Two new sublineages of the Omicron coronavirus variant can dodge antibodies from earlier infection well enough to trigger a new wave but are far less able to thrive in the blood of people vaccinated against Covid-19, South African scientists have found.

The scientists from multiple institutions were examining Omicron's BA.4 and BA.5 sublineages - which the World Health Organization last month added to its monitoring list. They took blood samples from 39 participants previously infected by Omicron when it first showed up at the end of last year.