Table 1.

In bold are antibody responses that were used to determine a broad, conservative range of peak S1 and S1-RBD IgG binding antibody values post-vaccination that may indicate a potential binding antibody CoP target, 1372–3803 BAU/mL, in largely immunocompetent populations and a potential booster target range for the immunocompromised and elderly. However, the high end of this range is from two studies using S1 IgG, rather than S1-RBD IgG, and it is likely that the higher values observed are in part due to more measurable antibodies against the entire S1 subunit than S1-RBD alone. If we only focus on S1-RBD IgG values the CoP range narrows to 1372–2744 BAU/mL and covers both mRNA vaccine (i.e., Pfizer and Moderna) and recombinant protein vaccine (i.e., Novavax) approaches. Additionally, some binding antibody responses were reported as median values and others as mean values, so the S1-RBD IgG range indicated would slightly shift if all were mean or median values. Oxford/AstraZeneca (AZD1222), Janssen, and Sputnik viral vector vaccine responses were excluded as they appear to produce lower responses than mRNA vaccines. Peak antibody responses post-vaccination series (i.e., 1 or 2 doses as specified by manufacturer) in largely immunocompetent populations extracted from clinical trials and research studies.

Antibody Assay (Source)	N (Received Vaccine)	Antibody Level or Titer	Study	Vaccine	Doses	Percent Efficacy	Clinical Endpoint Measure	Days Post Second Dose	Dominant Variant at Time of Study	Population Studied
Anti-spike IgG (MSD Diagnostics)	1051	1890 BAU/mL † GMC Ω (95% CI: 1499 to 2465)	COVE [22]	mRNA-1273 (Moderna)	2	90%	Symptomatic COVID-19	Median 28	Alpha	General; 47% female, 34% > 65 y/o, 40% at high risk for severe COVID-19, 54% non-white. Infection naive at baseline
Anti-S1RBD IgG (MSD Diagnostics)		2744 BAU/mL † GMC Ω (95% CI: 2056 to 3664)
Pseudovirus Neutralization assay		160 IU50/mL ∞ GMC Ω [95% CI: 170 to 220]
Anti-spike IgG (MSD Diagnostics)	1155	264 BAU/mL † GMC Ω (95% CI: 108 to 806)	COV002 [23]	ChAdOx1 nCoV-19 (AZD1222)	2	80%	Primary symptomatic COVID-19	28	Alpha	General; 57.9% female, 74.1% < 55 y/o, 24.9% at high risk for severe COVID-19, 92.3% white. Infection naive at baseline
Anti-S1RBD IgG (MSD Diagnostics)	1155	506 BAU/mL † Median (95% CI: 135 to NC ‡ [beyond data range])
Pseudovirus Neutralization antibodies	828	26 IU50/mL GMC Ω (95% CI: NC ‡ to NC ‡)
Live-Virus Neutralization antibodies	412	247 normalized neutralization titer (NF50) (95% CI: 101 to NC ‡)
Anti-spike IgG (MSD Diagnostics)	826	238 BAU/mL 97.5th percentile	ENSEMBLE [25]	Ad26.COV2.S (Janssen)	1	89%	Moderate to severe-critical COVID-19	29	Alpha	General; 44.8% female, 50.4% ≥ 60 y/o, 51.7% at high risk for severe COVID-19, 49.3% non-white. Infection naive at baseline
Anti-S1RBD IgG (MSD Diagnostics)		173 BAU/mL 97.5th percentile
Pseudovirus Neutralization Assay		96.3 IU50/mL ∞ 97.5th percentile
Anti-spike IgG (MSD Diagnostics) Anti-S1RBD IgG (MSD Diagnostics)	19,996	1552 BAU/mL † GMC Ω (95% CI: 1407 to 1713) 2123 BAU/mL † GMC Ω (95% CI: 1904 to 2369)	PREVENT-19 [24,26,27]	NVX-CoV2373 (Novavax)	2	87.7%	Symptomatic COVID-19	35	Primarily Alpha	General; 46.7% female, 46.7% ≥ 65 y/o, 49.7% at high risk for severe COVID-19, 42.5% non-white. Infection naive at baseline
Pseudovirus Neutralization Assay		461 IU50/mL ∞ GMC Ω (95% CI: 404 to 526)
Anti-S1RBD IgG (Abbott Diagnostics)	52	2018.0 BAU/mL † Median	Deeba et al., 2022 [28]	BNT162b2 (Pfizer)	2	N/A	N/A	~21	Omicron (BA.2)	Healthcare professionals in Cypress
	45	182.1 BAU/mL Median		ChAdOx1 nCoV-19 (AZD1222)	2
Anti-S1RBD IgG (In-house ELISA)	86	1209 BAU/mL † Mean (in previously infected) or >694 BAU/mL † (correlated to excellent neutralizing activity)	Claro et al., 2022 [29]	Sputnik	2	91% in infection naive; 100% in previously infected	Good to excellent neutralizing activity as defined by WHO standardized neutralizing antibody response of 100–400 or greater IU/mL	42	Alpha (B.1.17)	Healthcare professionals in Venezuela
Anti-S1RBD IgG (Abbott Diagnostics)	1343	1432 BAU/mL   † Median	Bordi et al., 2022 [30]	BNT162b2 (Pfizer)	2	N/A	N/A	~30	Delta	Healthcare professionals in Italy
Anti-S1RBD IgG (Snibe Co., MAGLUMI)	2248	1372 BAU/mL   † Median	Lo Sasso et al., 2021 [31]	BNT162b2 (Pfizer)	2	N/A	N/A	10–20	Mainly Alpha	Outpatients presenting for blood draw in Italy
Anti-S1 IgG (Euroimmun Anti-SARS-CoV-2-QuantiVac-ELISA)	93 (age < 60 y/o)	3702 BAU/mL   † Mean	Muller et al., 2021 [32]	BNT162b2 (Pfizer)	2			17	Mainly Alpha	Infection naive adults (younger and older elderly populations) from nursing home facilities in Germany
	83 (age > 80 y/o)	1332 BAU/mL † Mean
In-house PRNT (neutralization) assay	93 (age < 60 y/o)	ID50 ∗: 97.8%
	83 (age > 80 y/o)	ID50 ∗: 68.7%
Anti-S1 IgG (Euroimmun Anti-SARS-CoV-2-QuantiVac-ELISA)	107 out of 263	2478 BAU/mL † Mean (before Omicron BA.1/2 breakthrough)	Kajanova et al., 2023 [33]	Several vaccines	At least 2 (or series completed)		No breakthrough infection during period studied	N/A	Omicron BA.1/2	Healthy adult volunteers; 76% female, 24% male; median age 45 y/o, in Slovakia with previous vaccination series completed
	152 out of 263	3803 BAU/mL   † Mean (before NO Omicron BA.1/2 breakthrough)				100%
	141 out of 263	>6201.5 BAU/mL † (upper most quartile of responses most likely to avoid breakthrough infection)

† BAU/mL = binding antibody units/milliliter (WHO standardized); Ω GMC = geometric mean concentration; ∞ IU₅₀/mL = concentration at which 50% neutralization is observed expressed in international units (IU) per milliliter.; ‡ NC = not computed; ∗ ID50 = inhibitory dilution at which 50% neutralization is observed.