>>Here's my issue with that (and this is not directed towards you)...the definition of "effective". I'm not challenging the 39 and 42 numbers - just want the context is.
>>If it's 39% effective against acquiring enough viral load that I don't test positive, I'm not necessarily scared. Since the vaccine still provides much higher protection against serious illness, that's what's more important to me.

For vaccines, "efficacy" means risk reduction measured by controlled study versus an untreated control group. So Pfizer's 95% efficacy doesn't mean that for every 100 exposed vaccinated people, only 5 get infected; it means that after vaccination you have 1/20 of the control group risk of infection.

"Effectiveness" is the level of protection in real life once the treatment is deployed. For classical vaccines like MMR it's very similar to efficacy at around 97% which has remained reliable for decades now, but for entirely new C19 vaccines the only way to determine efficiency is to deploy and watch.

As of August 2021: while Pfizer had the highest 95% efficacy, for delta it can have only 39% effectiveness meaning your risk of infection is 61% of an unvaccinated person's risk; whereas Moderna with 94% efficacy can have 76% delta effectiveness.

Who knows what will happen with upcoming variants. When people sound absolutely certain on any of this stuff, it's worth considering that "the more you know, the more you realize you don't know" especially when the bug continues to mutate.

>>When I hear a news person say, "X percent effective" without qualifying, it is clear to me that the news person (or whoever wrote the news copy) doesn't give a GGDSFF about context - they just feel morally superior that they can quote a number.

Yes. Between themselves doctors have to rely on medical jargon to convey complex scenarios efficiently (using the lay definition ;-) ) but anybody who ever practiced is comfortable explaining- and it's not as if vaccine efficiency is rocket science any more than wearing a mask properly is rocket science, which the talking heads also resist explaining when they exhort people to wear them.

>>There are days when I think this government has outlawed denominators.

See if you can find the upcoming Mayo paper reviewing effectiveness of Pfizer versus Moderna. They have quite a good "1000 person days" type denominator to demonstrate changing infectiousness and risk over time independent of cohort size or big scary numbers.