- https://www.cnn.com/2021/09/22/health/cdc-vaccine-advisers-b...
- https://www.cnn.com/2021/08/24/health/us-coronavirus-tuesday...
- https://www.healthline.com/health-news/heres-how-well-covid-...
- https://www.nature.com/articles/d41586-021-02261-8
- https://www.cnbc.com/2021/10/04/pfizer-covid-vaccine-protect...
- https://www.cnbc.com/2021/10/04/pfizer-covid-vaccine-protect...
What you're seeing is two factors combined, first delta being more infectious. But delta only became widespread in many places in ~July, so solid data on how it affected infectiousness took until August or September. And second, the vaccine's effectiveness wanes over time, but again, this takes time to detect. So it is simultaneously true that in January of this year, the vaccines were in some cases 90% effective at reducing infection, but are now 40-60% effective (note that this still *halves the r0, which is significant).
And those numbers have been communicated in the mainstream media and via official channels like the CDC (although the CDC has never posted efficiency numbers: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effective..., see that this was last updated in May). Perhaps you weren't paying attention though.