Modern aircraft, ie since the DC8 or 707s, circulate air across the cabin and filter the air using HEPA technology (which captures viruses). Said filters are cleaned and/or replaced on a regular schedule and this is logged. The filters used are certified for use on that aircraft type/model. and not just picked up at the ASDA/Walmart.
Since the airflow is across the cabin you are unlikely to be exposed from more than a row forward and a row back. Of course if an infected person is sitting next to you you are going to catch it.
Viruses are everywhere and many people become ill while travelling. . If you catch a bug it is as likely you picked it up in a queue to check in, or for security - or perhaps in the taxi on the way to the airport, none of which have air filtered as in a commercial aircraft.