By the way, for everyone else who - like me - doesn't have a NYT subscription and thus don't know what the above comment is talking about, the Washington Post has what looks like an equivalent version of the same story:
https://www.washingtonpost.com/health/2021/07/29/cdc-mask-gu...
Internal CDC documents have leaked. Here are some quotes from the report:
"It cites a combination of recently obtained, still-unpublished data from outbreak investigations and outside studies showing that vaccinated individuals infected with delta may be able to transmit the virus as easily as those who are unvaccinated. Vaccinated people infected with delta have measurable viral loads similar to those who are unvaccinated and infected with the variant."
"The breakthrough cases are to be expected, the CDC briefing states, and will probably rise as a proportion of all cases because there are so many more people vaccinated now. This echoes data seen from studies in other countries, including highly vaccinated Singapore, where 75 percent of new infections reportedly occur in people who are partially and fully vaccinated."
"The presentation highlights the daunting task the CDC faces. It must continue to emphasize the proven efficacy of the vaccines at preventing severe illness and death while acknowledging milder breakthrough infections may not be so rare after all, and that vaccinated individuals are transmitting the virus. The agency must move the goal posts of success in full public view."
There are some other points worth noting from the presentation:
1. The frequent and very US specific claim that "99% of hospitalizations are in the unvaccinated" isn't true. CDC stats show 15% of hospitalizations are from vaccinated people and the number is growing. Why are they claiming otherwise in public?
2. The confidential data is not really surprising, because it brings the USA into line with what every other country is seeing.
There's a good summary of some of the latest non-US data from UK and Israel here. Efficacy against infection and "mild illness" keeps falling:
https://swprs.org/covid-vaccines-the-good-the-bad-the-ugly/