I came back from Vietnam about four weeks ago with Thai airways via Bangkok; the cabin was sprayed before take-off (not sure what with, it smelt a bit like standard household air freshener to be honest).
I have seen this before during nasty insect season, but we were a bit early for that.
Cabin crew wore cotton surgical masks except for meal / drinks service, which all seemed a bit pointless. I guess the current business Guru's would call it "Best efforts".
Short answer - nobody knows for sure. Keep personal hygiene up to scratch, clean what you can with steri-wipes, but you can't stop public life!