The latest data released by the US Centers for Disease Control and Prevention has revealed that the Covid cased caused by the Omicron sub-variant XBB.1.5 have doubled in the past week.
Now, more than 40 per cent of the Covid cases in the US are caused by this sub-variant which is "highly immune evasive".
A CNBC report, quoting scientists from Columbia University, said that the rise of XBB subvariants may result in increase in breakthrough infections and re-infections.
Scientists and health experts have been closely monitoring the XBB subvariant family for months. These highly-mutant strains could defeat vaccines, including boosters.
Top US infectious diseases expert Anthony Fauci said in November that updated COVID-19 booster shots - which target the original variant of the coronavirus as well as BA.4 and BA.5 subvariants - would still provide "some protection, but not the optimal protection" against the XBB variant.
Andrew Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, said holiday travel in the US could speed up the XBB subvariant's spread across the country.
"XBB.1.5 is different from its family members as it has an additional mutation that makes it bind better to cells. The virus needs to bind tightly to cells to be more efficient at getting in and that could help the virus be a little bit more efficient at infecting people,” Pekosz was quoted as saying by CNBC.
The American Automobile Association (AAA) had estimated that 112.7 million people planned to travel 50 miles (80 km) or more from home between Dec.30 and Jan. 2, up 3.6 million travelers over last year and closing in on pre-pandemic numbers.
What is XBB.1.5
XBB was first identified in India in August. It quickly become dominant there, as well as in Singapore. It has since evolved into a family of subvariants including XBB.1 and XBB.1.5.
XBB.1.5 not only evades protective antibodies as effectively as the XBB.1 variant, which was highly immune evasive, but also is better at binding to cells through a key receptor.
The earliest BA.5 lineage now represents just a small fraction of cases, having been overtaken by its offshoots, BQ.1 and BQ.1.1, which still remain the dominant variants in the US, though on the decline.
The rise in cases of the new variant comes after the White House Covid response coordinator urged Americans to get their flu vaccines and updated Covid-19 boosters, pointing to rising cases in about 90 per cent of the country ahead of the year-end holidays.
The US will impose mandatory Covid-19 tests on travelers from China, US health officials said on Wednesday (28), joining India, Italy, Japan and Taiwan in taking new measures after Beijing's decision to lift stringent zero-Covid policies.
Beginning on Jan. 5, all air passengers 2 years old and older will require a negative result from a test no more than two days before departure from China, Hong Kong or Macao.
Passengers who test positive more than 10 days before a flight can provide documentation of recovery in lieu of the negative test result, the federal officials said.
The US also is expanding its voluntary genomic sequencing program at airports, adding Seattle and Los Angeles to the program. That brings the total number of airports gathering information from positive tests to seven.
In June, the US rescinded a 17-month-old requirement that people arriving in the country by air test negative for Covid-19. It still requires most non-US citizens to be vaccinated against Covid to travel to the US.
(with agencies)
