Looks like really good news to me and probably explains the low death rate we've got (now). People are still getting ill but as ICU staff keep explaining it's the anti-vaxxers who end up ventilated.And what is this about then?
"Seropositivity estimates for N antibody will underestimate the proportion of the population previously infected due to (i) blood donors are potentially less likely to be exposed to natural infection than age matched individuals in the general population (ii) waning of the N antibody response over time and (iii) recent observations from UK Health Security Agency (UKHSA) surveillance data that N antibody levels appear to be lower in individuals who acquire infection following 2 doses of vaccination."
Page 23
Page 3
"Vaccine effectiveness
Several studies of vaccine effectiveness have been conducted in the UK which indicate that 2 doses of vaccine are between 65 and 95% effective at preventing symptomatic disease with COVID-19 with the Delta variant, with higher levels of protection against severe disease including hospitalisation and death. There is some evidence of waning of protection against infection and symptomatic disease over time, though protection against severe disease remains high in most groups at least 5 months after the second dose.
Population impact
The impact of the vaccination programme on the population is assessed by taking into account vaccine coverage, evidence on vaccine effectiveness and the latest COVID-19 disease surveillance indicators. Vaccine coverage tells us about the proportion of the population that have received 1 and 2 doses of COVID-19 vaccines. By 10 October 2021, the overall vaccine uptake in England for dose 1 was 65.5% and 60.4% for dose 2. In line with the programme rollout, coverage is highest in the oldest age groups. We present data on COVID-19 cases, hospitalisations and deaths by vaccination status. Based on antibody testing of blood donors, 98.0% of the adult population now have antibodies to COVID-19 from either infection or vaccination compared to 18.7% that have antibodies from infection alone"
As to your concern about waning N-antibody levels :
page 19 :
"Nucleoprotein (Roche N) assays only detect post-infection antibodies, whereas spike (Roche S) assays will detect both post-infection antibodies and vaccine-induced antibodies. Thus, changes in seropositivity for the Roche N assay reflect the effect of natural infection. Increases in seropositivity as measured by S antibody reflect both infection and vaccination."
Seems to be proof that the vaccine works as the vaccinated don't get infected.
Also from page 23 :
"Seropositivity estimates for S antibody in blood donors are likely to be higher than would be expected in the general population and this probably reflects the fact that donors are more likely to be vaccinated."