This quote doesn't say anything about whether the vaccine reduces transmission of the virus. Even large phase-3 studies like the ones done for the COVID vaccines don't have anywhere near the statistical power to determine this. Now we have epidemiological data that shows a clear reduction in transmission, but not as much as the vaccines protect against serious disease.

Here is another quote from the same paper [1]: "This report includes 2 months of follow-up after the second dose of vaccine for half the trial participants and up to 14 weeks’ maximum follow-up for a smaller subset. Therefore, both the occurrence of adverse events more than 2 to 3.5 months after the second dose and more comprehensive information on the duration of protection remain to be determined."

[1] https://www.nejm.org/doi/full/10.1056/nejmoa2034577