Objective To explore the importance of post-vaccination serological testing （PVST） for children exposed to hepatitis B virus （HBV）， and analyze the factors affecting the progress of PVST.

Methods The study focused on hepatitis B surface antigen （HBsAg）-positive pregnant women and their newborns residing in Tongzhou District， Beijing， who delivered at various obstetric institutions from January 1， 2020 to March 31， 2022. The obstetric institutions and community health service centers conducted follow-up visits 1 to 2 months after the children had received three doses of the hepatitis B vaccine （HepB）.

Results The vaccination rate of hepatitis B immunoglobulin （HBIg） was 100.00% （800/800）， with a successful PVST follow-up rate of 85.88% （687/800） in Tongzhou District. The initial non-response rate to immunization was 0.29% （2/687）， but successful immunization was achieved after re-immunization. The mother-to-infant transmission rate of hepatitis B was 0. Children who did not undergo PVST accounted for 14.13% （113/800）， with the main reasons being delays due to the COVID-19 pandemic， parents’ reluctance to allow venous blood collection due to the young age of the children， and loss to follow-up because children moved back to their parents’ place of origin. Logistic regression analysis showed that the proportion of PVST was higher among high-risk children （OR=30.009，P=0.001）， children with family residing in Beijing （OR=2.218，P=0.002）， and children whose mothers were <35 years old （OR=1.687，P=0.020）.

Conclusion PVST is necessary for assessing the status of HBV immune response in newborns after vaccination with HepB. The COVID-19 pandemic impacted the implementation of PVST for children exposed to HBV. Strengthening the management of non-high-risk children， those living outside Beijing， and children with mothers aged ≥ 35 years old may increase the rate of PVST in Tongzhou District.