A retrospective cohort study on the protective effect of influenza vaccination during pregnancy in Gansu Province

To evaluate the Vaccine Effectiveness (VE) of the Influenza Vaccine (InfV) during pregnancy in Gansu province. A retrospective cohort of pregnant women vaccinated with InfV was constructed using the electronic case system and immunization planning system of Gansu province. Outcome information of Influenza-Like Illness (ILI) in pregnant women after vaccination with InfV during the influenza epidemic seasons from 2019 to 2021 was collected. The log-binomial model was used to estimate the adjusted Risk Ratio (<i>RR</i>), VE, and their Confidence Intervals (<i>CI</i>). The incidence rates of the InfV vaccination group and the non-vaccination group during pregnancy in Gansu province were 4.70% (54/1,150) and 6.91% (16,990/245,754), respectively. The adjusted <i>RR</i> was 0.78 (95%<i>CI</i> 0.43-0.75), and the adjusted VE was 22.20 (95%<i>CI</i> 0.79-40.30). Vaccination with InfV during pregnancy in Gansu province from 2019 to 2021 has a protective effect against ILI in pregnant women, and there is no difference in vaccination at different stages of pregnancy.