The FDA recently approved the T-Detect COVID test to check memory T cell response.

https://www.fda.gov/news-events/press-announcements/coronavi...

I did a T-Detect test. Their website states "A recent study demonstrated 95% of patients tested positive for T cells up to five months after a confirmed positive PCR test.1 Clinically validated data for T-Detect COVID performance beyond five months is not available yet." but it has stated this for months now.

I assume they are tracking how long their test detects T cells in subjects who had confirmed infections and hope they will provide public updates on this more frequently because "up to 5 months" is of limited value to people like me who were interested in knowing if they had the virus back in the earliest days of the pandemic.

Presumably the 5-month duration was based on the date of their 2020 submission for FDA EUA approval, relative to the earliest date of infection of their test subjects. If those early test subjects are participating in the ongoing trial of T-Detect, it's now probably a year since their infection & recovery. Hopefully we'll see a longer duration in their next FDA submission.

yes this is a good thing, the virus[sars2] has a feww features that allow partial stealth, and has accumulated variations that contribute to possible immune evasion.

this should not be taken casually, and perturberance of memory immunity should it occur would be a variant profile of high concern.

Sorry I’m not quite sure I follow. You’re saying antibodies are the “quick and easy” way to measure whether a person’s body is (correctly) reacting to the vaccine. So when someone has antibodies soon after vaccination it’s a sign it’s worked, but the antibodies dissipating isn’t necessarily a sign a person no longer has immunity? But since testing for antibodies is the only feasible test available to measure immune response in response to the vaccine it’s become conflated with actual immunity?

So someone could (in theory) get the vaccine, have tons of antibodies 6 weeks later, then have greatly reduced antibodies and it doesn’t tell us anything about whether or how much immunity that person will have if they’re infected?

Someone will have tons of antibodies 4-6 weeks later and then experience a drop off. Especially if you’re measuring from the first vaccine dose.

This is literally how the Adaptive immune system works.

Initial adaptive response, production of IgM, Vdj recombination, class switching and global proliferation (especially in the face of a repeated antigen insult), followed by a tone down of B cells as the memory effect is preserved and the antibody titre falls back (antibodies have a half life of 3-4 weeks).

Because (at least currently) the antibody response in humans is non-sterilising (talk of boosters to generate IgA abound, along with a more specific Delta variant vaccine may change this) you can’t equate a titre in humans yet with a ‘level’ of immunity

you as well understand at a deeper level

More or less. There's cells that remember how to make the antibodies, speeding up the response to a second exposure even long after the initial exposure.

Having lots of antibodies when exposed can maybe prevent infection or lessen severity, so it isn't a complete non-concern that they fade.

you understand the concept in a practical form

you seem to understand it correctly, the level of >protection< may be inferred by observing titre of antibodies, the strength of immune response may be inferred by observing increase of titre after challenge by pathogen.

the durability of immunity may be inferred by observing the increased response to challenge over points in time.

Your right, but anybody else making this argument up until now in defense of natural immunity got ignored or ridiculed.