Could combining Pfizer's and AZ's COVID-19 vaccines fill supply gaps? U.K. researchers aim to find out

Given that the COVID-19 vaccines from Pfizer and AstraZeneca each require one dose, followed a few weeks later by a booster shot, could the two products be used interchangeably? That’s the question researchers from the Oxford Vaccine Group have set out to answer with a new clinical trial designed to address a mounting problem: The demand for COVID vaccination in many locales around the world is far outstripping the supply. Oxford’s 13-month study will recruit more than 800 volunteers in England, who will receive one of four different combinations of the vaccines. Half the participants will get two doses of the same vaccine, while the others will receive one dose of either the Pfizer or AstraZeneca vaccine, followed by a booster of the other company’s product.