Related Experiment Video
Updated: May 21, 2026

A Method of Trigonometric Modelling of Seasonal Variation Demonstrated with Multiple Sclerosis Relapse Data
Published on: December 9, 2015
Assessing the effect of vaccine on spontaneous abortion using time-dependent covariates Cox models
Ronghui Xu1, Yunjun Luo, Christina Chambers
1Department of Family and Preventive Medicine, University of California, San Diego, La Jolla, CA, USA. rxu@ucsd.edu
Purpose:
In studying the safety of vaccine for influenza A (H1N1) given during pregnancy, spontaneous abortion (SAB) is one of the important points to consider. Because women may receive the vaccine any time during their pregnancy, evaluation of the effect of the vaccine on SAB should only take place after vaccination and in the risk window for SAB, that is, the first 20 weeks of gestation. In addition, when such studies are conducted through pregnancy registries where recruitment occurs after pregnancy recognition, the accrued subjects are left truncated in the sense that they are not followed from the start of pregnancy.
Methods:
As previously reported, left truncation needs to be properly handled using survival analysis methods to avoid bias. In the context of time-dependent vaccine exposure, a time-dependent covariate Cox model can be used to simultaneously take into account the left truncation and the vaccine exposure timing.
Results:
In this communication, we illustrate the approach using the Vaccine and Medication in Pregnancy Surveillance System data. We explain in details how the model is fitted using different software.
Conclusions:
We recommend survival analysis methods together with collection of necessary data to study the effects of vaccine on SAB.
Related Concept Videos
Pharmacodynamic Models: Additive and Proportional Drug Effect Model
Comparing the Survival Analysis of Two or More Groups
Statistical Methods for Analyzing Epidemiological Data
Assumptions of Survival Analysis
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
Parametric Survival Analysis: Weibull and Exponential Methods
Weibull Distribution
The Weibull distribution is a flexible model used in parametric survival analysis. It can handle both increasing and decreasing hazard rates, depending on its shape parameter...