VOA慢速英语2021--我们怎么知道什么时候达到群体免疫?

How Will We Know When We Reach Herd¹ Immunity²?

How will we know when we reach herd immunity?

That is the question people are asking as governments race to vaccinate³ people around the world to stop the spread of COVID-19.

Herd immunity is when a large number of people in a community will either have recovered from infection or been vaccinated⁴. Herd immunity does not mean everyone is protected from the virus. It means that the coronavirus can no longer spread easily, helping⁵ to protect those who are at risk.

Once people are sick or receive the vaccine⁶, they start to develop antibodies. Experts think the number of people with antibodies needs to reach 70 percent or more for herd immunity.

However, the virus is always changing and developing into new variants⁸. Health officials are now concerned with variants first discovered in Britain, South Africa and Brazil spreading around the world.

How do you calculate the percentage of people who need to be immune?

Finding how many people, on average, catch the virus from one infected person is important to understanding herd immunity.

Dr. Walter Orenstein is an infectious disease expert at Emory University. He said the percentage of people who need to be immune depends on a number of things. The number could be different depending on where you live. But it is not an exact number.

"It's not 64.9 is terrible and 70.1 is fantastic," he said.

How do we know when we have reached herd immunity?

Experts say there will not be a big announcement.

The evidence will come when there is a large decrease in new infections and fewer people need to go to the hospital for treatment.

The numbers will be different depending on what part of the world you are in.

For example, in India, scientists believe more people will need to be protected from the virus in cities than those who live in rural areas. The virus spreads easier and faster in densely⁹ populated cities.

India is working to find out how many of its 1.4 billion people already have recovered from the virus. And if current vaccines¹⁰ work well against the virus, fewer people will need to be vaccinated to reach herd immunity.

How will the virus variants affect herd immunity?

If vaccines or antibodies from past infections protect people from getting sick again, the fast-spreading variants are not a big concern.

However, if current vaccines are less effective against the variants, drug makers¹¹ will have to update the shots to make them more effective. And even more people will need to be vaccinated.

Scientists are also worried about vaccinating¹² people as quickly as possible to prevent new variants from developing.

Does herd immunity need to be global?

Yes, it is important to reach herd immunity around the world. But some parts of the world will struggle with the coronavirus longer than in others.

The World Health Organization said herd immunity will probably not happen around the world this year. That is because rich nations have reserved most of the vaccines that will be produced in 2021. Poor countries will have to wait longer.

Experts say the virus will never completely come to an end because different countries will have different vaccination¹³ levels.

Can herd immunity wear off?

Experts think immunity from earlier infection or a vaccine should last several months. But it is likely we will need follow-up shots, known as boosters, in the future.

The seasonal¹⁴ flu viruses are changing all the time. That is why people need a flu shot each year. The coronavirus is also changing but not as easily. So it is possible people will probably not need a COVID-19 shot every year.

What if the vaccines do not keep people from getting sick?

The current vaccines, from Pfizer-BioNTech and Moderna, seem to work very well. They do prevent people from getting sick.

It is not clear, however, how well they stop the virus from moving from person to person. But experts say they should help to reduce the spread of the virus.

Deborah Fuller is a vaccine expert at the University of Washington. She said the vaccines should limit the amount of time people can spread the virus to others if they do get sick.

Words in This Story

variant⁷ - n. something that is different in some way from others of the same kind

immunity - n. the power to keep yourself from being affected¹⁵ by a disease

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

update - v. to change (something) by including the most recent information

flu - n. a common disease that is caused by a virus and that causes fever, weakness, body aches, and breathing problems

1 herd   

n.兽群，牧群；vt.使集中，把…赶在一起

参考例句：

• She drove the herd of cattle through the wilderness.她赶着牛群穿过荒野。
• He had no opinions of his own but simply follow the herd.他从无主见，只是人云亦云。

2 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。

3 vaccinate   

vt.给…接种疫苗；种牛痘

参考例句：

• Local health officials then can plan the best times to vaccinate people.这样，当地的卫生官员就可以安排最佳时间给人们接种疫苗。
• Doctors vaccinate us so that we do not catch smallpox.医生给我们打预防针使我们不会得天花。

4 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？

5 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

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 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。

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 densely   

ad.密集地；浓厚地

参考例句：

• A grove of trees shadowed the house densely. 树丛把这幢房子遮蔽得很密实。
• We passed through miles of densely wooded country. 我们穿过好几英里茂密的林地。

10 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。

11 makers   

n.制造者，制造商（maker的复数形式）

参考例句：

• The makers of the product assured us that there had been no sacrifice of quality. 这一产品的制造商向我们保证说他们没有牺牲质量。
• The makers are about to launch out a new product. 制造商们马上要生产一种新产品。 来自《简明英汉词典》

12 vaccinating   

给…接种疫苗( vaccinate的现在分词 )； 注射疫苗，接种疫苗

参考例句：

• At first blush, vaccinating the wolves against rabies seems a simple solution. 乍一看来，为狼群注射防狂犬病疫苗是一种简单的办法。
• Also vaccinating children against misers (measles) has saved many lives. 还有，给儿童进行疫苗接种防止麻疹也挽救了许多生命。

13 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。

14 seasonal   

adj.季节的，季节性的

参考例句：

• The town relies on the seasonal tourist industry for jobs.这个城镇依靠季节性旅游业提供就业机会。
• The hors d'oeuvre is seasonal vegetables.餐前小吃是应时蔬菜。

15 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。