A sub-variant of the highly transmissible Omicron version of coronavirus known as BA.2 is now dominant worldwide, prompting surges in many countries in Europe and Asia and raising concern over the potential for a new wave in the United States.
A summary of what is known about BA.2
BA.2 now represents nearly 86% of all sequenced cases, according to the World Health Organization. It is even more transmissible than its highly contagious Omicron siblings, BA.1 and BA.1.1, however, the evidence so far suggests that it is no more likely to cause severe disease.
As with the other variants in the Omicron family, vaccines are less effective against BA.2 than against previous variants like Alpha or the original strain of coronavirus, and protection declines over time. However, according to UK Health Security Agency data, protection is restored by a booster jab, particularly for preventing hospitalization and death.
The rise of BA.2 has been blamed for recent surges in China as well as record infections in European countries like Germany and the UK. Yet some European countries are now seeing a slower uptick in new cases or even a decline.
BA.2 has been called the "stealth variant" because it is slightly harder to track. A missing gene in BA.1 allowed it to be tracked by default through a common PCR test. BA.2 and another sibling, BA.3, which is also increasing in prevalence but is currently at low levels, can only be found by genomic sequencing, which some countries do more than others.