Dynamic Changes and Trends of SARS-CoV-2 Antibodies Induced by Infection and Vaccination Across Multiple Time Points

Abstract

As the COVID-19 pandemic continues, increasingly complex vaccination and infection histories have made it urgent to investigate the antibody dynamics in populations with hybrid immunity. This study aimed to explore the multi-time-point dynamics of SARS-CoV-2 IgG antibody levels in a community-based population in Jiangsu Province, China, following the Omicron BA.5 wave, as well as the long-term persistence of IgG antibodies nearly 2 years postinfection. A total of 2737 participants across Jiangsu Province were followed up at three different time points over a 6-month period (December 2022-June 2023). Additionally, a cross-sectional serological survey was conducted in October 2024, involving 230 participants to assess long-term antibody persistence. We used generalized additive models to fit antibody dynamics curves, generalized linear mixed models to explore factors influencing antibody levels, and Kaplan-Meier survival analysis to estimate cumulative seroreversion rates. Our findings revealed that, following the large-scale Omicron BA.5 infections, over 85% of the population initially exhibited seropositive IgG levels. Older individuals (> 65 years) had significantly lower antibody levels and faster rates of decline compared to younger participants. Booster immunization reduced the risk of seroreversion by 59.79% (95% CI: 29.63%-76.46%), while individuals with multiple infections experienced slower antibody decay. In the cross-sectional survey conducted 22 months postinfection, the IgG seropositivity rate remained high, exceeding 98%, indicating sustained immunity at the population level. This study provides valuable insights into the dynamics and persistence of IgG antibody levels following large-scale infection. The results underscore the importance of tailored booster immunization strategies to sustain long-term immunity, especially in vulnerable groups like the elderly. Additionally, ongoing serological monitoring is essential for assessing population immunity and informing future vaccination strategies.

Keywords: SARS‐CoV‐2 IgG dynamics; booster immunization; hybrid immunity; seroepidemiology.

Figure 1

Flowchart of participant enrollment and follow‐up in the antibody survey.

Figure 2

Predicted Log‐transformed IgG Antibody Levels and Dynamics Across Different Groups. (A) The predicted log‐transformed IgG antibody levels (S/CO) over the follow‐up period, showing peaks and valleys across three rounds of follow‐up. (B) Age‐stratified predicted IgG antibody levels with separate curves for participants aged < 18, 18–65, and > 65 years. (C) Vaccination status‐stratified predicted IgG antibody levels, comparing unvaccinated/partially immunized participants, fully immunized participants, and those who received a booster dose. (D) Infection history‐stratified predicted IgG antibody levels, comparing participants with no prior infection, one infection, and two or more infections. The dashed vertical lines represent the timing of the follow‐up visits, and the shaded regions indicate 95% confidence intervals.

Figure 3

Cumulative incidence of seroreversion across different groups. (A) Cumulative incidence of seroreversion by age group (< 18 years, 18–65 years, and > 65 years). (B) Cumulative incidence of seroreversion by vaccination status (unvaccinated/partially immunized, fully immunized, and received booster dose). (C) Cumulative incidence of seroreversion by infection history (no infection, one infection, two or more infections). (D) Cumulative incidence of seroreversion in participants aged > 65 years, comparing those who received a booster dose with those who did not. The shaded regions around the lines represent the 95% confidence intervals, and the p‐values reflect the statistical significance of the differences between the groups. The tables below each plot display the cumulative number of seroreversion events at different time points for each group.

Figure 4

Long‐term IgG Antibody Levels and Seropositivity Rates Following Omicron BA.5 Infection. The log‐transformed IgG antibody levels (S/CO) across four time points following the Omicron BA.5 wave, measured at 2, 4, 6, and 22 months postinfection. Each violin plot represents the distribution of IgG levels at the respective time point, with the median indicated by the dashed line. The seropositivity rate is shown above each plot. Statistical significance between time points is indicated by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).