There is more to the immune system than antibody production. A lot of the focus is on antibody production, because it is easy to measure. T Cell responses, for instance, can be very durable for coronaviruses--for instance, people who recovered from SARS in 2003 still have a T Cell response when exposed to a protein from that virus (https://blogs.sciencemag.org/pipeline/archives/2020/07/15/ne...).

The Oxford/AZ (https://blogs.sciencemag.org/pipeline/archives/2020/07/20/ne...) and the Pfizer team (https://blogs.sciencemag.org/pipeline/archives/2020/07/20/mo...) have both reported T Cell responses induced by their vaccines.

Robus T Cell responses should be protective, but we are still mapping that out for SARS-CoV-2 (https://blogs.sciencemag.org/pipeline/archives/2020/07/15/ne...).