it would be rolled out to patients.

Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, and Chief Investigator on the trial said:

“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.

“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.”

Dr Anna Goodman, Consultant in infectious diseases at Guy’s and St Thomas’, said: “This trial will test different vaccines to see if participants develop a good immune response to the virus from these combinations. The hope is that by showing this we will be able to broaden the range of vaccines available for use.”

Dr Alberto San Francisco Ramos, Clinical Research Fellow and Lead Doctor on the study at St George’s, University of London , said:

“We will recruit adults over 50 years old that have already received a single dose of the Pfizer or Oxford vaccines in the NHS rollout. For their second dose, participants will be randomised to receive a single dose of either the same vaccine they originally received or, alternatively, a single dose of the Moderna or Novavax vaccines.

“If we can show that these vaccine combinations are both safe and induce similar immune responses, this could provide flexibility for the national COVID-19 vaccine roll-out.”

Professor Vincenzo Libri, Director of the NIHR UCLH Clinical Research Facility and the UCLH Vaccine Research Centre, who is Principal Investigator of the ComCov trial at UCLH, said:

“As in the first part of the trial, we hope to be able to show that combining vaccines can generate an immune response that is as good and as safe as using the same vaccine for both doses. This would give us flexibility in terms of the vaccine roll out.

“We encourage people from across our local communities to register their interest in taking part.”

If you are interested in taking part in the study, please visit: