Postponing the second dose of Covid-19 vaccines is "very risky" because the efficacy data was based on a specific dosage schedule, a former FDA director told CNBC on Thursday.
His comments came after the UK's decision to give a second shot of the coronavirus vaccine 12 weeks after the first dose, contrary to the recommendations of the vaccine manufacturers. Germany is reportedly considering a similar move, while Denmark approves a six-week gap between doses.
The vaccines approved for use in the UK both require two doses.
American pharmaceutical company Pfizer and German biotechnology company BioNTech recommended giving the second dose of their vaccine 21 days after the first. British-Swedish pharmaceutical company AstraZeneca said the vaccine, jointly developed with Oxford, requires two doses to be given one month apart. The UK initially said it would follow this schedule.
It's a very risky endeavor because if it fails, you will be worse off.
Former FDA director
Any decision to change dosing schedules should be based on data, said Norman Baylor, a former director in the US Food and Drug Administration's office for vaccine research and testing.
"It is very risky to try to extend the gap between two doses or to give a dose when there is no data," he told CNBC's Street Signs Asia on Thursday.
"I understand a few reasons for this, but again, it's not really data-driven," said Baylor, who is also president and chief executive officer of Biologics Consulting. "It's a very risky endeavor because if it fails, you will be worse."
The UK's controversial decision came as the country continued grappling with a new strain of the coronavirus that is spreading faster, despite no evidence that it is more severe or deadly. 62,322 cases were reported on Wednesday, and more than 2.8 million people have tested positive for the virus to date, according to government figures.
A nurse prepares the Oxford-AstraZeneca vaccine at Pontcae medical practice in Merthyr Tydfil, Wales on January 4, 2021.
Matthew Horwood | Getty Images News | Getty Images
Delaying the second dose of the vaccine means more people can get their first dose. However, Baylor said it was ideal to follow the dosing regimen from the vaccine's effectiveness studies.
"If you don't have the data, you are taking a risk there," he said. "That is the point, the risk you are taking."