That makes sense and might explain the increased viral levels in sneezes - the narsty stuff just builds up, viruses with it, until a sneeze helps expel some of the excess, which would normally drain off.

Your point about the closed environment is a good one - no outside bugs - and I would add that most of the astronauts, if not all, are probably in much better health than the average bear, and so much more unlikely to bring any odd bugs into space with them, imo, that depressed immune systems might have difficulty fending off.

Come to think of it, isn't the commerical, off-the-self decongestant Contac a derivitive of the space program, where it was formulated early on to give astronauts some relief from their sinus problems?

The bottom line here, I think, is that there's still a lot of work to do in space medicine before we are ready for really long space voyages.

sp