The global COVID-19 pandemic continues to claim victims worldwide, representing a health and socioeconomic challenge with few precedents in human history. The therapeutic agents used to treat COVID-19 infection are mostly aimed at avoiding the most serious complications and organ damage that in a percentage of cases can be fatal. Recently, the first COVID-19 vaccines have been authorised, starting a massive vaccination campaign worldwide. The COVID-19 vaccines authorized or under testing use different methods of action such as mRNA, DNA vaccine, viral vector, protein subunit, and virus inactivated immunization strategies. The mRNA vaccines are the first authorised vaccines with this new method of action, initiating a new era of preventive medicine. To date, data indicate that they may be effective against the newly identified SARS-CoV-2 variants. Short-term studies indicated an acceptable safety profile but long-term immunity as well as safety is not yet available. In this article, we briefly describe mRNA vaccines and highlight some aspects yet to be fully defined.