新冠病毒变种在美国传播

Medical experts say the most dominant form of COVID-19 currently spreading in the United States appears to spread faster than earlier variants, or versions. In addition, it might be better at escaping immunity and could cause more serious disease.

Scientists say the "subvariant" now spreading is a mutation genetically linked to both the Omicron and Delta versions of COVID-19. Both of those versions were dominant in the U.S. in the past. The new virus form has a genetic quality that comes from the pandemic's past. It is known as a "Delta mutation."

Dr. Wesley Long is an infectious disease expert at Houston Methodist in Texas. He said it appears to permit the virus "to escape pre-existing immunity from vaccination and prior infection, especially if you were infected in the Omicron wave." The mutation is believed to be able to better escape immunity because the past Omicron variant did not have it.

The current variant spreading in the U.S., known as BA.2.12.1, was responsible for about 58 percent of U.S. COVID-19 infections one week ago.

There are other kinds of Omicron viruses that have the mutation. Two in South Africa, known as BA.4 and BA.5, have the same genetic mutation as delta. And BA.2.12.1 has one that is nearly the same.

This genetic change may trouble people who caught the first Omicron version and thought it made them unlikely to get COVID-19 again soon. Most people do not know for sure which kind of coronavirus caused their illness. But the first Omicron version caused a huge wave of cases late last year and early this year.

Long said laboratory data suggests that an earlier infection with the first Omicron is not very protective against reinfection with the new mutations. However, one study by researchers at Ohio State University found those who had Delta may have some immunity against the new viruses.

Dr. Shan-Lu Liu co-wrote the study. He said the amount of protection a Delta infection provides depends partly on how long ago someone was sick. That is because immunity decreases over time.

Long advises that people who got sick with Delta should not think of themselves as completely protected against the new subvariants, especially if they are not vaccinated. He said, "I wouldn't say anyone is safe."

Liu said booster shots can provide strong protection against the new kinds of COVID-19. In general, vaccines and past infection can protect people from the worst outcomes of COVID-19. But Liu added that early data point toward more serious disease with the new mutants. Scientists say it is too early to know if the versions will lead to a higher rate of hospitalizations and deaths.

Though home testing makes it difficult to follow all U.S. COVID cases, data from Johns Hopkins University show they are averaging nearly 107,000 a day. That is up from 87,000 two weeks ago. And the Centers for Disease Control and Prevention (CDC) found that the number of people entering the hospital with COVID-19 has been increasing since around mid-April.

Long said, "I'm hopeful that we don't see a similar increase in hospitalizations that we've had in prior waves." He added, "But with COVID, any time you have lots of people being infected, it's just a numbers game. Some of those people are going to be severe. Some of those people are going to need hospitalization. Some of them, unfortunately, are going to pass away."

I'm Gregory Stachel.

The Associated Press reported this story. Greg Stachel adapted the story for Learning English.

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dominant – adj. the main or most important

immunity – n. to be protected against catching a disease

mutate – v. to cause (a gene) to change and create an unusual characteristic in a plant or animal

prior – adj. existing earlier in time

booster shot – n. an extra amount of a substance (called a vaccine) that is injected with a needle into a person or animal to help protect against a particular disease

unfortunately – adv. used to say that something bad or unlucky has happened

pass away – v. to die

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