Phase 3 clinical trials and real-world effectiveness studies showed that China’s two main inactivated COVID-19 vaccines are very effective against serious illness. In November 2021, an outbreak occurred in the Inner Mongolia Autonomous Region that provided an opportunity to assess the vaccine effectiveness (VE) of these inactivated vaccines against COVID-19 caused by the delta variant. We evaluated VE with a retrospective cohort study of close contacts of infected individuals, using a generalized linear model with binomial distribution and log-link function to estimate risk ratios (RR) and VE. A total of 8842 close contacts were studied. Compared with no vaccination and adjusted for age, presence of comorbidity, and time since last vaccination, full vaccination reduced symptomatic infection by 62%, pneumonia by 64% and severe COVID-19 by 90%; reductions associated with homologous booster doses were 83% for symptomatic infection, 92% for pneumonia and 100% for severe COVID-19. There was no significant decline in two-dose VE for any outcome for up to 325 days following the last dose. There were no differences by vaccine brand. Inactivated vaccines were effective against delta-variant illness, and were highly effective against pneumonia and severe COVID-19; VE was increased by booster doses.

Hepatitis B virus (HBV) infection remains a major public health concern among pregnant women, with regional disparities in epidemic characteristics that hinder precise prevention of mother-to-child transmission (MTCT). This study aimed to characterize the seroepidemiological profiles of HBV infection and identify its associated influencing factors among pregnant women in Nanning City, providing evidence-based insights for optimizing targeted interventions to block HBV MTCT. A stratified cluster random sampling strategy was adopted to recruit pregnant women receiving routine antenatal care at designated medical institutions across Nanning between October 2024 and May 2025. Standardized face-to-face questionnaires were administered to collect demographic, behavioral, and disease-related data. Venous blood samples were collected for quantitative detection of five serological HBV markers via chemiluminescence immunoassay. The Kruskal–Wallis test was used to compare the geometric mean concentration (GMC) of hepatitis B surface antibody (HBsAb), while the chi-square test was applied to analyze intergroup differences in the seropositivity rates of the five HBV markers. Multivariate unconditional logistic regression models were constructed to explore factors independently associated with seropositivity of hepatitis B surface antigen (HBsAg), HBsAb, and hepatitis B core antibody (HBcAb). A total of 1,935 eligible pregnant women were enrolled. The overall seropositivity rates of HBsAg, HBsAb, hepatitis B e-antigen (HBeAg), hepatitis e-antibody (HBeAb), and HBcAb were 6.98%, 59.48%, 1.50%, 15.50%, and 33.02%, respectively. Seropositivity of HBsAg, HBsAb, HBeAb, and HBcAb exhibited an age-dependent ascending trend, with the lowest rates observed in the 14–19 age group and peak rates in the 40–49 age group. Rural residents presented significantly higher HBsAg and HBeAb seropositivity but lower HBsAb seropositivity compared with urban counterparts. Participants with unknown or no prior HBV vaccination history showed markedly higher seropositivity of HBsAg, HBeAg, HBeAb, and HBcAb, alongside reduced HBsAb positivity, relative to those vaccinated within the past 5 years or ≥5 years prior (all P < 0.001). Furthermore, individuals vaccinated ≥5 years ago demonstrated higher HBV marker seropositivity and lower HBsAb positivity than those vaccinated within 5 years (all P < 0.001). Multivariate logistic regression revealed that advanced maternal age, rural residency, comorbid chronic underlying diseases, and close contact with HBV carriers/patients were independent risk factors for HBsAg seropositivity, whereas prior HBV vaccination exerted a protective effect. Advanced age, higher educational attainment, and HBV vaccination history independently predicted higher odds of HBsAb positivity; rural residency, chronic comorbidities, and non-medical occupational status were risk factors for insufficient HBsAb seroconversion. For HBcAb seropositivity, advanced age, chronic underlying diseases, and exposure to HBV-infected individuals were independent risk factors, while higher education and vaccination history served as protective factors. HBV prevalence among pregnant women in Nanning exceeds the national average, accompanied by prominent urban–rural disparities. Advanced maternal age and the presence of chronic comorbidities increase HBV infection vulnerability, while vaccination coverage among childbearing-age women remains suboptimal with progressive attenuation of protective antibody titers over time. We recommend targeted booster HBV vaccination for childbearing-age women with insufficient HBsAb levels to curb incident HBV infections and mitigate the risk of vertical transmission.

Objectives: This cross-sectional study characterized HBV serological profiles and associated factors among pregnant women in Nanning to inform targeted MTCT prevention strategies. Methods: A total of 1935 pregnant women were enrolled via stratified cluster random sampling from October 2024 to May 2025. Five HBV serological markers were quantified by chemiluminescence immunoassay. Multivariable analysis identified factors associated with HBsAg, HBsAb, and HBcAb positivity. HBsAb geometric mean concentration (GMC) and ratio (GMR) were calculated. Results: The overall seropositivity rates (with 95% CI) of HBsAg, HBsAb, HBeAg, HBeAb, and HBcAb were 6.98% (5.92–8.20%), 59.48% (57.28–61.65%), 1.50% (1.05–2.14%), 15.50% (13.96–17.18%), and 33.02% (30.96–35.15%), respectively. HBsAg, HBeAb, and HBcAb positivity increased with age. The HBsAb GMC among uninfected pregnant women was 4.63 mIU/mL (95% CI: 3.72–5.75). Rural pregnant women had lower HBsAb seropositivity than urban counterparts. Unvaccinated women or those with unknown vaccination status showed higher HBsAg, HBeAg, HBeAb, and HBcAb positivity, and lower HBsAb seropositivity, compared with vaccinated women. Advanced age, chronic comorbidities, and HBV exposure were risk factors for HBsAg positivity, whereas HBV vaccination was protective. For HBsAb, higher education and vaccination were protective; advanced age, rural residence, chronic comorbidities, and non-medical occupations were risk factors. For HBcAb, advanced age, chronic comorbidities, and HBV exposure were risk factors, while higher education and vaccination were protective. Conclusions: Pregnant women in Nanning have a high HBV prevalence and insufficient immune protection. Targeted prevention strategies for reproductive-age women are urgently needed to reduce vertical transmission risk.