Antibody Response to Symptomatic Infection With SARS-CoV-2 Omicron Variant Viruses, December 2021-June 2022.

We describe humoral immune responses in 105 ambulatory patients with laboratory-confirmed SARS-CoV-2 Omicron variant infection. In dried blood spot (DBS) collected within 5 days of illness onset and during convalescence, we measured binding antibody (bAb) against ancestral spike protein receptor binding domain (RBD) and nucleocapsid (N) protein using a commercial multiplex bead assay. Geometric mean bAb concentrations against RBD increased by a factor of 2.5 from 1258 to 3189 units/mL and by a factor of 47 against N protein from 5.5 to 259 units/mL between acute illness and convalescence; lower concentrations were associated with greater geometric mean ratios. Paired DBS specimens may be used to evaluate humoral response to SARS-CoV-2 infection.

Anti-SARS-CoV-2 Antibody Levels Associated with COVID-19 Protection in Outpatients Tested for SARS-CoV-2, US Flu VE Network, October 2021-June 2022.

BACKGROUND: We assessed associations between binding antibody (bAb) concentration <5 days of symptom onset and testing positive for COVID-19 among patients in a test-negative study. METHODS: From October 2021─June 2022, study sites in seven states enrolled patients aged ≥6 months presenting with acute respiratory illness. Respiratory specimens were tested for SARS-CoV-2. In blood specimens, we measured concentrations of anti-SARS-CoV-2 antibodies against the ancestral strain spike protein receptor binding domain (RBD) and nucleocapsid (N) antigens in standardized binding antibody units (BAU/mL). Percent change in odds of COVID-19 by increasing anti-RBD bAb was estimated using logistic regression as (1-adjusted odds ratio of COVID-19)x100, adjusting for COVID-19 mRNA vaccine doses, age, site, and high-risk exposure. RESULTS: Out of 2,018 symptomatic patients, 662 (33%) tested positive for acute SARS-CoV-2 infection. Geometric mean RBD bAb were lower among COVID-19 cases than SARS-CoV-2 test-negative patients during both the Delta-predominant (112 vs. 498 BAU/mL) and Omicron-predominant (823 vs. 1,189 BAU/mL) periods. Acute phase ancestral spike RBD bAb associated with 50% lower odds of COVID-19 were 1,968 BAU/mL against Delta and 3,375 BAU/mL against Omicron; thresholds may differ in other laboratories. CONCLUSION: During acute illness, antibody concentrations against ancestral spike RBD were associated with protection against COVID-19.

Antibody response to symptomatic infection with SARS-CoV-2 Omicron variant viruses, December 2021-June 2022.

To describe humoral immune responses to symptomatic SARS-CoV-2 infection, we assessed immunoglobulin G binding antibody levels using a commercial multiplex bead assay against SARS-CoV-2 ancestral spike protein receptor binding domain (RBD) and nucleocapsid protein (N). We measured binding antibody units per mL (BAU/mL) during acute illness within 5 days of illness onset and during convalescence in 105 ambulatory patients with laboratory-confirmed SARS-CoV-2 infection with Omicron variant viruses. Comparing acute- to convalescent phase antibody concentrations, geometric mean anti-N antibody concentrations increased 47-fold from 5.5 to 259 BAU/mL. Anti-RBD antibody concentrations increased 2.5-fold from 1258 to 3189 BAU/mL.

Anti-SARS-CoV-2 Antibody Levels Associated with COVID-19 Protection in Outpatients Tested for SARS-CoV-2, US Flu VE Network, October 2021-June 2022.

Background: We assessed the association between antibody concentration ≤5 days of symptom onset and COVID-19 illness among patients enrolled in a test-negative study. Methods: From October 2021-June 2022, study sites in seven states enrolled and tested respiratory specimens from patients of all ages presenting with acute respiratory illness for SARS-CoV-2 infection using rRT-PCR. In blood specimens, we measured concentration of anti-SARS-CoV-2 antibodies against the ancestral strain spike protein receptor binding domain (RBD) and nucleocapsid (N) antigens in standardized binding antibody units (BAU/mL). Percent reduction in odds of symptomatic COVID-19 by anti-RBD antibody was estimated using logistic regression modeled as (1-adjusted odds ratio of COVID-19)×100, adjusting for COVID-19 vaccination status, age, site, and high-risk exposure. Results: A total of 662 (33%) of 2,018 symptomatic patients tested positive for acute SARS-CoV-2 infection. During the Omicron-predominant period, geometric mean anti-RBD binding antibody concentrations measured 823 BAU/mL (95%CI:690-981) among COVID-19 case-patients versus 1,189 BAU/mL (95%CI:1,050-1,347) among SARS-CoV-2 test-negative patients. In the adjusted logistic regression, increasing levels of anti-RBD antibodies were associated with reduced odds of COVID-19 for both Delta and Omicron infections. Conclusion: Higher anti-RBD antibodies in patients were associated with protection against symptomatic COVID-19 during emergence of SARS-CoV-2 Delta and Omicron variants.