Disentangling the effect of measures, variants and vaccines on SARS-CoV-2 Infections in England: A dynamic intensity model

In this paper, we estimate the path of daily SARS-CoV-2 infections in England from the beginning of the pandemic until the end of 2021. We employ a dynamic intensity model, where the mean intensity conditional on the past depends both on past intensity of infections and past realised infections. The model parameters are time-varying and we employ a multiplicative specification along with logistic transition functions to disentangle the time-varying effects of non-pharmaceutical policy interventions, of different variants and of protection (waning) of vaccines/boosters. We show that earlier interventions and vaccinations are key to containing an infection wave. We consider several scenarios that account for more infectious variants and different protection levels of vaccines/boosters. These scenarios show that, as vaccine protection wanes, containing a new wave in infections and an associated increase in hospitalisations in the near future will require further booster campaigns and/or non-pharmaceutical interventions.