The air purification systems are for sure better these days in passenger aircrafts. However passengers are not connected directly to those systems with airtight tubes. All passengers are breathing inside the aircraft and their breath is getting mixed before it enters the purification system. If the passengers around you are exhaling virus infected breaths, how are you protected? Masks do not protect you from virus entry into lungs.
On an assigned-seat flight, I ended up sitting next to a girl with a beautiful Himalayan/Siamese mix...She had the cat in a carrier under her seat...Irony is that of all the people to be assigned an adjacent seat on a large plane—it was me...I knew she had a cat because I had seen her in line—fingers crossed I would not end up next to her.
After I sat in my seat, my eyes and nose told me who I was sitting next to before I even really looked at her...I have cat allergies. Fortunately, I had Claritin, inhaler, etc. and promptly took some which alleviated most of the symptoms within a half-hour to an hour...
Point is the plane’s air filtration was not doing much for me...