Nessma Adil Mahmoud Yousif

• Background: Several COVID-19 vaccines were authorized by the end of 2020, resulting in the launching of vaccination campaigns, and from a global point of view, the return to normalcy appeared feasible. However, concerns about the safety of COVID-19 vaccines surfaced, due to their rapid emergency approval. In reality, the problem of antibody-dependent enhancement posed a challenge in the context of COVID-19 vaccines’ development. Methods and findings: We introduce a complex extension of the model underlying the pandemic preparedness tool CovidSim 1.1 (http://covidsim.eu/) and an altered version of the model published by Adil et al. in [1] to evaluate the effect of vaccination on the spread of the disease, accounting for ADE, and parameters such as vaccination campaigns onset, vaccination coverage, schedules, rates, and vaccine efficacy. Vaccines are not expected to immunize perfectly. Some individuals fail to immunize, only some might gain partial immunity, and – importantly – some develop antibodydependent enhancement, which raises the possibility of developing symptomatic and severe episodes upon infection. Only a subset of the population will be vaccinated due to vaccination hesitancy or contraindications. The model is intended to facilitate policy-making when aiming to control and stop the spread of SARS-CoV-2. The model can also be used to fit empirical data and infer the real value of some of the model parameters. To exemplify the usage of the model, it is parameterized to reflect the situation in Germany. Based on the control strategies put in place in Germany until late 2020, the model predicted increased incidence (and prevalence) in early 2021 followed by a decrease during the summer period. Assuming a lift in contact reductions (curfews, social distancing, etc.) in summer, disease incidence peaked again. Fast vaccine deployment contributes to reducing disease incidence in the first quarter of 2021 and postponing the epidemic outbreak after the summer season. Coverage of 75% - 80% is necessary to prevent an epidemic peak without further drastic contact reductions. Furthermore, ADE was assumed to increase the mortality rate to 20% from 7%, however, its impact on mortality is minimal with highly effective vaccines but significant with low effectiveness. High vaccination coverage (e.g., 60%) reduces ADE incidence and mortality and a vaccination coverage of 80% reduces the death among vaccinated considerably, while lower coverage increases them. These findings highlight the importance of effective vaccines and high coverage in mitigating ADE’s adverse effects on public health. Conclusions: With availability of the vaccine, adherence with contact reductions is likely to decline. In order to prevent more economic damage from COVID-19, before the flu season in 2022, we need to reach high levels of immunization, while vaccination strategies and disease management need to be adjusted with flexibility. The predictive model can serve as a refined decision-support tool for COVID-19 management.