The coronavirus threat in the US is likely to be on the low side this summer, but there is no guarantee that it will stay that way later this year, said Dr. Scott Gottlieb told CNBC on Friday.

“I don’t think we should declare the mission accomplished. I think we should declare a short-term victory,” the former commissioner of the Food and Drug Administration said on Squawk Box.

Coronavirus cases in the country have fallen as more Americans are vaccinated against Covid. According to a CNBC analysis of Johns Hopkins University data, the 7-day average of new infections a day is 23,000. That has fallen by more than 50% since the beginning of May alone.

“I think we’ve done enough to give ourselves the opportunity to enjoy the summer and take a low risk this summer,” said Gottlieb, who headed the FDA from 2017 to 2019 and is now on the board of directors at vaccine company Pfizer . However, he added, “I think this will be a risk when we get into autumn and probably earlier into winter.”

One reason for the cautious outlook for the colder months is that “we were able to see new variants,” said Gottlieb, who previously determined that respiratory pathogens such as the coronavirus generally spread more easily in winter. “I think we need to get better monitoring and sequencing of the strains so we can spot these variants faster,” he said.

The US cannot relax its efforts to have more people vaccinated either, said Gottlieb. This is a key factor in reducing risk across the country.

Around 50% of the country’s population had received at least one dose by Thursday, according to the Centers for Disease Control and Prevention. Gottlieb suggested that around 75% of the country could be vaccinated by the fall.

“So there is still a lot to be done. Right now we are on a pretty good way to do the right things,” he said.

Disclosure: Scott Gottlieb is a CNBC employee and a member of the boards of directors of Pfizer, genetic testing startup Tempus, healthcare technology company Aetion, and Illumina biotech. He is also co-chair of the Healthy Sail Panel for Norwegian Cruise Line Holdings and Royal Caribbean.