evidence: The World Health Organization (WHO) has warned against describing the Omicron variant as mild, saying it is killing people across the world. [...] But the record number of people catching it has left health systems under severe pressure, said WHO chief Dr Tedros Adhanom Ghebreyesus. [...] The WHO - the UN's health agency - said the number of global cases has increased by 71% in the last week, and in the Americas by 100%. It said that among severe cases worldwide, 90% were unvaccinated.