XBB Subvariant Now Accounts for Half of All COVID Cases in New England

Three omicron subvariants that more easily dodge immunity are now causing 90% of COVID-19 infections in New England, according to the latest data from the Centers for Disease Control and Prevention.

The XBB variant, which accounted for only 11% of COVID cases in the region just two weeks ago, now makes up over half of all cases (52.6%). That's far higher than the 18% of cases XBB accounts for across the entire U.S.

BQ.1.1 subvariant accounts for 19.7% of COVID cases in New England, and BQ.1 another 16.9%.

"The sudden increase in XBB is pretty striking," Dr. Shira Doron of Tufts Medical Center said. "I wasn't expecting it because it had been smoldering on the chart for a while."

"I think it's like we've been seeing essentially since last December or January, that subvariants of omicron continue to emerge," added Dr. Daniel Kuritzkes of Brigham and Women's Hospital. "Each one that replaces the previous one is doing so either because it is more transmissible or because it is able to evade the immune response generated by the previous variant, which is more or less what viruses tend to do overall."

The good news, they said, is that other than the initial omicron wave a year ago, there really haven't been any other huge surges despite the emergence of these new subvariants.

How effective are COVID boosters against these omicron subvariants?

The omicron subvariants that have become dominant in recent months present a serious threat to the effectiveness of the new boosters, render antibody treatments ineffective and could cause a surge of breakthrough infections, according to a new study.

The XBB, BQ.1 and BQ.1.1 subvariants are the most immune evasive variants of COVID-19 to date, according to scientists affiliated with Columbia University and the University of Michigan.

The scientists, in a study published online earlier this month in the peer-reviewed journal Cell, found that these subvariants are "barely susceptible to neutralization" by the vaccines, including the new omicron boosters. The immune response of people who were vaccinated and had breakthrough infections with prior omicron variants also was weaker against the subvariants.

What are the symptoms of the omicron subvariants?

The symptoms of the latest omicron subvariants are mostly similar to those of the earlier version of omicron, according to NBC News.

Typical symptoms of the omicron subvariants include:

• Sore throat
• Hoarse voice
• Cough
• Fatigue
• Nasal congestion
• Runny nose
• Headache
• Muscle aches 

Unlike earlier variants like delta that affected the lungs, omicron and its subvariants tend to cause more upper respiratory symptoms, doctors say. Those symptoms can include congestion, sore throat and changes in taste and smell.

COVID numbers rising in Mass.

Here in Massachusetts, COVID infections and hospitalizations have been increasing steadily since last month. State health officials reported 9,216 new cases last week, up from 8,391 the previous week. The state's seven-day average positivity also rose to 9.58% Thursday, compared to 8.68% a week earlier.

COVID wastewater data from the Massachusetts Water Resources Authority has also been rising, with the levels the highest they have been since last winter.

Risk levels across much of New England are also starting to creep up, with almost all of Massachusetts now in the medium risk category and Hampden County listed as high risk. And as cases continue to rise, Boston school and city officials are even considering bringing back a mask mandate.

And it's not just COVID that's putting pressure on local hospitals right now.

"There's a lot circulating out there and that's why it's important for people to realize that there are many things you can catch beyond COVID, RSV and influenza," Dr. Daniel Kuritzkes of Brigham and Women's Hospital said. "Although for the most part, they're much less likely to cause any kind of medically serious illness."

Some health experts say that what they're seeing is unprecedented.

"I have been in and around emergency room departments for well over 30 years and have not seen anything along these lines before," Dr. David Clark of Jersey Shore University Medical Center in New Jersey told NBC News.

"The big unknown for us at this point is what kind of [COVID-19] season are we going to have," said another health expert. "Obviously we had two very difficult winters in the past two years. Now I think we have to brace for that."

NBC News and CNBC contributed to this report.