The aim of the study is to assess how well people's immune systems respond when their second "boost" dose is a different type of vaccine to their first "prime" dose.
ADVERTISEMENTA study looking at whether people can receive doses from two different COVID-19 vaccines has been expanded to include the jabs developed by Moderna and Novavax.
The Com-COV trial by researchers from the University of Oxford had until now only included the jabs developed by Pfizer/BioNTech and AstraZeneca/Oxford University — both approved by British authorities in December.
The Moderna vaccine has since also been authorised for use while the Novavax jab is currently under review by the UK Medicines Healthcare Regulatory Agency (MHRA).
The aim of the study is to assess how well people's immune systems respond when their second "boost" dose is a different type of vaccine to their first "prime" dose.
Researchers from the Oxford Vaccine Group believe that this "mix and match" approach could create a more flexible and faster vaccination campaign.
"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," Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford and Chief Investigator on the trial, said in a statement.
"This would also create resilience within the system in the event of a shortfall in availability of any of the vaccines in use," he added.
The study started in February and has so far involved over 800 people. It is now looking for an additional 1,050 participants who must be over 50 and have received their first dose of the vaccine eight to 12 weeks before being enrolled in the study.
It comes after the use of the AstraZeneca vaccine was restricted to certain age groups in Britain and European Union countries last week after regulators warned of a "possible link" between the jab and rare blood clot events.
Both the MHRA and the European Medicines Agency reiterated however that the benefits of using the AstraZeneca vaccine outweigh the potential risks.
The UK has administered more than 40.1 million doses of the vaccines with over 7.8 million people now fully immunised. Over half of the doses administered have been AstraZeneca.
The Anglo-Swedish pharmaceutical has delivered just over 29 million doses of its vaccine to EU member states while Pfizer has provided 69.6 million doses.
Meanwhile, US company Johnson and Johnson announced on Tuesday that it is delaying the roll-out of its Janssen jab to the European Union after six women in the US developed blood clots after vaccination.
More than 6.8 million doses of the Janssen vaccine have been administered States-side.
The Johnson and Johnson vaccine — which has not been approved yet by the UK regulator — is a single-dose jab and will therefore not be included in the Com-COV study.
Chinese authorities are also looking at whether they can mix vaccine after admitting over the weekend that the effectiveness of its two home-grown jabs is low.