Walgreens has been administering the second dose of Pfizer's[PFE] COVID-19 vaccine a week after federal guidelines say it is ideally delivered, but the chain will change its policy to come into line with the government's recommendations.While the extra time is not feared to be a problem, the Centers for Disease Control and Prevention asked the drugstore chain to follow its guidelines, the New York Times reported Monday.Until now, Walgreens had been administering the second dose of the Pfizer vaccine four weeks after the first, the company confirmed Monday to USA TODAY. Federal guidance is three weeks.We have been automatically scheduling patients’ second doses to occur a minimum of 28 days following their first dose to ensure that no dose is administered earlier than the authorized intervals and patients are able to complete the series vaccination, Walgreens spokesperson Rebekah Pajak said in an email.The company is improving its scheduling system to allow people beginning this week to set their second dose appointment at the three-week timeframe, Pajak said.In some cases, foreign countries, including Canada and Britain, are delaying the second dose of the Pfizer vaccine by months in favor of delivering as many first doses as possible.