According to preliminary
data from Kei Sato at the University of Tokyo and colleagues, BA.4, BA.5 and BA.2.12.1 may have evolved to refavour infection of lung cells, rather than upper respiratory tract tissue – making them more similar to earlier variants, such as Alpha or Delta. The propensity of earlier Omicron variants to prefer infecting non-lung tissue may be one reason why infections tend to be milder in most people.
“It looks as though these things are switching back to the more dangerous form of infection, so going lower down in the lung,” Dr Stephen Griffin, a virologist at the University of Leeds, said.
Sato’s experiments indicate that BA.4, BA.5 and BA.2.12.1 replicate more efficiently in human lung cells than BA.2, while further experiments in hamsters suggest that BA.4 and BA.5 may cause more severe disease.