COVID-19 vaccines: evidence, challenges and the future

Through an unprecedented research and development process, in early 2021, just one year after the COVID-19 pandemic started devastating the world, there are several vaccines commercially available or in advances phase of testing, each with its own characteristics and challenges. For the first time in the history of vaccination, a global immunization program has started at a time of intense pandemic activity characterized by high virus transmission, facilitating selection of variants potentially able to escape the vaccine-induced antibody response. The reality is that one cannot rely on a single vaccine when dealing with a pandemic emergency: the urgent need of billions of doses clashes with the production capacity of the pharmaceutical industry. There is therefore no ideal vaccine, but there are many good vaccines to be used immediately. The current international debate about COVID-19 vaccines is today the hottest topic in global health whether it relates to technical and scientific issues or to the ethical aspects of access to vaccinations for all. This article aims at reviewing the status of vaccines that are used, or about to be used, in immunization campaigns worldwide.