Monitoring Temporal Changes in SARS-CoV-2 Spike Antibody Levels and Variant-Specific Risk for Infection, Dominican Republic, March 2021-August 2022

Abstract

To assess changes in SARS-CoV-2 spike binding antibody prevalence in the Dominican Republic and implications for immunologic protection against variants of concern, we prospectively enrolled 2,300 patients with undifferentiated febrile illnesses in a study during March 2021-August 2022. We tested serum samples for spike antibodies and tested nasopharyngeal samples for acute SARS-CoV-2 infection using a reverse transcription PCR nucleic acid amplification test. Geometric mean spike antibody titers increased from 6.6 (95% CI 5.1-8.7) binding antibody units (BAU)/mL during March-June 2021 to 1,332 (95% CI 1,055-1,682) BAU/mL during May-August 2022. Multivariable binomial odds ratios for acute infection were 0.55 (95% CI 0.40-0.74), 0.38 (95% CI 0.27-0.55), and 0.27 (95% CI 0.18-0.40) for the second, third, and fourth versus the first anti-spike quartile; findings were similar by viral strain. Combining serologic and virologic screening might enable monitoring of discrete population immunologic markers and their implications for emergent variant transmission.

Keywords: COVID-19; Dominican Republic; SARS-CoV-2; coronavirus disease; respiratory infections; severe acute respiratory syndrome coronavirus 2; spike antibody; vaccine-preventable diseases; viruses; zoonoses.

Figure 1

Number of participants (N = 2,300) enrolled per month, by age group, in a study of SARS-CoV-2 spike antibody levels, Dominican Republic, March 2021–August 2022. A) All ages; B) 2–17 years of age; C) >18 years of age. Gray bar sections indicates SARS-CoV-2 NAAT–negative participants; black bar sections indicate SARS-CoV-2 NAAT–positive participants. Labels on x-axis indicate complete months, except March 2021, which represents enrollment starting March 22, 2021, and August 2022, which represents enrollment through August 17, 2022.

Figure 2

SARS-CoV-2 S antibody seroprevalence, titers, and vaccine doses of participants enrolled (N = 2,300) in a study of SARS-CoV-2 S antibody levels, by age group, Dominican Republic, March 2021–May 2022. A–C) Seroprevalence among study participants of all ages (A), 2–17 years of age (B), and >18 years of age (C). Gray dots indicate weekly mean values; increased dot intensity reflected more observations. Blue line indicates locally estimated scatterplot smoothing (LOESS) smoothed seroprevalence; gray shading indicates 95% CI around the smoothed estimate. D–F) Titers among study participants of all ages (D), 2–17 years of age (E), and >18 years of age (F), by week, plotted on a log scale. Each gray dot indicates a unique study participant (n = 1,910). Blue lines indicate LOESS smoothed antibody levels; gray shading indicates 95% CI around the smoothed estimate. Horizontal red line indicates manufacturer recommended cutoff index (>0.800 BAU /mL); values above the line represent a positive result and values below the line a negative result. G–I) Percentage of weekly enrolled participants of all ages (G), 2–17 years of age (H), and >18 years of age (I) who had received >1 (red dots), >2 (green dots), or >3 (blue dots) COVID-19 vaccine doses; increased dot intensity reflects more observations. Colored lines indicate LOESS smoothed percentage; gray shading indicates 95% CI around smoothed percentage. BAU, binding antibody units; S, spike.

Figure 3

Distribution of SARS-CoV-2 S antibody titers among participants in a study of SARS-CoV-2 S antibody levels, Dominican Republic, March 2021–August 2022. A) Smoothed density plot demonstrates log-adjusted distribution of anti-S antibody titers among all study participants (N = 2,300), stratified by date interval when study participants were enrolled from earliest (March–June 2021, upper) to latest (May–August 2022, lower). Study interval labels indicate complete months except March 2021, which represents enrollment starting March 22, 2021, and August 2022, which represents enrollment through August 17, 2022. B) Smoothed density plot demonstrates log-adjusted distribution of S antibody titers among study participants (n = 2,300) stratified by age group. Dark purple shading indicates lower S titers and light green higher titers. C) Smoothed density plot demonstrates log-adjusted distribution of S antibody titers among participants (n = 2,293), stratified by number of COVID-19 vaccine doses received from none (unvaccinated, top plot) to 3 (bottom plot). Darker red shading indicates lower S titers and light orange higher titers. Six participants who received 4 COVID-19 vaccine doses not included. Values for 3 vaccine doses for March–June 2021 period plot not shown given sparsity of datapoints (n = 1). For all plots, gray circles represent titer adjusted individual study participant values. Narrow vertical black lines indicates median values. Lower limit of assay measurement is 0.4 BAU/mL, and values <0.4 BAU/mL are represented as 0.4 BAU/mL, with smoothing extending curves below the lower measurement limit. Therefore, density plot shading is used for illustrative purposes. Table 2 and Appendix Tables 2, 3) summarize data used for plots. BAU, binding antibody units; S, spike.