Neutralizing antibodies are a good indicator of protection,
- not only against severe disease
- but also (if amounts are very high) against viral replication in the mucosa (with or without symptoms), thereby reducing transmission. #COVID19
1/ Omicron's 3 mutations (P681H, H655Y, N679K) in furin cleavage site region were initially predicted to favor its pathogenicity: cell-cell fusion & syncytia formation.
But reality is different.
Omicron's cleavage efficiency is substantially lower than Delta variant. #COVID19
2/ Omicron spike is relatively poorly cleaved.
It shows impaired entry & replication in lung cells that express TMPRSS2, a serine protease enriched in lung alveolar type 1 & 2 cells.
This reduced cleavage is also associated with poorer cell-cell fusion and syncytia formation.
3/ Cell-cell fusion mediated by spike glycoprotein requires S1/S2 cleavage, but is also dependent on TMPRSS2 presence.
Fusogenicity of Omicron spike was severely impaired despite TMPRSS2 expression, leading to marked reduction in syncytium formation compared to Delta spike.