What we know about the XBB.1.5 COVID variant sweeping the Northeast

The minor XBB.1.5 omicron variant is raising concerns about a potential increase in COVID-19 cases as it sweeps through the Northeast.

Officials have warned in recent weeks that the strain is highly contagious, can more easily evade immunity offered by vaccines or previous infections than earlier variants – and is likely to increase cases across the country.

The subvariant has already spread rapidly in the Northeast, where it is estimated to cause about 72 percent of infections.

Data from the Centers for Disease Control and Prevention showed last week that XBB.1.5 was the most prevalent subvariant in the US overall, accounting for 40.5 percent of cases in the country. But that information is subject to change as more data is collected from states, and XBB.1.5's share of U.S. cases has fallen to about 27.6 percent as of Friday.

But while another subvariant of Omicron, BQ.1.1, still dominates the country beyond the Northeast, XBB.1.5 has also reached all other regions of the US, and officials predict it will continue to spread. Because of its recent emergence, data on XBB.1.5 is limited, but health officials have revealed some key information about the strain, as well as what questions remain unanswered.

Here's what you know about XBB.1.5:

The “most contagious” omicron subvariant so far

XBB.1.5 is “the most infectious subvariant yet detected” of the already highly contagious omicron strain, Maria Van Kerkhove, technical lead of the World Health Organization's (WHO) response to COVID-19, said in a recent briefing.

Van Kerkhove attributed the subvariant's high transmissibility to the mutations it carries, allowing it to “stick to the cell and reproduce easily.”

Ashish Jha, the White House's COVID-19 response coordinator, agreed with Van Kerkhove's assessment, saying on Twitter that XBB.1.5 was likely more capable of evading immunity than previous omicron subvariants.

People who are not newly infected with or vaccinated against COVID-19 likely have “very little protection against infection” caused by XBB.1.5, Jha further advises.

Cases are expected to increase

The northeastern regions of the country have already seen a recent increase in cases, according to data from the Department of Health and Human Services. Hospitalizations in these areas have also increased between 10 and 15 percent, although it remains to be seen whether XBB.1.5 causes more severe disease than previous subvariants and is behind this jump.

Food and Drug Administration Commissioner Robert Califf said speaking about XBB.1.5 this week that he expects a further increase in cases.

“Variant XBB and its related variants (XBB.1 & XBB.1.5) are crossing the Northeast and will likely move quickly to other areas,” he said. he tweeted.

However, Califf noted that outbreaks caused by XBB.1.5 and other new variants do not appear to be more severe than those caused by older strains of the virus.

“At this point, we are experiencing an increase in cases without evidence of increased disease severity associated with these variants,” he said.

Van Kerkhove echoed Califf's prediction, saying: “We expect further waves of infection around the world.”

“But,” he added, “this need not translate into further waves of death because our countermeasures continue to work.”

It was first detected in the US before spreading worldwide

While XBB, the subvariant from which XBB.1.5 is derived, was first identified in India, the latest mutation is believed to have been first identified in the US in October.

It has since been detected in 29 other countries, according to the WHO. About a dozen countries in the European Union alone have detected XBB.1.5, although levels of the subvariant remain low there, according to the European Center for Disease Prevention and Control.

It is a recombinant virus. What does this mean?

XBB.1.5 is considered a recombinant virus, meaning it carries genetic data from two previous viral mutations.

The subvariant is derived from XBB, which in turn has genetic data from two viral strains derived from the BA.2 'stealth' subvariant. This strain, characterized by mutations that made it difficult to track with PCR tests, was the most prevalent in the US in early 2022 before being overtaken by two other omicron subvariants, BA.4 and BA.5.

Treatments and vaccines are likely to still be effective

Currently, the countermeasures are still expected to be effective in treating COVID-19 infections caused by XBB.1.5 and in reducing the severity of the disease, Van Kerkhove said.

Tza said the updated bivalent COVID-19 booster is still the “best protection” against infection and serious illness.

Califf noted that while this enhancer has been observed to be less effective at neutralizing the XBB strain compared to the ancestral strain, the neutralization it provided was still strong enough to provide “some degree of protection.”

Columbia University researchers found in an early preprint study that subvariants derived from the BQ and XBB lines are better than previous strains at avoiding neutralizing antibodies. Neutralizing antibodies, which can be obtained through previous infections or vaccinations, stop infections by binding to viruses and preventing them from attaching to cells.

Mutations and changes in the SARS-CoV-2 virus can make it harder for neutralizing antibodies to recognize and detect the virus when it enters a person's system, allowing the virus to evade an immune response that might otherwise prevent it from causing infection .

However, the researchers noted that vaccines have yet to prove effective against such strains.

“It is important to emphasize that although infections may now be more likely, COVID-19 vaccines have been shown to remain effective in preventing hospitalization and severe disease even against Omicron, as well as possibly reducing the risk of post- of acute sequelae of COVID-19 (PASC or long COVID),” they said.

Oral antivirals such as Paxlovid and molnupiravir are also expected to be effective against XBB.1.5, as they work not by boosting antibodies – which the strain seems best at avoiding – but by interfering with the virus's ability to replicate.