Background Clinical characteristics and humoral immune responses in pregnant women following natural SARS-CoV-2 Omicron infection remain unclear, particularly in those previously receiving inactivated vaccines, which may induce immune imprinting and affect cross-neutralization against emerging Omicron subvariants. Methods This cross-sectional investigation was conducted in Zhejiang Province between December 2022 and April 2023. A total of 223 pregnant women with a gestational age of at least six weeks and 31 healthy non-pregnant women were recruited as research subjects and controls. Serum specimens were collected to determine anti-RBD IgG levels by ELISA, alongside pseudovirus neutralizing antibody titers against the prototype strain and Omicron BA.4/5, XBB.1.5 subvariants. Relevant clinical information was gathered through questionnaires, and multivariate regression analysis was applied to identify influencing factors of immune response characteristics. Results Acute COVID-19 symptom profiles were comparable between pregnant women and non-pregnant healthy women (P 0.05). Among questionnaire respondents, pregnant individuals had markedly prolonged symptom recovery, with a notably higher proportion taking over one week to recover (73.0% vs. 23.1%, P = 0.045), and presented a significantly higher medical consultation rate (73.0% vs. 15.4%, P 0.001). For immune response, neutralizing antibody levels against the Omicron BA.4/5 showed no intergroup difference overall. By contrast, pregnant women exhibited significantly lower XBB.1.5 neutralizing antibody titers than controls, with geometric mean titers of 16.35 and 45.96 respectively (P 0.05). Multivariate regression analysis indicated that SARS-CoV-2 infection during the Omicron epidemic was the major independent factor linked to elevated neutralizing antibody levels, while a BMI below 25.0 kg/m² was independently correlated with higher XBB.1.5 neutralizing antibody titers. Additionally, no significant differences in clinical manifestations or immune responses were found among women in different trimesters of pregnancy. Conclusion In vaccine-primed pregnant women with natural Omicron infection, acute clinical manifestations and homologous humoral immunity against BA.4/5 were similar to non-pregnant controls, but symptom recovery was prolonged and cross-neutralization against XBB.1.5 was reduced. No trimester-specific differences were observed.
Bao et al. (Thu,) studied this question.