This is us! BART train cars' HVAC units has always recycled all indoor air at around every 70 seconds. We upgraded all HVAC filters to a stronger MERV-14 filter last year.
When you ride BART, air inside a train car is replaced more frequently than at a grocery store or office. twitter.com/sri_srikrishna…
The 1st report of an HLA association with antibody response following Covid vaccines and risk of breakthrough infections
https://nature.com/articles/s41591-022-02078-6…@NatureMedicine