Is Boris right to fear the Omicron variant?

Boris Johnson announced a new raft of coronavirus measures on Saturday, after two cases of the Omicron variant were detected in the UK. Face masks will soon be made mandatory in shops and on public transport and  PCR tests compulsory for those travelling to the UK. These new restrictions were revealed less than half a week after health authorities in South Africa informed the World Health Organisation of the discovery of the new Covid-19 variant, designated B.1.1.529 and now re-named Omicron. First isolated on 9 November, on Saturday two cases of the virus were detected in Britain, in Essex and Nottinghamshire. Is Boris Johnson right to fear this new variant?