"If the antibodies are falling . . . the prevalence of the virus in the population is falling"

SAGE, the Scientific Advisory Group for Emergencies, took the view that because SARS COV2 was a new virus that they believed that there wouldn't be any immunity at all in the population  SARS 2 is 80% similar to another virus you may have heard of--SARS that moved around the world a bit in 2003.  There are four (4) common cold-causing coronaviruses, and that I think that quite a lot of the population had been exposed to one of those viruses and probably have substantial protective immunity.  To explain why I was so confident, everybody knows the story of Edward Jenner, vaccination, and the story of cowpox and smallpox.  Milkmaids were exposed to a more benign form of smallpox called cowpox, which did not leave their skin scarred.  "If it's cowpox that saves the fair maid, he reasoned that giving a healthy person a vaccination, he would be able to protect them against smallpox.  Vaccination comes from vacca, the Latin name for cow.  So we are really familiar with the principle of cross immunization.  The vulnerable people in care homes, there's an awareness that caregivers are really careful and using PPE and so on.  But that's only going to go so far in a hothouse environment where people are pretty close together in a care home.  So they questioned Once one or two people got the coronavirus in a care home, why wouldn't almost everyone get infected?  And, of course, the truth is they didn't.  One interpretation of that distinction is that a large proportion of the people in the care homes had pro-apt immunity.  

Big story in the media recently (September 2020) was that a percentage of the population with antibodies against the virus, 4.4%, was falling.  This was cast as a concern that immunity to SARS CO2 doesn't last very long.  Anyone with knowledge of immunity would simply reject that.  That's not the way that immunity to the virus works: that would be T-cells.  So if the antibodies 

Immunity to the virus is created by T-cells, not by antibodies.  If the antibodies are falling, gradually over time which they have from spring to present, the only plausive explanation is that the prevalence of the virus in the population is falling and that's why the production of antibodies in the body gradually subsides.   

Less than 40% of the population was susceptible.  Even theoretical, epidemiologists will tell you that that's too small a number to support and consolidate a growing outbreak.  Community immunity: herd immunity.  So when SAGE says that