Thread by @federicolois

[1/n] While radical my current working hypothesis is that HIT is probably higher than what Oxford models suggest, even though we arrive at the same seroprevalence for cases curve concavity change. cc @MLevitt_NP2013

[2/n] I postulate that the observation of 15%-25% range for curve concavity is actually a measurement artifact that is not reflecting the actual seroprevalence at the population level.

[3/n] Rationale: Antibody level studies have 2 sources of error, one is calibration over clinical cases which affects the actual on the field sensitivity. Even the best assays will underestimate prevalence.

[4/n] But, the most relevant source of error is the dynamics of the immune response. Nature paper suggests that antibody levels fade quickly. nature.com/articles/s4159…

[5/n] The introduction of the time variable after the initial fast growth stage and the delay caused by interventions like using masks and hygiene would push the equation toward a steady-state

[6/n] where new population enters into the potentially measurable positive universe, while at the same time other fraction of the population gets out becoming seronegative.

[7/n] So you may ask, why we have seen then Argentinian slums with 55% seroprevalence medrxiv.org/content/10.110…, or Brooklyn at 45% medrxiv.org/content/10.110… .

[8/n] The reason is that in those places, it happened fast (unchecked), and we measured at the proper time before antibody fading would have a measurable impact.

[9/n] I also postulate that after you arrive at the 'real' concavity change on a geographical location (some countries were too successful in containing or delaying) what we are watching is a phase shift into seasonal behavior.

[10/n] Again, this is a working hypothesis that still has a few data holes (because it is too early) but so far seroprevalence data points are in agreement. The canary in the coal mine for me is the Geneva longitudinal study.

[11/n] Another source of strengthening of this hypothesis would be to rerun that Argentinian slums and Brooklyn where the prediction is that you will go way below 20% in between 4-6 months.