Ah thank you Pinkman for a more medical scientific explanation. I stand corrected on the source of the pressure moving the "virus laden particles back down", and apologise to the ECS designers I have offended.
The air pressure in the cabin varies throughout the flight though. From Kelly at al (reference below):
It is a commonly held belief that cabin air pressure is maintained at a constant level during long-haul commercial flights. A recent British Medical Journal editorial included the statement that cabin pressure is maintained at the equivalent of 8000 ft (2440 m) in altitude. As demonstrated in this study, cabin air pressure is not constant and decreases as aircraft cruise at higher altitudes in the latter part of long sectors.
Their figure 1 below is their measurement of the variation of cabin air pressure during one flight shows the scope for "grunting and snorting" responses:
This is not a criticism of the aircraft engineering, and it is important to note that even when at their highest cruising altitudes, the Boeing 747–400 aircraft studied provided cabin air pressure conditions that comfortably exceeded the current regulatory standards.
Their figure 2 is a summary of the relationship between aircraft altitude and cabin conditions taken from 45 flights, and shows that the magnitude of the pressure changes:
REF: Directly measured cabin pressure conditions during Boeing 747–400
commercial aircraft flights. Paul T. KELLY, Leigh M. SECCOMBE, Peter G. ROGERS AND Matthew J. PETERS. Respirology (2007) 12, 511–515