The U.K. has delayed the second dose of COVID-19 vaccines to maximize the number of people who can receive the first vaccine dose.  

The move to delay administering the second dose by up to 12 weeks has prompted criticism from some physicians. The British Medical Association criticized the delay as “grossly unfair.”

Dr. Anthony Fauci recently said he disagreed with the strategy in a CNN interview. The U.S. would administer the second dose of the vaccine from Pfizer (NYSE:PFE) and BioNTech (NSDQ:BNTX) three weeks after the first, as the developers have recommended. 

Pfizer warned in a statement that “there is no data to demonstrate that protection after the first dose is sustained after 21 days.”

Spain’s health minister Salvador Illa echoed that sentiment in a recent press briefing today, stating the country would stick by its plan to administer the second Pfizer-BioNTech vaccine dose 21 days after the first.

Germany and Denmark, however, are considering following in the U.K.’s footsteps. 

The efficacy of the first dose of Pfizer-BioNTech vaccine is roughly 50%, said Dr. William C. Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development. The efficacy rises to 95% following the second dose.