My question
Do you think that they (scientists) said you could not contract COVID if you took the COVID vaccine?
Was in relation to the process of scientific enquiry and the papers/claims made by scientists generally. Reporting results and drawing conclusions in such papers are typically restricted to the hypothesis being tested and, where further, more speculative conclusions are stated, are often couched in less certainty, and point to further testing/ hypotheses.
As others here have pointed out - science is not a one-track path to the truth, rather science does not provide absolute proof, but rather evidence that supports or refutes a hypothesis. Absolute claims such as you could not contact COVID if you took the COVID vaccine are unlikely to be made by the scientists themselves who report on their studies and trials.
Fauci is a scientist. He was not directly involved in the COVID vaccine development but had a role in public communication and response to the pandemic. He is an infectious disease expert and has participated in many scientific studies of infectious diseases. If such a statement was made by him then it was stupid. However, I have found no such statement. Do not confuse related statements with the messages he may have made about safety or severity: One such report:
Dr. Anthony Fauci, on why individuals with the COVID-19 vaccine should still wear masks in public until the country achieves herd immunity.
Fauci explained that it is not clear how effective the current vaccines are at curbing the spread of the virus from an immunized person to others. In other words, a vaccine will prevent the recipient from getting sick, but that person may still carry the virus and expose those who have not received the vaccine.
Did Fauci make the statement that the vaccine will prevent the recipient getting sick? The tendency may be to interpret that no illness occurs, but it is not that. Some here obviously think that and try to deliberately misrepresent the position being stated. May be a form of TDS directed at Fauci?