Ryhog is 100% correct (no surprise there). People in the clinical trials continue to be studied, and by that I mean have their blood drawn periodically to check on the level of antibodies in the blood. These trials have been going on for much longer than six months, and there is no indication that immunity has decreased significantly (if at all) to date. If you are going to opine on the science, it would be good to have some actual scientific support. Otherwise, it's just BS and noise.
For example, here is some info regarding the Pfizer trial: The Phase 3 clinical trial of the vaccine began on July 27, 2020 and has enrolled 43,661 participants to date, 41,135 of whom have received a second dose of the vaccine candidate as of November 13, 2020. Approximately 42% of global participants and 30% of U.S. participants have racially and ethnically diverse backgrounds, and 41% of global and 45% of U.S. participants are 56-85 years of age.
So the Pfizer Phase 3 trial began almost exactly a year ago. These people are still being followed, and having their blood checked for antibody levels.