Editors note: This story has been updated to reflect the Centers for Disease Control and Prevention’s revised numbers released on Friday, Jan. 6.

World Health Organization officials have expressed concern about a new omicron subvariant of the coronavirus — its most transmissible yet. The variant is rapidly increasing around the nation, including Georgia and contributing to a winter wave of COVID-19 cases.

The XBB.1.5 subvariant, which has been circulating since at least October and is known to have spread to 29 countries, is the most transmissible version of the omicron variant detected by health officials so far, WHO officials reported on Wednesday.

The variant appears to be better at evading immune defenses gained from vaccination and prior infection, but at this point, XBB.1.5 doesn’t appear to cause more serious illness than its predecessors, based on laboratory studies on the variant reported in the scientific journal Cell.

A look at how much this subvariant has steadily grown over recent weeks in Georgia and several other states in the southern region, including Alabama, Florida, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee.

17.3% — New COVID cases that are XBB.1.5 for the week ending Jan. 7

10.3% — New COVID cases that were XBB.1.5 for the week ending Dec. 31.

5.8% — New COVID cases that were XBB.1.5 for the week ending Dec. 24.

27.6% New COVID-19 cases around the U.S. that are XBB.1.5 for the week ending Jan. 7

SOURCE: Variant surveillance reports from the Centers for Disease Control and Prevention. The variant percentage estimates are based on the genetic sequencing of PCR tests conducted in a laboratory and do not include home test results.

The Associated Press contributed to this report.