Fig 1.
Flow chart of the overall study design and sampling workflow.
The diagram summarizes participant recruitment and blood sampling at two time-points. At Time-point 1, 987 individuals from urban and rural households were enrolled in a cross-sectional and longitudinal study, and serum samples were collected for ELISA and surrogate virus neutralization testing. After one year, 212 participants returned for Time-point 2 follow-up sampling, and the same serologic assays were performed to assess SARS-CoV-2 antibody responses over time.
Table 1.
Distribution of Sociodemographic Characteristics Among Study Participants.
Fig 2.
Distribution of COVID-19 vaccination status among study participants.
Bar chart showing the distribution of vaccinated and unvaccinated individuals and the relative proportions of specific vaccine products. Vaccinated, type unknown represents participants who reported vaccination, but their vaccine cards were missing and could not confirm the specific brand. Values shown are counts with corresponding percentages.
Fig 3.
SARS-CoV-2 seroprevalence over time in urban and rural communities.
This figure presents a line plot illustrating the proportion of participants with dual anti-spike (S) and anti-nucleocapsid (N) IgG seropositivity at baseline (TP1) and follow-up (TP2) in urban and rural areas. Points represent group-level point prevalence estimates (%), with lines connecting the timepoints, but 95% confidence intervals (CIs), calculated using the normal approximation method are provided for clarity.
Table 2.
Sociodemographic Characteristics and SARS-CoV-2 S and N Protein Antibody Status.
Table 3.
Changes in Combined S and N Antibody Seroprevalence over Time in Urban and Rural Populations.
Fig 4.
Baseline and longitudinal inhibition profiles of selected participants.
Panel A, shows the distribution of percentage inhibition values at baseline, illustrating the variability in neutralising antibody activity across participants. Panel B presents paired baseline and one-year follow-up inhibition values, with connecting lines depicting individual-level changes and highlighting the overall decline in neutralising activity over time. The dashed horizontal line indicates the 30% inhibition threshold for neutralising antibody positivity.
Fig 5.
Immune response markers by vaccination status.
Bars show the proportion positive (%) for spike (S), nucleocapsid (N), dual S&N, and neutralization at baseline and follow-up, stratified by vaccination; error bars denote 95% CIs. At baseline, neutralization was higher in vaccinated (99.3%) than unvaccinated (95.7%). At follow-up, S remained 100% in both groups, while N was 59.0% (95% CI 50.1–67.9) vs 56.5% (44.8–68.2), and S&N was 54.3% (45.7–63.0) vs 56.5% (44.8–68.2) in vaccinated vs unvaccinated, respectively, consistent with persistence partly attributable to vaccine-induced immunity.