But antibodies aren't the only thing that matters; focusing only on antibody levels without acknowledging that you only care about antibody levels _as a proxy f

But antibodies aren't the only thing that matters; focusing only on antibody levels without acknowledging that you only care about antibody levels _as a proxy for protection_ is the error I talked about in my comment. There are Memory T cells and Memory B cells that last for decades. So if these cells were able to fend off the virus by themselves, you could have zero antibodies and be fine. Some possibly useful articles: * https://en.wikipedia.org/wiki/Correlates_of_immunity https://en.wikipedia.org/wiki/Correlates_of_immunity * https://en.wikipedia.org/wiki/Memory_B_cell https://en.wikipedia.org/wiki/Memory_B_cell