The coronavirus mutant that is now prevalent in the United States is an omicron family member, but scientists say it spreads faster than omicron predecessors, is adept at evading immunity, and may cause more serious disease.

Why? Because it combines omicron and delta properties, it was the nation’s dominant variant in the middle of last year.

A genetic trait known as a “delta mutation” that dates back to the pandemic appears to allow the virus to “escape pre-existing immunity from vaccination and prior infection, especially if you were infected during the omicron wave,” according to Dr. Wesley Long, a pathologist at Houston Methodist in Texas. Because the original omicron strain that swept the world lacked the mutation.

The omicron “subvariant” gaining traction in the United States — known as BA.2.12.1 and responsible for 58 percent of COVID-19 cases in the United States last week — isn’t the only one affected by the delta mutation. The genetic change is also present in the omicron relatives known as BA.4 and BA.5, which dominate in South Africa. Those have the same mutation as delta, while BA.2.12.1 has a nearly identical mutation.

This genetic change is bad news for people who caught the original omicron and assumed they wouldn’t get COVID-19 again anytime soon. Although most people are unsure which variant caused their illness, the original omicron was responsible for a large number of cases late last year and early this year.

According to Long, laboratory data suggests that a prior infection with the original omicron is not very protective against reinfection with the new mutants, though the true risk of reinfection, regardless of variant, is unique to each person and situation.

However, those who have previously been sickened by delta may have some extra armor to ward off the new mutants. Researchers at Ohio State University discovered that COVID patients in intensive care with delta infections induced antibodies that were more effective at neutralizing the new mutants than patients who caught the original omicron.

“The omicron infection antibody does not appear to protect well against the subvariants when compared to delta,” said Dr. Shan-Lu Liu, a study author and co-director of Ohio State’s viruses and emerging pathogens program.

However, according to Liu, the level of protection provided by a delta infection is partly dependent on how long someone was ill. This is because immunity deteriorates over time.

People who became ill with delta should not consider themselves immune to the new subvariants, especially if they are unvaccinated, according to Long. “I don’t think anyone is safe.”

Is there one bright spot? Booster shots, according to Liu, can provide effective protection against the new mutants. Vaccines and prior infection, in general, can protect people from the worst effects of COVID-19. At this point, scientists say it’s too early to tell if the new mutant strain spreading in the United States will result in a significant increase in new cases, hospitalizations, and deaths.

Scientists are still trying to determine how dangerous these new mutants are. Long stated that he has not seen anything that answers that question for him, but Liu stated that emerging data points to more serious illness. According to Liu, the subvariants have properties that indicate they spread more efficiently cell to cell.

The new mutants do not appear to be less virulent than previous versions of omicron, according to Dr. Eric Topol of Scripps Research Translational Institute, and whether they are more virulent or not “will become clear in the months ahead.”

Meanwhile, scientists anticipate that the latest powerhouse mutants will spread quickly because they are more transmissible than their predecessors.

Though home testing makes tracking all COVID cases in the United States difficult, data from Johns Hopkins University shows that cases are averaging nearly 107,000 per day, up from about 87,000 two weeks ago. According to the Centers for Disease Control and Prevention, new hospital admissions of COVID-19 patients have been trending upwards since around mid-April.