Predicting the effects of waning vaccine immunity against COVID-19 through high-resolution agent-based modeling

Truszkowska, Agnieszka; Zino, Lorenzo; Butail, Sachit; Caroppo, Emanuele; Jiang, Zhong-Ping; Rizzo, Alessandro; Porfiri, Maurizio

The COVID-19 pandemic is yet again on the verge of escalating, despite a hopeful case decrease recorded during spring and summer 2021, due to successful vaccination roll-outs. Together with the emergence of new variants, the potential waning of the vaccination immunity could pose threats to public health. It is tenable that the timing of such a gradual drop in the immunity of most of the vaccinated population would synchronize with the near-complete restoration of normalcy. Should also testing be relaxed, we might witness a potentially disastrous COVID-19 wave in winter 2021/2022. In response to this risk, many countries, including the U.S., are opting for the administration of an additional vaccine dose, the booster shot. Here, in a projected study with an outlook of six months, we explore the interplay between the rate at which boosters are distributed and the extent to which testing practices are implemented. Projections are based on a highly granular agent-based model that provides a close, one-to-one digital reproduction of a real, medium-sized U.S. town. Focusing on the dominant Delta variant, we contemplate the waning immunity provided by the locally available Johnson&Johnson, Pfizer, and Moderna vaccines. Theoretical projections indicate that the administration of boosters at the rate at which the vaccine is currently administered could yield a severe resurgence of the pandemic, even worse than the first wave experienced in spring and summer 2020. Our projections suggest that the peak levels of mid spring 2021 in the vaccination rate may prevent the occurrence of such a scenario. Our study highlights the importance of testing, especially to detect infection of asymptomatic individuals in the very near future, as the release of the booster reaches full speed.