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."
Person A >Transmission> Person B >Transmission> Person C
Person A >Transmission> Person B (Prevention)
So the research you are referring to is in regards to other variants of sars-cov2
"A COVID-19 Vaccine May Be Only 50% Effective. Is That Good Enough?"
https://www.npr.org/sections/health-shots/2020/09/12/9119879...
August 7, 2020:
"Fauci says COVID-19 vaccine may only be 50 percent effective"
https://nypost.com/2020/08/07/fauci-says-covid-19-vaccine-ma...
https://dictionary.cambridge.org/dictionary/english/prevent?...
If I am reading correctly (but do correct me if I am wrong because I am not 100% certain), only symptomatic cases are counted. Hence, it is quite possible for the vaccine to stop the symptoms, but not the transmission between individuals.
[1] https://www.nejm.org/doi/suppl/10.1056/NEJMoa2034577/suppl_f...
"A total of 43,548 participants underwent randomization, of whom 43,448 received injections: 21,720 with BNT162b2 and 21,728 with placebo. There were 8 cases of Covid-19 with onset at least 7 days after the second dose among participants assigned to receive BNT162b2 and 162 cases among those assigned to placebo; BNT162b2 was 95% effective in preventing Covid-19 (95% credible interval, 90.3 to 97.6). Similar vaccine efficacy (generally 90 to 100%) was observed across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and the presence of coexisting conditions. Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a BNT162b2 recipient. The safety profile of BNT162b2 was characterized by short-term, mild-to-moderate pain at the injection site, fatigue, and headache. The incidence of serious adverse events was low and was similar in the vaccine and placebo groups." https://www.nejm.org/doi/full/10.1056/nejmoa2034577
Maybe this is legalese, but I am pretty sure your average Joe online, that reads all kind of weird things on Facebook or other places, won't understand the subtleties of this language.