(NEXSTAR) – The omicron variant of COVID-19 has once again evolved, spawning new versions of itself with slight mutations that could make the virus more transmissible or more dangerous.

With each new subvariant comes a new mixture of letters and numbers. BA.5 is still the dominant variant in the U.S., according to the latest data from the Centers for Disease Control and Prevention, but two new subvariants are rising up the ranks: BQ.1 and BQ.1.1.

There’s also XBB, a subvariant spreading rapidly in other countries, that’s causing some concern.

It’s a lot to keep track of, admittedly. Here’s what you need to know.

What are BQ.1 and BQ.1.1? Where are they spreading?

Both subvariants are still types of omicron, the variant that spread like wildfire through the U.S. last winter and has remained dominant since.

BQ.1 makes up about 9% of cases nationwide and BQ.1.1 makes up about 7% of cases, according to the CDC. They’re still a minority of cases, but are growing fast, at a rate the White House’s chief medical adviser Dr. Anthony Fauci recently called “pretty troublesome.”

In addition to nationwide numbers, the CDC also tracks variants by geographic region. The region made up of New York, New Jersey, Puerto Rico and the Virgin Islands have the highest proportions of BQ.1 and BQ.1.1 cases.

What do we know about the so-called “nightmare variant,” XBB?

The XBB subvariant of omicron has been identified in 26 countries, according the World Health Organization, and is spreading most quickly in Southeast Asia. Very few cases have been detected in the U.S. so far.

XBB has earned itself the hyperbolic nickname of “nightmare variant” because it appears to be better at evading people’s existing immunity to COVID-19.

“Available preliminary laboratory-based evidence suggests that XBB is the most antibody-evasive SARS-CoV-2 variant identified to date,” the WHO said last week.

However, while it shows signs of spreading quicker than past subvariants, the WHO said there is no evidence yet that it leads to more severe disease. All types of omicron we’ve seen so far have generally been less deadly than the delta variant we saw in the summer of 2021, especially for those vaccinated against the virus.

Are the new subvariants more contagious? Do the vaccines work against these subvariants?

Thanks to mutations on the virus’ spike protein, all three appear to be more contagious than BA.5, the current dominant strain of omicron – that’s precisely how they gain ground as they compete against other mutations for survival, explained Dr. Monica Gandhi, professor of medicine and infectious disease expert at the University of California, San Francisco.

“Often, as we’ve seen these variants emerge, they also have a lot of mutations in their spike protein, which is of course the place where we have designed our vaccines against, unfortunately,” said Gandhi. “So because of that, they tend to evade antibodies.”

While these mutations may be immune-evasive, your antibodies and existing immunity aren’t totally useless, Gandhi reassured. The variants may skirt the immunity that prevents mild infections, but vaccines (or even better, vaccines plus a past infection) are both very effective at preventing serious illness and death.

Older people in particular, should seek out the newest booster – a bivalent vaccine that combines the ancestral strain of COVID-19 with the newer omicron strain – to get the most up-to-date protection, Gandhi said.