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The new Omicron variant¹ has already shown how easily it infects people. But scientists do not yet know if it also causes more severe disease.

"Everything is riskier² now because Omicron is so much more contagious³," said Dr. S. Wesley Long. He heads the testing lab at Houston Methodist Hospital.

Omicron now is the number one variant in the United States, health officials said Monday. About three-quarters of new infections last week were from Omicron.

Public health officials are surprised at how quickly Omicron became the number one cause of COVID-19 infection. After just three weeks, Omicron makes up 80 percent of new symptomatic cases found by Houston Methodist. Long said it took the Delta⁴ variant three months to reach that level.

The variant has come at a bad time. Travel is increasing for the holidays, and people have started gathering⁵. But what the arrival of Omicron will mean for the world is still unclear.

Here is the latest on what is known and what is still to learn about Omicron:

How much protections do vaccines⁷ provide?

Vaccines in the U.S. and around the world do not offer as much protection against Omicron as they have against other variants⁸. But vaccines still help a lot.

And lab tests show that two shots may not be strong enough to prevent infection. But a booster shot of either the Pfizer or Moderna vaccine⁶ can fight off Omicron.

Antibodies produced by the vaccine naturally drop over time. The booster shot raises them back up again. But it is unclear how many antibodies are needed to fight off Omicron. The booster provides 20 percent less protection against an Omicron infection than a Delta infection, said Dr. Egon Ozer of Northwestern University.

But experts say that while the virus may infect someone who has been vaccinated⁹, the booster protects against severe infection.

"The vaccines are going to protect you against severe disease, hospitalization and death," said Long. "And that's really the most important thing."

Natural Immunity¹⁰?

Having already suffered a COVID-19 infection does not appear to offer much protection against Omicron. However, as with vaccination¹¹, it may reduce the chances of severe illness.

In South Africa, Omicron has already spread widely. Scientists reported a jump in reinfections that they had not seen from the two previous variants.

In Britain, a report from the Imperial College of London on Friday found the risk of reinfection from Omicron was five times higher compared to the earlier Delta variant.

Health experts say anyone who has had COVID-19 still should get vaccinated.

Why does Omicron spread so fast?

Scientists are trying to figure out what makes Omicron so contagious.

Researchers in Hong Kong recently reported that Omicron may spread more quickly in the lungs than Delta spread, but it does not spread as deep in the lungs as Delta.

What scientists cannot measure is human behavior. Many places have been easing pandemic restrictions¹², which has helped the virus to spread. Also, winter has forced gatherings¹³ indoors, and travel has increased just as Omicron began spreading.

Is Omicron causing milder illness?

Scientists say it is still too early to know if Omicron is milder, especially because there have been so many breakthrough infections. However, if a vaccinated person gets infected, it should be a milder illness than if an unvaccinated person gets infected from Omicron.

Early reports from South Africa suggested milder illness. But doctors were unsure whether that is because the population is younger. The British study also found no evidence that Omicron has been milder than Delta, even in young adults.

Dr. Jacob Lemieux researches variants for a group led by Harvard Medical School. "There's a hint, and I think many of us are hopeful, that Omicron will be less severe," he said.

Who is most at risk?

Based on other variants, scientists think that older people, and those with underlying¹⁴ health conditions are more likely to have severe disease.

"I don't think it's going to be any different" than other variants, said Dr. Carlos del Rio of Emory University.

During the holidays, experts agree that in addition to getting vaccinated and boosted, people should take basic safety measures: wear face coverings, avoid crowds, and practice social distancing.

