Effects of strict public health measures on seroprevalence of anti-SARS-CoV-2 antibodies during pregnancy.

INTRODUCTION: A substantial number of people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remain asymptomatic throughout the course of infection. Nearly half of pregnant women with coronavirus disease 2019 (COVID-19) are asymptomatic upon diagnosis; these cases are not without risk of maternal morbidity. Here, we investigated the seroprevalence of anti-SARS-CoV-2 antibodies in an unselected sample of pregnant women in Hong Kong. METHODS: This prospective cohort study included pregnant women who presented for routine Down syndrome screening (DSS) between November 2019 and October 2020; all women subsequently delivered at the booking hospitals. Serum antibodies against SARS-CoV-2 were analysed using a qualitative serological assay in paired serum samples taken at DSS and delivery for all participants. RESULTS: In total, 1830 women were recruited. Six women (0.33%) were seropositive at the DSS visit; this seropositivity persisted until delivery. Of the six women, none reported relevant symptoms during pregnancy; one reported a travel history before DSS and one reported relevant contact history. The interval between sample collections was 177 days (range, 161-195). Among women with epidemiological risk factors, 1.79% with travel history, 50% with relevant contact history, and 0.77% with community SARS-CoV-2 testing history, were seropositive. CONCLUSION: The low seroprevalence in this study suggests that strict public health measures are effective for preventing SARS-CoV-2 transmission. However, these measures cannot be maintained indefinitely. Until a highly effective therapeutic drug targeting SARS-CoV-2 becomes available, vaccination remains the best method to control the COVID-19 pandemic.