It has been my understanding thus far that detectable B cell antibodies develop in 99% of Covid carriers, regardless of symptoms. They make take 14 days from onset, they may disappear, and the assays attempting to detect them may be imperfect, but at some point they are always there.
It is still hypothetically possible a portion of the population is genetically less susceptible (immune), similar to how Children are less susceptible, and suggested by the tightly confined spaces like cruise and military ships were typically 40% of the population did not have detectable PCR Positive nose swabs, irregular CT lung scans, or B-Cell antibodies. However, it also possible the exposure was not uniform across the ships, especially if we assume only a handful of super spreaders are responsible for directly infecting the other passengers, and most Covid carriers are not contagious most of the time.
However, claims have been emerging about T-Cell immunity resulting from Covid infections without any present B-Cell antibodies. This T cell reaction can be detected by simulating a Covid infection in the blood sample, in a complicated assay described here -
https://bio-protocol.org/e2302.
Can anybody shed more light on this topic?
Exhibit A is a NY study of 1343 symptomatic PCR-Positive Covid carriers, all but 3 of whom developed B cell antibodies
https://www.medrxiv.org/content/10.1101/2020.04.30.20085613v1Exhibit B is a tiny French study that examined 9 Covid patients, 8 household contacts, and a few old blood samples for control. The samples were drawn 47 days after infection, so it's possible antibodies simply weren't there anymore. 6 out of 8 of the studies contacts had some symptoms, but none tested positive on PCR swab tests. We know those tests are only 70% accurate, so it doesn't tell us much.
They found 6 out of 8 contacts all had a unique T cell response that was not present in any of the control samples that were not exposed to Covid. Although it was still different than the T cell response seen in the 9 confirmed patients.
The study appears to contradict itself, at one point stating 6/8 contacts exhibited symptoms (4 fever, 3 cough) [Page 6, line 130], but then stating 5/6 contacts with T cell responses were asymptomatic [Page 8, line 168]
https://www.medrxiv.org/content/10.1101/2020.06.21.20132449v1I will continue posting more information as I research it.