(CNN) With airlines introducing new measures like face masks and intensive sanitization routines to reassure passengers, people have been cautiously returning to air travel even while the coronavirus pandemic continues to spread around the world.

But for some, the notion of climbing aboard an airplane now or in the near future, remains unthinkable. Nothing that airlines, government officials or fellow travelers can say will convince them to step on board.

CNN spoke to some of these self-grounded travelers to find out their biggest concerns about air travel at the moment and what it would take to get them back above 30,000 feet.

For Chris Trinh, a 41-year-old father of four based in Minnesota, the decision to stay off airplanes is partly because of his kids -- his youngest child is only 10 months old and he says he'd be worried about her crawling on the aisle.

It's also, he says, because he feels that no matter how careful he is, he can't guarantee others will be similarly conscientious.

"It's hard to trust other people," he tells CNN.

Trinh's wife is Japanese, and the family usually spend extended vacations in Japan over the summer months. This is the first year they'll be staying in the United States.

"The risk is just too high, and we just don't want to travel," he explains.

Trinh and his family aren't alone. Retired CVS Health engineering manager Vincent Marseglia, 70, is also avoiding flying.

"You're going to be near people, even if they leave the middle seats open," Marseglia tells CNN, speaking from his home in Rhode Island.

Chris Trinh is worried about traveling with his young children.

Courtesy Chris Trinh

"There's no way I'm going to get on a plane. Even before that, you have the crowds at the airports going through security, so you're just exposing yourself."

Wisconsin-based Dean Calin, 60, who's worked in the commercial aircraft industry for more than three decades, has similar trepidations.

Calin says his extensive aviation knowledge makes him more, rather than less, cautious about flying in the age of coronavirus.

"Even though airlines are taking steps to clean the interiors and the air is filtered thoroughly as a process of the air conditioning system, all of that can't counteract the potential contamination that passengers will bring every time the plane is loaded," Calin tells CNN.

"I just don't think that, without a vaccine, there's any safe way to travel yet."

Rethinking plans

Vincent Marseglia and his wife on a train traveling through France in 2016. Right now, they're remaining at home in Rhode Island.

Courtesy Vincent Marseglia

Ruling out air travel means rethinking vacation plans.

Marseglia says that, because of his age, he's being careful in all aspects of his life. He's socially distancing during meetups with his grandkids and wouldn't go on a train either -- nor would he share a car without anyone other than his wife.

Marseglia lives by the ocean in Rhode Island, and he's swapping out dreams of vacations in Italy for local, socially distanced outings in coastal Jamestown.

He's cautious about traveling to other states, given that different regions in the United States have adopted different strategies for quarantining and handling the virus.

But while pouring over photographs of previous adventures in Europe is currently bittersweet, Marseglia's conscious that he's in a privileged position, and so many have been more adversely impacted by Covid-19.

"Even when a vaccine comes available, I'm not going to be the first one to run out and get it," says Marseglia, who points out he's lucky to be able to stay at home and not worry about returning to a workplace.

"I'm willing to wait as long as it takes to get the vaccine, so if it's next year or the year after, I won't make any plans to do any kind of extensive travel until I know that's out there, and it's available and it's effective and I can get it."

Marseglia and his wife in Florence, Italy.

Courtesy Vincent Marseglia

Dean Calin tells CNN he's been self-isolating for over 100 days now, due to concerns about the impact of the virus on his asthma.

As well as working in the aerospace industry, Calin is also a singer in a group. At the beginning of 2020, he was looking forward to aviation-focused business travel trips alongside music gigs across the world. That's all on hold for now.

"It's a sacrifice that we have to make, if we intend to go on living" is Calin's perspective. "It's challenging and it's a different way to live your life, but the alternative is to ignore it is to court death."

Like Marseglia, Calin says would only return to the skies if he'd been vaccinated and he knew the rest of the population had also had time to get the vaccine.

Right now, he calls those who're traveling again "either very brave or very foolish."

"I just don't think that without a vaccine. There's any safe way to travel yet," he says.

How safe is it to travel?

Dr. William Schaffner, an infectious disease expert at Vanderbilt University, tells CNN he does not currently advocate traveling by airplane, particularly in the United States.

"We have been recommending to our patients only really essential travel at present, because in this country, the virus is not under control. It's all over the country and continuing to spread in an inhibited fashion," Schaffner tells CNN.

Schaffner's perspective is people should only travel for personal reasons, in unavoidable circumstances.

"Even then, we ask them to do that very, very cautiously, wearing their masks at all time, keeping social distance," he adds.

Schaffner is principally concerned about the potential for the virus to spread in crowded airports, where it's difficult to maintain social distancing. He also expresses worries about travelers being tightly packed in the cabin.

While some are being cautious, others are returning to air travel.

CNN

"All the hullabaloo having to do with travel often brings you in very close proximity with others in enclosed spaces," he says.

Schaffner is also worried about the impact of traveling back and forth from a spot where there might be a particularly high number of cases.

The infectious disease expert has a vacation home in Florida, where he and his wife usually spend the summer months. They won't be going there this year, he explains. The couple are in the at-risk category due to their ages, which adds to their hesitance, but they're also concerned about the high infection rate in Florida.

"Once we get a vaccine or vaccines, and they can be shown to be reasonably effective and safe and they start to be distributed, then -- if we were vaccinated -- then we can travel," says Schaffner.

Dean Calin, former frequent flier

"And we would be even more comforted if we realize that the large majority of the population out there also received the vaccine," he adds. "I think that will reduce the transmission of this Covid virus, so that then things truly can start to return to normal."

That said, Schaffner's conscious this could be some time off.

"I think this period of caution will be quite extensive, over a period of months, extensive months," says Schaffner.

In the US, Operation Warp Speed is a vaccine program that aims to deliver a Covid-19 vaccine by 2021.

Temporary reality

Trinh is remaining optimistic that his family will one day be able to travel comfortably again.

Courtesy Chris Trinh

Trinh is willing to play the long game when it comes to returning to global travel.

On the day that they would've flown out to Japan, Trinh's wife and kids were upset about the plans that weren't to be. They weren't just sad about the canceled vacation; they don't know when they'll next see their extended family.

But Trinh says he's cautiously optimistic about the future.

"I feel it's just a temporary thing, right? I mean, if it lasts a year, maybe two years, that's just what we have to do," he says. "For me, it's unfortunate that it's happening, but at the same time it's hopefully a once in a lifetime kind of thing."

Trinh is also diplomatic when it comes to reports of other travelers returning to the skies in packed planes.

"I see it as each person's choice," he says. "I mean, as long as everybody accepts the risks that they're taking, I think it's okay."

He's confident there will be a solution, eventually, and his family will board an airplane once again.

"Hopefully it gets better at that point, that we're back to traveling on a yearly basis," he says.

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The people who say they're not boarding an airplane until there's a Covid-19 vaccine - CNN