Immune Response to COVID-19 Vaccines: Updates in a Fast-Moving Scenario.

The prompt and extensive use of COVID-19 vaccines has dramatically reduced both cases and casualties, but it has also underscored a number of critical issues that need to be addressed for their full exploitation at global level. This Special Issue was launched to gather fresh data to improve the way we use vaccines that are currently available to contribute to the design and the development of new ones and to elucidate social, ethical and psychological concerns that might hamper vaccine acceptance and use. It includes 15 articles six of which address, under various aspects, the level and durability of protective immunity; five deal with the highly debated field of vaccine use, efficacy and safety, in persons with an impaired/dysregulated immune system; one paper reports on adjuvants' role in immune stimulation; one on the interference of natural adenovirus immunity with DNA vaccine response; one is a review on the cellular mechanisms of vaccine-dependent myocarditis; and one explores social attitudes to vaccines in different ethnic groups during early phases of the pandemic. Far from being complete and exhaustive, this Special Issue provides the reader with fresh insights into several critical questions raised by or connected to the advent of COVID-19 vaccines. This introductory article provides an overview of their contribution, while offering a quick glance at the current state of the art.