Impact of imprinted immunity induced by mRNA vaccination in an experimental animal model.

The emergence of SARS-CoV-2 Omicron variants has led to concerns that ancestral SARS-CoV-2-based vaccines may not be effective against newly emerging Omicron subvariants. The concept of "imprinted immunity" suggests that individuals vaccinated with ancestral virus-based vaccines may not develop effective immunity against newly emerging Omicron subvariants, such as BQ.1.1 and XBB.1. Here, we investigated this possibility using hamsters. While natural infection induced effective antiviral immunity, breakthrough infections in hamsters with BQ.1.1 and XBB.1 Omicron subvariants after receiving the 3-dose mRNA-LNP vaccine resulted in only faintly induced humoral immunity, supporting the possibility of imprinted immunity.