Just viewed an interesting YouTube video: "Why Is My Serology Negative But I had Symptoms?"

Apparently very common. There are a lot of people who tested positive by PCR, but never develop antibodies. One theory is that their innate immune system cleared the virus before their adaptive immune system got around to making antibodies. Antibody production actually takes more than 10 days, and if your mild infection only lasts 5 days antibody never happens.

He showed a preprint of a study that found some people with symptoms who had positive PCR tests, and then some of their family members who did get symptoms but were never tested. Hardly any of them had antibodies, but when they tested their T-cells against SARS-COV2 antigens, they were all activated. This is the path in the immune system that is quicker and does not make circulating antibodies. It is also the path that does not lead to memory B-cells.

But their T-cells were still testing as activated by SARS-COV2 80 days after their first symptoms. So this is a form of immunity. Anyway, it seems that people who have mild or asymptomatic infections will often not get a positive antibody test. (Like me.) It's kind of reassuring to know my responses to the virus are not unusual.

Of course, there are complications: Some vaccine guys say a good vaccine will have antibodies against several virus proteins, not just spike protein. Moderna is "spike only". Imperial College is quite like Moderna, but presents four different virus proteins (including spike). And what if you have antibodies against one or more of those other proteins, but not spike? Would you fail a very specific spike antibody test, but still be immune? If some of those other proteins were also in other corona viruses that circulated as common colds, could cold victims have partial immunity to SARS-COV2? Is that why kids usually don't get it, but a few die?

Vaccine production is tricky: Making antibodies against multiple pathogen proteins is good (because of viral mutation), but you have to make sure you don't make antibodies to something that is a normal part of the human body. The result would be an artificial autoimmune disease and possibly death.