Question: What have we learned about the safety of flying?  Most of the articles I read seem to indicate that flying is just not that big of a risk because of the strong ventilation systems on planes. Is that just airlines trying to get us back to flying or is there independent verification for this science?

Answer:  We talked most recently about this issue in our Q&A of 7/1, which includes a cool diagram of airplane ventilation systems. We have more data now, so it’s worth revisiting the discussion.  First, let’s remind ourselves of the 3Cs– risk increases with closed spaces, crowded places, and close-contact settings.  The degree to which airplanes and airports meet these “high risk” criteria depends on the risk mitigation measures they implement. Flying becomes increasingly safe as airlines/airports implement more public health interventions (often called non-pharmaceutical interventions or NPIs). For airplanes:

• Risk from “closed spaces” is minimized because of the impressive air filtration/ventilation system used on board as well as comprehensive cleaning protocols;
• Risk from “crowded places” can be minimized by reducing passenger capacity.  This is a safety/revenue trade off and different airlines have made different calculations.  I’ve read that some airlines are moving back to full capacity;
• Risk from “close-contact settings” can be reduced by keeping passengers spaced apart (e.g. not filling the middle seat) and implementing mask mandates for all passengers.  Like the crowded places issue, this is a safety/revenue trade off of keeping passengers spaced and the decision/practice varies by airline.  Mask mandates are widely implemented, but enforcement seems to vary from airline to airline/aircraft to aircraft.

A recent report from Harvard’s Aviation Public Health Initiative found that when these risk mitigation measures are synergistically implemented, risk of transmission is low.  That said, we also have case studies of transmission events occurring on airplanes.  For example, earlier this month, CDC’s Emerging Infectious Diseases journal published Transmission of SARS-CoV 2 During Long-Haul Flight. Scientists investigated a cluster of cases among passengers on a 10-hour commercial flight, finding “Among the 16 persons in whom SARS-CoV-2 infection was detected, 12 (75%) were passengers seated in business class along with the only symptomatic person (attack rate 62%). Seating proximity was strongly associated with increased infection risk (risk ratio 7.3, 95% CI 1.2–46.2).”  The upshot is that transmission can absolutely occur on airplanes, but the risk is minimized as more NPIs are implemented and enforced.  I suggest that before booking a flight, you research which airlines are implementing the most NPIs.  Relying solely on good ventilation is not going to cut it!