All countries need to be on guard in the fight against Covid-19 before the fall flu season, according to Joshua Sharfstein, vice dean for public health practice and community engagement at the Johns Hopkins Bloomberg School of Public Health.
As the flu picks up in the northern hemisphere in the fall months, there would also be the "complication" of other respiratory viruses circulating, he explained. That would also add to fears that the coronavirus may be more easily transmitted during the winter.
"It was only really the social distancing that was putting a lid on the virus, so if people relax too much, you could expect to see a wave well before the fall," Sharfstein told CNBC's "Squawk Box Asia" on Monday.
He also said there is fear that people with the flu would be in the hospitals at the same time as coronavirus patients, which would be a "double tax" on health-care systems.
Between October and April 4 of this year, more than 410,000 people were hospitalized with the flu and 24,000 died in the U.S., according to estimates from the Centers for Disease Control and Prevention.
The U.S. has reported more than 965,000 coronavirus cases and 54,000 deaths, according to data compiled by Johns Hopkins University.
Some countries in Asia have been successful in their efforts to "tame the virus," Sharfstein said. In particular, he said South Korea and Taiwan have done very well. He also mentioned Singapore's "very strong public health response," despite its recent "setback" in the surge of cases among foreign workers who live in dormitories.
"And I think that we have to look at those examples, and say that there are some things — even in the absence of a treatment and vaccine — that can be done to control the virus and that's really what everybody needs to be doing," he added.
Still, Sharfstein urged all countries to keep a close eye on the situation.
"I think that we're all going to have to be vigilant," Sharfstein warned.