Walgreens will begin scheduling doses of the Pfizer coronavirus vaccine three weeks apart, as is recommended by the Centers for Disease Control and Prevention (CDC), following complaints from customers.

The U.S. pharmacy chain has up until now been setting the shots four weeks apart, one week more than is recommended, because the extended schedule made it faster and simpler to schedule appointments, The New York Times reported on Monday.

Starting at the end of the week, Walgreens' vaccine-scheduling system will begin spacing shots three weeks apart, while maintaining the four-week period recommended for Moderna's own vaccine.

Walgreens’ chief medical officer, Kevin Ban, had previously said that spacing the Moderna and Pfizer vaccines the same period apart was "the easiest way to stand up the process based on our capabilities at the time."

Other major pharmacy chains such as CVS and Rite Aid had complied with the CDC's guidance on spacing vaccines apart, the Times notes, spacing Pfizer shots around 20 to 23 days apart.

The newspaper reports that there is no evidence that suggests an extra week reduces the efficacy of the vaccine, and the CDC has said it alright to space the doses as much as six weeks apart.

However, CDC spokesperson Kate Grusich told the Times that Walgreens' scheduling decision still confused its customers and brought on the attention of federal health officials.

According to Walgreens, it has administered more than 8 million coronavirus vaccine doses so far and expects to administer between 26 and 34 million doses by the end of August.