Related video above: Air travel picks up as more people get vaccinatedWould-be travelers are crooning a new theme song: "Come fly with me, let's fly, let's fly away."Bottled up yearnings to visit people and places — perhaps even some Frank Sinatra made famous — have vaccinated folks (and a bunch who aren't) setting pandemic-era records at U.S. airport checkpoints.In the European Union, the UK and other corners of the globe, officials are currently considering ways to restart international travel this summer.When that occurs, cinch up your seat belt — traveler numbers will soar.The U.S. Centers for Disease Control and Prevention recently eased its domestic and international travel guidance for vaccinated people, stating that travelers who are fully vaccinated "can travel safely within the United States" but noted a greater risk for international travel.However, the agency is still discouraging nonessential travel due to rising numbers of COVID-19 infections. Driven by extremely contagious variants that have invaded all 50 states, the virus is currently hitting healthier 30- to 50-year-olds hard. Globally, COVID-19 cases climbed for the sixth consecutive week as of April 6, according to World Health Organization statistics, with over 4 million new cases and 71,000 deaths.Is it truly safe to travel by air right now, even if you're fully vaccinated?Related video: Passengers begin returning to airportsCase count, masks and ventilation are key"There are three factors to consider," said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech, who studies the airborne transmission of COVID-19."How prevalent is the virus in the population? If it's highly prevalent, then there's a good chance that someone who is infected is going to be on a plane," Marr said.Why does that matter if you're vaccinated? "We're still learning how effective the vaccines are against variants of the virus," the CDC said recently, as well as "how long COVID-19 vaccines can protect people."In addition, real world studies of the Pfizer-BioNTech and Moderna vaccines show they are still 90% protective against the coronavirus — but that means it's still possible to get infected."Is everyone masked? That's also very important," said Marr, who is world renowned for her 2011 discovery that influenza can hover in air for an hour via respiratory microscopic droplets called aerosols."Vaccinated people could potentially still get COVID-19 and spread it to others," according to the CDC, as respiratory droplets fall onto surfaces or float in the air. "We're still learning how well COVID-19 vaccines keep people from spreading the disease," the agency added.Early in the pandemic, according to a CDC investigation, an unmasked passenger with no symptoms infected 12 fellow business class travelers, two people seated in economy and one crew member on a 10-hour international flight.Last summer, 13 asymptomatic people on an international flight into Ireland infected another 46 people in six regions of the country, despite some use of masks on the plane. And in September, nine people tested positive after a flight from India to New Zealand, despite the fact that masks were mandatory on the plane."The risk for on-board transmission of SARS-CoV-2 during long flights is real," the CDC investigation stated. "Long flights not only can lead to importation of COVID-19 cases but also can provide conditions for superspreader events."Still, a Harvard University report released last October concluded the risk of catching COVID-19 on an airplane is rare, as long as people are masked, the airport uses safety precautions and the planes have installed HEPA, or "high efficiency particulate air" filters. The HEPA filters are rated to remove 99.97% of dust, pollen, mold, bacteria and other airborne particles with a size of 0.3 microns. COVID-19 is thought to be between 0.06 to 1.4 microns.Which brings Linsey Marr to her third point: "Finally, air travel safety could be improved if airlines and manufacturers install and use HEPA filters properly in more planes. Proper filtration is a key to safe air travel."What to do to fly more safelyWhile there may not be much you can do about CO2 levels or HEPA filtration (other than ask the airline and make your concerns known), experts say there are key actions you can take to make your flight safer — in addition to getting vaccinated as soon as you can.Fly short distances. "If the plane doesn't have HEPA filtration, and it's a short flight, under an hour, then you might be OK. But then it's even more important that people are masked the entire time," Marr said.If your destination is further, Marr suggests driving part of the way and flying the rest."If you must fly, try to take flights with the fewest stops or layovers," the CDC advises. "Spending time in security lines and airport terminals ... can bring you in close contact with other people and frequently touched surfaces."Plan your ride to the airport.If you have to take an Uber, Lyft or taxi to the airport, make sure you, your family and the driver are all masked throughout the journey — and be sure to roll down the windows to encourage air flow, Allen said."We've done some modeling on this, we're showing that even rolling down the windows just a couple inches can really help with airborne transmission," Allen said. "And you want to put down the windows even if it's inclement weather. A little bit will really help."Follow safety protocols.Even fully vaccinated people need to continue to follow the triad of key safety steps, the CDC said: "Wear a mask over your nose and mouth, stay 6 feet from others and avoid crowds, and wash your hands often or use hand sanitizer."Under the Biden Administration, masks are now mandatory on any form of public transportation, as well as transportation hubs such as airports and bus stations.But people don't always comply on planes, as Marr experienced on a recent trip where flight attendants had to admonish passengers to stop removing masks.Consistent masking is especially important if a plane doesn't have HEPA filtration and people are talking, Marr said."This is exactly when it's most important for people to be wearing a mask because talking produces more aerosols than just breathing," she said.Do doublemask and watch the fit.A CDC study found layering a cloth mask over a medical mask, such as a disposable blue surgical mask, created a tighter fit and blocked 92.5% of potentially infectious particles from escaping. Look for 2- to 3-ply mask made of a tight weave of 100% cotton, according to studies.The mask should have a nose wire, the CDC says. Bend it tightly across the nose to keep the mask close to your face. That also helps with fogging if you wear glasses.Stay away from bandanas and gaiter masks unless that's all that's available. A study last year found both types to be the least effective in terms of protectionCarry the essentials.Along with that highly protective mask, you should bring disinfecting wipes and a 3-ounce bottle of hand sanitizer with greater than 60% ethanol or 70% isopropyl alcohol -- the level needed to kill most coronaviruses, according to the CDC.Before you sit, use sanitizing wipes on your seat, tray table and arm rest on the plane, and don't forget your seat belt, the filtration nozzle and light buttons above your head, the video monitor and the back of the seat in front of you.Bring your own ear buds, neck pillow and blanket if you think you need them, and don't forget to bring snacks from home you can eat quickly, to minimize the time you're unmasked. Dried fruit, nuts, or cheese and crackers are good choices. Most airlines have reduced meal service to a minimum.Stay in your seat if you can.Getting up and moving around puts you closer to others on the plane, and visiting the bathroom opens up a whole new set of potentially germ-covered things to touch. If you must take a bathroom break on the plane, have hand sanitizer at the ready.What's best, experts say, is to prepare in advance by having your meals and bathroom breaks before or after the flight.