U.K. to test mixing COVID-19 vaccines in world-first trial

• He added it "could provide clues as to how to increase the breadth of protection against new virus strains."

How it works: More than 800 volunteers over 50 years old will be given the Oxford University-AstraZeneca coronavirus vaccine followed by a dose of Pfizer-BioNTech's, or vice-versa, according to the U.K. government statement.

• There will be a four- or 12-week break between doses.

What to watch: The study will run for 13 months, but initial findings are expected to be released in the summer.

What they're saying: "It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer," said deputy chief medical officer Professor Jonathan Van-Tam, the senior responsible officer for the study.

• "Unless this is evaluated in a clinical trial we just won't know."

Of note: The FDA said last month it's following discussions, such as "mixing and matching vaccines in order to immunize more people against COVID-19."

• But "without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19."