Words in This Story

variant — n. something that is different in some way from others of the same kind

contagious — adj. able to be passed from one person or animal to another by touching¹⁵

booster — n. an additional amount of something that strengthens an earlier treatment, such as a vaccination

antibody — n. a substance produced by the body to fight disease

hint — n. a small piece of information that helps you guess an answer or do something more easily

1 variant   

adj.不同的，变异的；n.变体，异体

参考例句：

• We give professional suggestions according to variant tanning stages for each customer.我们针对每位顾客不同的日晒阶段，提供强度适合的晒黑建议。
• In a variant of this approach,the tests are data- driven.这个方法的一个变种，是数据驱动的测试。

2 riskier   

冒险的，危险的( risky的比较级 )

参考例句：

• Now they are starting to demand higher returns on riskier assets. 而今他们开始在风险更高的资产上要求更高的回报。
• The problem with that: RIM's business is getting riskier every quarter. 不过问题也随之而来：RIM面临的业务风险正逐季增大。

3 contagious   

adj.传染性的，有感染力的

参考例句：

• It's a highly contagious infection.这种病极易传染。
• He's got a contagious laugh.他的笑富有感染力。

4 delta   

n.（流的）角洲

参考例句：

• He has been to the delta of the Nile.他曾去过尼罗河三角洲。
• The Nile divides at its mouth and forms a delta.尼罗河在河口分岔，形成了一个三角洲。

5 gathering   

n.集会，聚会，聚集

参考例句：

• He called on Mr. White to speak at the gathering.他请怀特先生在集会上讲话。
• He is on the wing gathering material for his novels.他正忙于为他的小说收集资料。

6 vaccine   

n.牛痘苗，疫苗；adj.牛痘的，疫苗的

参考例句：

• The polio vaccine has saved millions of lives.脊髓灰质炎疫苗挽救了数以百万计的生命。
• She takes a vaccine against influenza every fall.她每年秋季接种流感疫苗。

7 vaccines   

疫苗，痘苗( vaccine的名词复数 )

参考例句：

• His team are at the forefront of scientific research into vaccines. 他的小组处于疫苗科研的最前沿。
• The vaccines were kept cool in refrigerators. 疫苗放在冰箱中冷藏。

8 variants   

n.变体( variant的名词复数 )；变种；变型；（词等的）变体

参考例句：

• Those variants will be preserved in the'struggle for existence". 这些变异将在“生存竞争”中被保留下来。 来自辞典例句
• Like organisms, viruses have variants, generally called strains. 与其他生物一样，病毒也有变种，一般称之为株系。 来自辞典例句

9 vaccinated   

[医]已接种的，种痘的，接种过疫菌的

参考例句：

• I was vaccinated against tetanus. 我接种了破伤风疫苗。
• Were you vaccinated against smallpox as a child? 你小时候打过天花疫苗吗？

10 immunity   

n.优惠；免除；豁免，豁免权

参考例句：

• The law gives public schools immunity from taxation.法律免除公立学校的纳税义务。
• He claims diplomatic immunity to avoid being arrested.他要求外交豁免以便避免被捕。

11 vaccination   

n.接种疫苗，种痘

参考例句：

• Vaccination is a preventive against smallpox.种痘是预防天花的方法。
• Doctors suggest getting a tetanus vaccination every ten years.医生建议每十年注射一次破伤风疫苗。

12 restrictions   

约束( restriction的名词复数 )； 管制； 制约因素； 带限制性的条件（或规则）

参考例句：

• I found the restrictions irksome. 我对那些限制感到很烦。
• a snaggle of restrictions 杂乱无章的种种限制

13 gatherings   

聚集( gathering的名词复数 )； 收集； 采集； 搜集

参考例句：

• His conduct at social gatherings created a lot of comment. 他在社交聚会上的表现引起许多闲话。
• During one of these gatherings a pupil caught stealing. 有一次，其中一名弟子偷窃被抓住。

14 underlying   

adj.在下面的，含蓄的，潜在的

参考例句：

• The underlying theme of the novel is very serious.小说隐含的主题是十分严肃的。
• This word has its underlying meaning.这个单词有它潜在的含义。

15 touching   

adj.动人的，使人感伤的

参考例句：

• It was a touching sight.这是一幅动人的景象。
• His letter was touching.他的信很感人。