# Comparative Analysis of Anti-receptor Binding Domain (RBD) IgG Responses to Homologous and Heterologous SARS-CoV-2 Vaccine Regimens: A Study From Bangladesh

## TL;DR

This study from Bangladesh compares immune responses to same and different vaccine boosters for SARS-CoV-2, finding that same vaccines produce higher antibody levels while different vaccines boost more significantly.

## Contribution

The study provides new insights into the immunogenicity of homologous versus heterologous SARS-CoV-2 vaccine regimens in a real-world setting.

## Key findings

- Homologous vaccine regimens resulted in higher anti-RBD IgG levels compared to heterologous regimens.
- Heterologous regimens showed a greater fold increase in anti-RBD IgG levels, indicating stronger immune recall.
- Diabetes and hypertension significantly reduced antibody responses, especially in the heterologous group.

## Abstract

Background: The COVID-19 pandemic necessitated robust vaccination strategies, including booster doses to sustain immunity against SARS-CoV-2. The comparative immunogenicity of homologous (same vaccine type) versus heterologous (different vaccine types) booster regimens remains understudied, particularly in diverse settings. This study assesses anti-receptor binding domain (RBD) IgG antibody responses to these regimens in Bangladesh.

Materials and methods: A prospective quasi-experimental study was conducted at Bangabandhu Sheikh Mujib Medical University, Dhaka, Bangladesh, from March 2022 to February 2023. Seventy-three participants, selected via convenience sampling, were grouped into homologous (n=40) or heterologous (n=33) vaccine regimens based on primary and booster vaccine types. Anti-RBD IgG levels were measured pre-booster and three weeks post-booster using the SARS-CoV-2 IgG II Quant Reagent Kit (Abbott, Ireland). Demographic and clinical factors (age, sex, BMI, diabetes, and blood pressure) were evaluated. Mann-Whitney U and Kruskal-Wallis tests were used, with p≤0.05 indicating significance.

Results: Participants (mean age: 35.51 years, 79.5% male) showed higher pre-booster (median: 4499.65 vs. 1863.7 AU/mL, p<0.001) and post-booster (median: 13835.15 vs. 10423.3 AU/mL, p=0.014) anti-RBD IgG levels in the homologous group compared to the heterologous group. However, the heterologous group exhibited a greater fold increase (median: 4.6 vs. 3.65, p=0.024) of anti-RBD IgG levels. A higher proportion of participants in the homologous regimen achieved high post-booster IgG levels (>20,000 AU/mL, p=0.016). Diabetes significantly reduced antibody responses in the heterologous group (p=0.006). Hypertensive participants had significantly reduced antibody responses before (p=0.005) and after (p=0.001) the booster in the heterologous group and after (p=0.033) the booster in the homologous group. Age, sex, and BMI had no significant effect on the results.

Conclusions: Homologous regimens yield higher anti-RBD IgG levels, while heterologous regimens produce greater fold increases of anti-RBD IgG levels, indicating robust recall. Diabetes and hypertension impair responses, particularly in heterologous regimens. These findings support the need for tailored vaccination strategies to enhance immune protection.