He is vaccinated. He's been vaccinated since April. Breakthrough infections are a thing. He's also concerned about recent data from Israel about waning efficacy. He'd get a booster shot today if he could get it.
Also thank you for what I presume is you insuinuating by putting "friend of yours" in quotes that you think I'm talking about myself. I've been vaccinated since April and I have been a lot more careful about this virus than at least probably 90% of the people out there, at least in the US. I still wear masks outside the house and avoid going indoors very often (I didn't do it at all until I was vaccinated).
Hell, I wore masks on hiking trails outdoors while holding my breath when walking past others on the trail back in 2020, which was probably overkill in retrospect. I also only had food delivered, never even going through the drive thru, and didn't order anything that couldn't be heated in the microwave for 3 minutes to try to kill the virus since it was unclear whether it transmitted via surfaces back then (so no sushi, sandwiches, salads, ice cream, iced coffee, etc).
Personally I wouldn't try to hunt down some of these alternative drugs, which I'm pretty skeptical of, but there seems to have been some mixed data on this one and I can at least understand why someone might want to give it a shot in reasonable and proven to be safe doses, especially if they have no choice but to be surrounded by it all day long (I work from home, my risk at work is nonexistent).
