New omicron variants are bypassing natural immunity from prior COVID-19 infections and could be enough to spark a new wave, according to a study out of South Africa.

Scientists examining omicron’s BA.4 and BA.5 sublineages saw increased infection rates in people who had omicron but weren’t vaccinated, compared to their vaccinated counterparts. Scientists took blood samples from 39 people, 15 of whom were vaccinated.