Studies are underway to find the precise characteristics of the latest Covid-19 variant, BA2. Accounting for over half of sequenced Omicron cases in 57 countries, it appears more transmissible than the original strain and more able to infect the vaccinated. BA2, nicknamed ‘Omicron's little brother’, was mentioned for the first time during a press conference on 20 January and is being scrutinised by scientists. It appears to have a growth advantage compared to the version of Omicron that has swept the globe. Analysis suggests it could be substantial, although there is a risk of over-estimating growth advantage in the early stages. What we know is that it is a growing proportion of cases. There are no precise data yet on its resistance to vaccines or the severity of the cases.