I was very interested at the results of my spouse's antibody test! It was negative, and we thought for sure she had antibodies from infection. I have no scientific evidence, but she has genetic abnormalities in certain blood proteins, and I wonder if that assists with her resisting the infection!
antibodies are only measurable for a short time; long-term ability to defend is "learned" by the immune system but not measurable in any ordinary way; here in California coastal area there is a lot of social pressure about vaccination. Random people still insist that vaccination is important for healthy adults and sometimes under-18.