For some homebound travelers yearning for a vacation, the question isn't whether to book a vacation this year, but when.
Enthusiasm for travel is at its highest point in a year, with 87% of American travelers expected to take a trip this summer, according to a survey conducted last week by travel market research company Destination Analysts.
But is the summer the best time to travel this year, or is it prudent to wait? Medical professionals present several scenarios of how the rest of 2021 may play out.
1. A summer of low infection rates
Dr. Sharon Nachman, chief of the Division of Pediatric Infectious Diseases at Stony Brook Children's Hospital, said she expects this summer to have lower infection rates than the winter.
"When I add in the idea that kids 12 and older will also have access to vaccines this summer, the risk to families will continue to drop, allowing for more activities and with lower risk ... to all," she said.
Dr. Anne Rimoin, a professor of epidemiology at the UCLA Fielding School of Public Health, said she thinks there is "a real chance at a summer with much lower rates of disease, however, it means we all have to pull together and do our part" by getting vaccinated, wearing masks, social distancing and practicing hand hygiene.
As to whether traveling is safe this summer, she said it depends on two factors: vaccinations and variants.
"It all depends upon how many vaccines we get in arms," Rimoin said. "The variants are more contagious, so … those that are not vaccinated are more easily infected."
2. A good summer and a 'mild fall'
Former Food and Drug Administration Commissioner Scott Gottlieb told CNBC's "Squawk Box" in April that he expects infection rates to be "really low" in the United States this summer, which will likely result in "a relatively mild fall."
After that, things may change, he said.
"I think we should be thinking about the late winter," he said. "I think the overall death and disease from Covid, hopefully, will be diminished, but there's a chance that it's going to start to spread again."
Gottlieb said Covid-19 will "transition this year ... from more of a pandemic strain to a seasonal strain." This, however, could change if variants that can "pierce" prior immunity or vaccines develop, though he noted that "right now we don't see that on the horizon."
"I don't think we're going to be having holiday parties in the back room of a crowded restaurant on December 20th," he said. "I think that we're going to have to do things differently as we get into the winter."
"But I think that's going to be a fact of life going forward for a number of years anyway," said Gottlieb.
3. Flare-ups and outbreaks
Dr. Charles Bailey, medical director for infection prevention at Providence St. Joseph Hospital and Providence Mission Hospital, does not view this summer as a safe period for travel before infections return in the fall because he expects outbreaks to continue throughout the year.
He said he anticipates the majority of the United States will continue on a path to normalcy, while areas experience "episodic disease flare-ups — local and regional 'hotspots' — of Covid activity through the remainder of 2021 and into early 2022."
Mark Cameron, epidemiologist and associate professor at Case Western Reserve University's School of Medicine, also doesn't see the summer as a "window of opportunity for perfectly safe travel per se" because of concerns about last summer's surges and the possibility of variant-fueled outbreaks.
He compared the current state of the pandemic to "watching the tick and the tock of an irregular clock pendulum."
"The pandemic could end with the virus circulating unpredictably, with new variants causing outbreaks or epidemics on a semi-regular basis, especially where vaccine availability is low or vaccine hesitancy is high, much like the flu does now," said Cameron.
"The moment we're in — with vaccination rates, variant spread and Covid-19 fatigue competing with each other — is critically important in putting a lid on this virus and its growing penchant for evading our eradication efforts," he said.
4. The chance of another summer surge
William Haseltine, former professor at Harvard Medical School and author of "Variants! The Shape-Shifting Challenge of COVID-19," said there is a risk of another summer surge, and traveling during the summer will only exacerbate the problem.
"The more people choose to travel as an escape from the very real pandemic stress and fatigue, the more we risk another surge of cases this summer," he said.
Haseltine said many people hope warm summer weather will bring a decrease in Covid cases, due to the seasonality of other coronaviruses and influenza viruses.
But as it turns out, this virus is "far less seasonal than many expected it to be," he said. "If you look back at 2020 and the early part of 2021, you'll see that there have been fall surges and winter surges, as one might expect, but there have also been spring surges and summer surges."
While the virus that causes Covid-19 is expected to become seasonal at some point, the UN World Meteorological Organization highlighted in a report that "there is no evidence" that this year will be different from 2020.
Dr. Supriya Narasimhan, chief of infectious diseases at Santa Clara Valley Medical Center, agreed that another summer surge is possible, even in places where vaccines are being aggressively rolled out.
She agreed that Covid is "less seasonal than flu" and said the factors which will affect whether another surge occurs are public compliance with masking, vaccine uptake and variants.
"It is a game of cat-and-mouse with the virus mutating and the only way to stop it is to stop transmission," she said. "We may yet hit a vaccine 'wall' in that people just don't want to take it even if available."
"In my opinion, we need more data to make travel decisions," she said.
Disclosure: Scott Gottlieb is a CNBC contributor and is a member of the boards of Pfizer, genetic testing start-up Tempus, health care tech company Aetion Inc. and biotech company Illumina. He also serves as co-chair of Norwegian Cruise Line Holdings' and Royal Caribbean's "Healthy Sail Panel."