Speakers - 2025

Biography

Dr. Cao is a Research Scientist at the Immunization Prevention Institute, Beijing CDC, holding an M.D. and Ph.D. in Epidemiology and Medical Statistics from China CDC. His research focuses on vaccine-preventable diseases and population vaccination coverage. Dr. Cao's expertise spans population cohort studies, clinical trial statistical analysis, viral variation and evolution, and real world epidemiology studies. He applies advanced statistical methodologies to immunization program data, generating evidence to strengthen public health strategies. Driven by a commitment to disease prevention, his work translates complex epidemiological findings into actionable insights for optimizing vaccine policy and improving population health outcomes.
 

Abstract

Abstract:

Background: The effect of varicella emergency vaccination (EV) has not been fully evaluated. Meta-analysis on the vaccine effectiveness of varicella EV for controlling outbreaks shows significant heterogeneity, with effectiveness ranging from 0% to 92% for the first dose as EV and from 0% to 89% for the second dose as EV. This poses a challenge for the use and evaluation of EV in the event of a varicella outbreak;

Methods: We conducted an observational cohort study on the impact of EV on the varicella incidence rate in a primary school in Beijing where a disease outbreak occurred. Participants were categorized into five groups based on their immune status: Unvaccinated group, First Dose as EV group, One Dose no-EV group, Second Dose as EV group and Two Doses group. Incidence rate of varicella was calculated by person-time according to different immunization statuses. Multivariate Cox proportional hazards models were applied to assess the effectiveness of the varicella vaccination on disease incidence rate among those students. EV status was treated as time-dependent covariate. For students who received a first-dose as EV or second-dose as EV, disease exposure was quantitatively assessed separately for the time period before and after their transition to vaccinated status. To account for confounding factors, baseline characteristics such as sex, grade, and interval between immunization history and risk exposure were included as control variables in the multivariate analysis. The incremental effectiveness of EV was further examined, limited on the students with classroom exposure for the sensitive analysis;

Results: Demographic characteristics, vaccination details, and disease onset information were 100% (918/918) collected. The crude attack rate was 44% (11/25), 8% (3/36), 11% (24/215), 3% (6/176) and 2% (8/466) among Unvaccinated group, First Dose as EV group, One Dose no-EV group, Second Dose as EV group and Two Doses group, respectively. Compared to the Unvaccinated group and One Dose no-EV group, the first dose varicella vaccine as EV and the second dose as EV offered incremental effectiveness of 90% (95% CI 65%–97%) and 79% (95% CI 47%–92%), respectively;

Conclusions: Both the first dose and the second dose as EV contributed to lower rates of varicella incidence and offered incremental vaccine effectiveness in an outbreak setting. Our study underscores the importance and benefits of initiating emergency varicella vaccination early to reduce the disease incidence rate in an elementary school setting where there was no complete coverage of the two doses of varicella vaccine and an outbreak occurred.