The role of vaccination roll-out in the monitoring of Covid-19 pandemic spread: a country-level quantitative study

Early detection of contagion surge phases that could potentially mark the beginning of new waves is crucial to monitor the pandemic development and to define proper health policies. The potential availability of reliable covariates can effectively support the monitoring of the pandemic development and provide early warning signals. This paper combines epidemic surge detection with the study of the role of vaccination roll-out, by improving and enhancing the methodology introduced by Agosto and Cerchiello (2024). A covariate-augmented version of the BSADF test for the detection of explosive patterns in time series, named CBSADF test, is used to identify whether the time series of the effective reproduction number moves to explosive behavior, indicating a potential upcoming wave, conditioned on the evolution of the vaccination roll-out. By applying our method to a representative set of European countries, we show that the model can effectively identify upcoming exponential increases in the effective reproduction number and the interplay with the vaccination roll-out.