This is a new trial of the Pfizer mRNA vaccine, which specifically examines its efficacy for stratified groups of elderly and non-elderly age groups, different dosages, and as a booster shot. The detals are listed at the link you provided under the heading “Study Description.” Phase 3 of the original trial, which led to the “emergency authorization,” were actually completed in Novenber 2020, not January 2021 as I first wrote.
“Estimated completion date May 2023
https://clinicaltrials.gov/ct2/show/NCT04368728“