The researchers attribute these properties to additional mutations in the spike protein.
Original publication:
Nchioua, R., Diofano, F., Noettger, S. et al. (2022). Strong attenuation of SARS-CoV-2 Omicron BA.1 and increased replication of the BA.5 subvariant in human cardiomyocytes. Sig Transduct Target Ther 7, 395. https://doi.org/10.1038/s41392-022-01256-9
More information:
https://www.aerzteblatt.de/nachrichten/140700/Omicronsubvariante-BA-5-schaedigt-Kardiomyozyten-staerker?rt=8b1a674cf080a3174d3d19d876630244