Washington(CNN) Colorado Gov. Jared Polis on Sunday said he is worried about the potential for a second spike in coronavirus cases as the state begins loosening restrictions this week.

The Democrat announced early last week that the state would move into a "Safer At Home" phase on Monday, April 27, in which residents would not be ordered to stay in their home but are encouraged to stay there as much as possible. Polis told CNN's Jake Tapper on "State of the Union" Sunday that the more aggressive, stay-at-home measure "has been effective in leveling and plateauing the curve which is absolutely critical if we're going to in ... any way sustain the social distancing," while adding, "We don't even have an end date in sight until there's a vaccine or cure."

Asked about a warning from the Colorado School of Public Health about the threat of a second spike in cases, Polis told Tapper, "Yeah, we're all worried about a potential for a second spike, whether it's in the Fall, along with flu season in September/October, whether it's July."

"It's why we've really been really laser focused as an administration on figuring out how we can endure and sustain," he added.

The governor, when asked if he would reissue another stay-at-home order if he saw a new surge in Covid-19 cases, told Tapper he would look at data and "adjust in real time" as needed.

"We'll have to adjust, and we expect that we'll have to adjust the degree of social distancing in real time, meaning we're going to look at those early indicators, the mobility data," he said. "We're going to look at disease data. We're going to look at a number of different proxies. And as we need to, adjust it in real time."

Under the state's Safer-At-Home phase, retail businesses with curbside delivery can reopen and elective medical procedures can resume. Gyms, spas and night clubs will stay closed, while businesses such as dog grooming, tattoo parlors and personal training can open with strict precaution.

As of Sunday morning, there were more than 939,000 confirmed coronavirus cases in the United States and at least 53,000 deaths, with more than 12,900 cases and at least 684 deaths in Colorado alone.

Asked by Tapper if he was worried his decision to reopen the state could cost lives, Polis said, "We have to make the best informed decisions based on data and science with the information we have."

"What we know is that what matters a lot more than the date that the stay-at-home order ends is what we do going forward," he said. "And how we have an ongoing, sustainable way, psychologically, economically and from a health perspective, to have the social distancing we need at the workplace."