Ripline
I started a thread on same subject (NOT helium) in
JetBlast this morning
We actually had the same idea about some human beings
Throuble is the vaccine does not affect gas production, it merely reduces its methane contents (and methane is odourless)
About nitrogen : big warehouses are now using reduced-oxygen-partial-pressure (or increase nitrogen if you put it the other way around) for fire prevention. Take a look
here especially at the video, quite impressive (just for information - I'm not affiliated with them)