The latest study showed that omicron's pathogenicity was more lethal for elderly and infants.

The so-called "mildness" of omicron had been debunked by the latest study.  The vulnerable groups (infants and elderly) had depicted the true severity of omicron because they're the least to be affected by exogenous factors (vaccines & covid drugs) that would skew the data.   Although the elderly group is usually the first group to be vaccinated, most of them have pre-existing medical conditions that make them vulnerable.  The infant group is the most suitable segment to determine the pathogenicity of covid because they're unvaccinated.

The chart above showed that BA1 was the most lethal variant for infants and elderly and BA2 and BA5 were more lethal than delta for the same groups.