Omicron XBB.1.5 Does Not Carry Mutations Known to Increase Severity of Virus: WHO

A sign of the World Health Organization in Geneva, Switzerland, on April 24, 2020. Fabrice Coffrini/AFP via Getty Images

The Omicron XBB.1.5 variant of COVID-19 does not have any mutations known to increase the severity of the virus in individuals, according to the World Health Organization (WHO).

In a risk assessment (pdf) published on Jan. 11, the health agency said that the XBB.1.5 variant “does not carry any mutation known to be associated with potential change in severity.”

“Based on its genetic characteristics and early growth rate estimates, XBB.1.5 may contribute to increases in case incidence globally,” the agency said.

However, it noted that “to date, the overall confidence in the assessment is low as growth advantage estimates are only from one country, the United States of America.”

The risk assessment comes as the Biden administration on Jan. 11 extended the COVID-19 state of emergency following consultation with public health officials.

“The COVID-19 Public Health Emergency remains in effect, and as HHS [the Department of Health and Human Services] committed to earlier, we will provide a 60-day notice to states before any possible termination or expiration,” a spokesperson for HHS told media outlets.

Wednesday’s extension means the public health emergency has been renewed every 90 days since it was first issued under the Trump administration in January 2020, when the pandemic began.

The renewal comes as the XBB.1.5 variant is fast becoming the dominant subvariant in the United States. Data from the Centers for Disease Control and Prevention (CDC) show that XBB.1.5 accounted for an estimated 27.6 percent of COVID-19 cases in the country for the week ending Jan. 7.

The BQ.1.1 variant, which was first identified in September, still accounts for the largest number of cases at 34.4 percent, according to the data.

XBB.1.5 Most Resistant to Antibodies

According to the WHO’s risk assessment, XBB.1.5 is one of the COVID-19 subvariants that is most resistant to antibodies acquired from vaccination or previous infection.

“These data reported that sera (serum) from individuals with a) BA.1, b) BA.5 or c) BF.7 breakthrough infection and three doses of the inactivated vaccine (Coronavac) or d) BA.5 infection following three or four doses of mRNA vaccine (BNT162b2 or mRNA-1273) do not induce high neutralization titers against XBB.1.5,” the WHO said in its report.

While it is the most resistant to antibodies, symptoms of XBB.1.5 are thought to be similar to those of previous strains of Omicron, such as fever, headaches, and other flu-like symptoms.

Most people develop symptoms around five days after exposure to the strain, according to Andy Pekosz, a professor of molecular microbiology and immunology and co-director of Johns Hopkins Center of Excellence in Influenza Research and Surveillance.

Barbara Mahon, head of the CDC’s proposed Coronavirus and Other Respiratory Viruses Division, also told CBS News that there is no suggestion that XBB.1.5 is more severe than previous strains of Omicron.

Elsewhere, Maria Van Kerkhove, the WHO’s COVID-19 technical lead, told CNBC on Jan. 4 that while XBB.1.5 is the most transmissible version of COVID-19 yet, it doesn’t appear to increase the severity of the virus in individuals.

“The reason for this are the mutations that are within this subvariant of Omicron allowing this virus to adhere to the cell and replicate easily,” Kerkhove said. “The more this virus circulates the more opportunities it will have to change.”

While the WHO in its risk assessment said further data and laboratory testing are needed from other countries on how fast XBB.1.5 is spreading and how severe it is, researchers are still cautious about what impact the strain may have on the United States and the rest of the world.