Effect of vaccination certification with mass vaccination and non-pharmaceutical interventions on mitigating COVID-19

As COVID-19 vaccines became abundantly available around the world since the second half of 2021, many countries carried out a vaccination certificate (green pass) policy to encourage vaccination and help reopen their economies. This policy granted certified people more freedom of gathering and movement than unvaccinated individuals. Accordingly, pre-existing non-pharmaceutical interventions (NPIs) were adjusted under the vaccination certificate policy. The vaccination certificate also induced heterogeneous behaviors between unvaccinated and vaccinated groups, which complicates the modeling of COVID-19 transmission. Still, limited work is available in evaluating the impact of the green pass policy on COVID-19 transmission using quantitative methods. To characterize the major changes caused by the green pass policy, a modified susceptible-exposed-infected-removed (SEIR) epidemiological model SEIQRD2 is proposed in this paper. By integrating different behavior patterns of unvaccinated and vaccinated groups under the green pass policy, SEIQRD2 adopts the inherent variability and complexity of human behaviors in the context of vaccination and NPIs and their effect on COVID-19 transmissions. Three countries: Greece, Austria, and Israel are selected as case studies to demonstrate the validity of SEIQRD2. The simulation results illustrate that the combination of NPIs and vaccination still plays a pivotal role in containing the resurgence of COVID-19 by enforcing vaccination certification.