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Besides the 3-month-duration broadly effective antiviral prophylactics that Josh mentioned, I think that daily broadly antiviral prophylactics could also be promising if they could eventually become widespread consumer products. However, the science is still pretty nascent – at least for prophylaxis, I don't believe there is much human data at all, and I haven't seen anything I've seen reaches truly 24 h duration efficacy (which I'd see as a major barrier to consumer uptake).
Here are some links:
"PCANS", and its commercial product Profi nasal spray
INNA-051 ferret study, Phase 2 influenza challenge study (press release and more negative take)
"SHIELD"
I think transmission reduction hasn't been tested specifically, but anything that's localized to the upper respiratory tract and is prophylactic should theoretically reduce transmission as well.
Dan Watendorf at the Gates Foundation has said they've funded a few different companies that produce broadly effective antiviral prophylactics (e.g. a nasal spray that would keep you from getting colds, flus, and COVID for 3 months). He seemed to be optimistic about the technical solvability of the problem but pessimistic about a financing model that would make it viable (i.e. that transmission-reduction is not properly incentivized by the market)
Curious about this since "you're a lot less likely to get sick in winter" sounds like an extremely desirable OTC consumer product and one even employers might have incentives to support. Is it that the efficacy works on a population level by keeping R values down but isn't reliable enough at preventing symptoms on an individual level for consumers to believe in it?
I think that’s the idea but I also don’t know that many details
I think that if the broadly effective antiviral prophylactic was truly effective on an individual level, then there could be a reasonable market for it. But the market value would be based on its efficacy at protecting individuals, not on transmission reduction.
Which I think is fine - in the absence of specific incentives to make drugs that reduce transmission, a strategy that involves bringing transmission reduction "along for the ride" on otherwise already-valuable drugs makes sense to me.