Non-pandemic, I am a frequent flyer and always take insulin with me.
I have always been told to ensure I have a letter from my doctor explaining that I need to keep it (and the needles) with me at all times. It has been very rare that I have been asked to produce this letter but I have and, given the alternative could be a refusal to fly, I always keep the letter with my passport.
My letter is generic so I can reuse it (it getting a bit scruffy now) and was provided by my endo - GPs often charge for it.
I have flown throughout Europe, US and some Asian countries and been questioned in US and Europe (never Asia but that may be coincidence).
On the plus side, I do get to have a little frisson of (slightly evil fun when I check in.
Check-in desk: "Do you have any sharp items in your luggage?"
Me: "Yes"
C-iD: (look of panic, unsure what to say next)
Me: (silence)
CiD: (panicked look continues)
Me: "I have diabetes"
CiD: (look of relief) "No problem, that's fine, Tell the boarding crew as you get on the flight."
To be honest, I used to tell the boarding crew and they would look at me blankly so I stopped telling them. It's not any of their business and I would prefer to keep everything with me.
A couple of other points about flying with insulin
- ALWAYS keep you insulin in your hand luggage. Your checked in luggage may go awry and it may reach low temperatures in the hold which can damage insulin. My preference is to not put it in the plane fridge as I am likely to forget it. I want it with me.
- Do not leave hypo treatments in the overhead locker. From personal experience I can tell you it is embarrassing (and potentially dangerous) having to get up to treat a hypo when the seat belt signs are on.