The research I saw shows the viral load of vaccinated people is the same if not higher.

https://www.ucdavis.edu/health/covid-19/news/viral-loads-sim...

Do you have other references?

First, vaccinated folks clear the virus faster, so the overall time of infectiousness is lower. https://globalbiodefense.com/2021/12/04/vaccinated-people-cl...

Second, fewer vaccinated people have breakthrough infections in the first place, so overall spread is lowered because of vaccinations.

I can see that in theory, but when you look at the cases curve in the US pre and post-vaccination you can't really tell there has been a "huge" effect, I would even call that a failure, frankly if we had given everybody enough vitamin D to fix the significant average deficiencies, that would have a much more dramatic effect on reducing infection and spread. Maybe we could even have a vitamin D pass :P...

You’re not seeing how the delta variant would have spread in a fully unvaccinated population. Notice how the original variant and the more infectious alpha variant failed to thrive post-vaccine. There was some competition effect from delta but it isn’t as if one variant directly suppresses another. Delta would have ravaged the country without vaccination reducing its rate of spread.

Bulgaria has a very low vaccination rate (27%) and the curve doesn't look that much different from the US's: https://www.google.com/search?q=bulgaria+covid

It does seem better, but can we know for sure to what this can be attributed? Usually places that had an easier time in 2020 got worse this year, and vice-versa, which makes sense...

The Economist tracks excess deaths, which is a more accurate measure of how deadly COVID is, especially in places with iffy stats.

Bulgaria looks like reporting is not reliable: https://www.economist.com/graphic-detail/coronavirus-excess-...

US vaccination rate is not great, and will be patchy (some places quite well vaccinated, some well below average).

A better comparison would be Bulgaria to Portugal.