The coronavirus mutant now dominant in the United States is a member of the omicron family. Still, scientists say it spreads faster than its omicron predecessors, is adept at escaping immunity, and could potentially cause more serious illness.
Why? Because it combines features of both omicron and delta, the dominant variety of the country in the middle of last year.
A genetic trait harking back to the past of the pandemic, known as a “delta mutation,” appears to allow the virus “to escape pre-existing immunity to vaccination and previous infection, especially if you were infected in the omicron-wave,” said Dr. Wesley Long, a pathologist at Houston Methodist in Texas. That’s because the original omicron strain that swept the world didn’t have the mutation.
The omicron “subvariant” gaining ground in the U.S. — known as BA.2.12.1 and responsible for 58% of US COVID-19 cases last week — isn’t the only one affected by the delta mutation. The genetic change is also present in the omicron relatives that dominate together in South Africa, known as BA.4 and BA.5. They have exactly the same mutation as delta. In contrast, BA.2.12.1 has one that is almost identical.
This genetic change is bad news for people who caught the original omicron and thought they were unlikely to get COVID-19 again soon. While most people aren’t sure which variant caused their disease, the original omicron caused a massive wave of cases late last year and early this year.
Long said lab data suggest that a previous infection with the original omicron isn’t very protective against reinfection with the new mutants. However, regardless of variant, the real risk of being reinfected is unique to each person and situation.
In a twist, those who were previously sick of the delta can have some extra armor to fend off the new mutants. A study released before being reviewed by other scientists, by Ohio State University researchers, found that COVID patients in intensive care with delta infections induced antibodies that could neutralize the new mutants better than patients given the original omicron.
“The omicron infection antibody does not appear to protect well against the subvariants compared to delta,” said Dr. Shan-Lu Liu, a study author who co-directs the Ohio State Virus and Emerging Pathogen Program.
But Liu said the level of protection a delta infection provides depends partly on how long a person has been sick. That’s because immunity wanes over time.
People who got sick from delta shouldn’t consider themselves invulnerable to the new subvariants, especially if they haven’t been vaccinated, Long said. “I wouldn’t say anyone is safe.”
At this point, scientists say it’s too early to know whether the new mutant gaining ground in the U.S. will cause a significant rise in recent cases, hospitalizations, and deaths. A bright spot? Booster shots can provide strong protection against the new mutants, Liu said. Overall, vaccines and previous infections can protect people from the worst effects of COVID-19.
Scientists are still trying to figure out how virulent these new mutants are. Long said he hasn’t seen anything that answers that question, but Liu said emerging data points to a more serious illness. Liu said the subvariants have properties that suggest they spread more efficiently from cell to cell.
The virus “just hides inside the cell and spreads through cell-to-cell contact,” Liu said. “That’s scarier because the virus doesn’t come out for the antibody to work.”
Dr. Eric Topol, head of the Scripps Research Translational Institute, said the new mutants certainly appear no less virulent than previous versions of omicron, and whether they are more virulent or not “will become clear in the coming months.”
Meanwhile, scientists expect the latest powerhouses to spread quickly, as they are more portable than their predecessors.
While home testing makes it difficult to track all U.S. COVID cases, data from Johns Hopkins University shows an average of nearly 107,000 points per day, up from about 87,000 two weeks ago. And according to the Centers for Disease Control and Prevention, there has been an upward trend in new hospitalizations of patients with COVID-19 since mid-April.
“I’m hopeful that we don’t see a similar increase in hospitalizations as in previous waves,” Long said. “But with COVID, every time a lot of people are infected, it’s just a numbers game. Some of those people will be serious. Some of those people need to be hospitalized. Some of them will sadly die.”
The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute’s Department of Science Education. The A.P. is solely responsible for all content.