The future for COVID-19 vaccines: public health assessment and perspectives based on scientific evidence

The development and use of messenger RNA-based (mRNA) vaccines against the SARS-CoV-2 spike protein have proven to be highly effective against symptomatic COVID-19, especially for severe forms. Since the declaration of a public health emergency in early 2020, however, the SARS-CoV-2 virus has continuously evolved, giving rise to several variants that have caused and continue to cause concern in the scientific community. Currently, viruses circulating worldwide belong to the Omicron lineage, with several identified sub-variants. In response to virus mutation, mRNA vaccines have been adapted into bivalent vaccines containing two mRNAs: one encoding the original Wuhan SARS-CoV-2 spike protein and one encoding the BA.1 or BA.4-5 spike protein of the Omicron sub-variant. This strategy is based on the hypothesis that the immune system's response improves when variants are included in the vaccine, leading to an increase in the magnitude and diversity of both the humoral and cellular immune response. The evidence gathered to date confirms the use of bivalent vaccines as the optimal strategy. In the light of current knowledge, and in the awareness of the impossibility of making precise predictions on the evolution of the COVID-19 pandemic, as a group of experts we propose some considerations for the progressive evolution of vaccination against SARS-CoV-2 from pandemic to endemic vaccination.