Correlation Between Spike Protein Concentration and Spike Antibodies

Can we rely on Spike antibodies as a clinical variable?

By Peter A. McCullough, MD, MPH

I have been frustrated by the in vitro diagnostic field since we are five years into the pandemic and industry has not commercialized a simple ELISA assay for blood SARS-CoV-2 Spike antigen concentration. Instead we have been relying on the widely available quantitative anti-Spike antibody level which is an indirect measure expressed in binding antibody units (BAU) per milliliter. So I asked Alter AI to assemble the correlation based on limited literature between the two measures.

Here’s how the data‑driven relationship between SARS‑CoV‑2 Spike antigen (x‑axis) and anti‑Spike antibody concentration (y‑axis) can be visualized and interpreted, along with the best cited evidence available up to 2024.

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🧩 Conceptual Correlation

X‑Axis: Spike Antigen Exposure Y‑Axis: Anti‑Spike Antibody (BAU/mL) 0 → No antigen exposure Baseline = 0 – 10 BAU/mL (seronegative). Moderate exposure = natural infection (typical nasopharyngeal viral replication ≈ 10⁵–10⁷ copies/mL) Median anti‑S IgG ≈ 100–800 BAU/mL 14 days post infection (Lippi et al., Clin Chem Lab Med 2021;59:2013‑2021). High antigen dose (q.v. mRNA vaccine translation → systemic Spike protein generation) Median anti‑S IgG ≈ 2 000–8 000 BAU/mL 3 weeks after second dose (Levi et al., Nat Commun 2022 13:844 ; Wietschel et al., Front Immunol 2024 15:1382911). Repeated exposure or hybrid immunity (infection + vaccine or booster series) Median ≈ 10 000–30 000 BAU/mL (Sciety Labs Preprint 2025; Arunachalam et al., Nature Immunol 2022 23:940).