UK conducts trial to find out if Coronavirus vaccine can be mixed

UK scientists have launched the world’s first study examining whether different coronavirus vaccines can safely be used for two-dose regimens, an approach they say could give extra flexibility and even boost protection against Covid-19 if approved.

Participants in the 13-month study will be given the Oxford/AstraZeneca and Pfizer/BioNTech vaccines in different combinations and at different intervals, the UK Department of Health and Social Care said in a news release.

“If we do show that these vaccines can be used interchangeably in the same schedule this will greatly increase the flexibility of vaccine delivery, and could provide clues as to how to increase the breadth of protection against new virus strains,” said Matthew Snape, chief investigator and associate professor in pediatrics and vaccinology at the University of Oxford.

Enrollment in the UK government-funded study is currently underway and preliminary results are expected over the summer, the news release said.

The current vaccine dosing regimen for the general public will remain unchanged in the UK, it said. But should the study show promising results, the government may consider revising the recommended vaccine regimen.

The study will also seek to determine if vaccination is more effective with a four-week or 12-week gap between the two doses. More than 800 people are expected to take part in the trial and will begin receiving their shots by mid-February.

Analysis released Wednesday by Oxford scientists but not yet peer-reviewed suggested there could be higher efficacy with more spaced-out doses of the Oxford-AstraZeneca vaccine.

Minister for Covid-19 Vaccine Deployment Nadhim Zahawi said the new trial would provide vital evidence on the safety of the two shots when used in different ways.

“Nothing will be approved for use more widely than the study, or as part of our vaccine deployment program, until researchers and the regulator are absolutely confident the approach is safe and effective,” he said.

Jonathan Van-Tam, England’s deputy chief medical officer, said that given the challenges of rolling out mass vaccination of populations and “potential global supply constraints,” there were advantages to having data to support a more flexible immunization program if needed and approved by the regulator.

“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,” said Van-Tam.

Currently, official guidance from the UK’s Joint Committee on Vaccination and Immunisation states that the second dose should be with the same vaccine as for the first dose. “Switching between vaccines or missing the second dose is not advised as this may affect the duration of protection,” it adds.

However, in certain circumstances where a patient attends a site for a second vaccination and what was given for the first dose is either unknown or unavailable, it is “reasonable to offer one dose of the locally available product to complete the schedule,” guidance states, particularly if the individual is at high risk of infection or is unlikely to attend again.

The US Centers for Disease Control and Prevention (CDC) and the World Health Organization do not currently recommend interchanging coronavirus vaccines, since no data is currently available that examines whether doing so would still provide the same level of protection