Britain to test combining Pfizer, AstraZeneca vaccines in two-shot regimen

London - Trial to examine immune responses of an initial dose of Pfizer vaccine followed by AstraZeneca shot.

Britain on Thursday launched a trial to assess the immune responses generated if doses of the Covid-19 vaccines from Pfizer Inc and AstraZeneca Plc are combined in a two-shot schedule

The British researchers behind the trial said data on vaccinating people with the two different types of coronavirus vaccines could help understanding of whether shots can be rolled out with greater flexibility around the world. Initial data on immune responses is expected to be generated around June.

The trial will examine the immune responses of an initial dose of Pfizer vaccine followed by a booster of AstraZeneca’s, as well as vice versa, with intervals of 4 and 12 weeks.

Both the mRNA shot developed by Pfizer and Biontech and the adenovirus viral vector vaccine developed by Oxford University and AstraZeneca are currently being rolled out in Britain, with a 12-week gap between two doses of the same vaccine.

It is expected more vaccines will be added to the trial when they are approved and rolled out.

Recruitment for the study starts on Thursday, with over 800 participants expected to take part, the researchers said. That makes it much smaller than the clinical trials that have been used to determine efficacy of the vaccines individually.