Pharmaceutical company Pfizer and its German partner BioNTech on Monday warned that they have no evidence to suggest that their jointly developed coronavirus vaccine would protect against the infection if the booster shot was administered later than 21 days, which was tested in trials, Reuters reported.

This came after Germany was considering whether to allow a delay in administering a second dose of the vaccine amid criticism that the government has failed to procure enough vaccines for all the citizens. On Monday, Denmark approved a delay of up to six weeks between the first and second shots of the vaccine from BioNTech and Pfizer. Last week, the United Kingdom had spaced out the dosing regimen amid growing concerns over a more infectious strain of the virus.

However, both the companies in a statement pointed to a lack of trial data to support delaying the second dose as countries try to vaccinate as many people as possible by giving them one shot.

“The safety and efficacy of the vaccine has not been evaluated on different dosing schedules as the majority of trial participants received the second dose within the window specified in the study design,” the companies said. “There is no data to demonstrate that protection after the first dose is sustained after 21 days.”

Under the UK government’s plan, second doses of the vaccine could be administered as many as 12 weeks later, longer than the three-week timing determined by the companies, according to Bloomberg.

Globally, the coronavirus has infected more than 8.56 crore people and killed over 18.52 lakh, according to the Johns Hopkins University data. More than 4.8 crore people have recovered from the infection in the world.