The future of the pandemic is looking clearer as we learn more about infection

The future of the pandemic is looking clearer as we learn more about infection

Transcript²

SARS-CoV-2 is shown in this colorized transmission electron micrograph. This specimen³ was isolated⁴ from a patient in the U.S. Particles of the virus are shown emerging from the surface of cells cultured in the lab.

Science Source

During the early days of the pandemic, scientists and doctors were concerned that being infected with SARS-CoV-2 might not trigger a strong immune response in many people – thus an infection might not provide long-term protection.

"Immunity⁵ to Covid-19 could be lost in months, UK study suggests," a headline from The Guardian⁶ alerted back in July 2020. "King's College London team found steep drops in patients' antibody levels three months after infection," the story warned.

But that idea was based on preliminary data from the laboratory — and on a faulty understanding of how the immune system works. Now about a year and a half later, better data is painting a more optimistic picture about immunity after a bout¹ of COVID-19. In fact, a symptomatic infection triggers a remarkable⁷ immune response in the general population, likely offering protection against severe disease and death for a few years.

And if you're vaccinated⁸ on top of it, your protection is likely even better, studies are consistently showing.

Here are several key questions people have been asking throughout the pandemic – and ones that researchers are beginning to answer.

If I just had COVID, am I protected against getting a severe course of COVID in the future ?

With SARS-CoV-2, your immune system generates two types of protection: protection against reinfection and protection against severe illness upon that second infection.

If you're under age 50 and healthy, then a bout of COVID-19 offers good protection against severe disease if you were to be infected again in a future surge, says epidemiologist Laith Abu-Raddad, at Weill-Cornell Medical-Qatar. "That's really important because eventually, every one of us will get infected," he says. "But if reinfections prove to be more mild, in general, it will allow us to live with this pandemic in a much easier way."

Abu-Raddad and his team have been tracking reinfections in Qatar for more than a year. In one study, the team analyzed⁹ about 1,300 reinfections among more than 350,000 people in Qatar. They found that a prior COVID-19 infection reduced the risk of hospitalization upon reinfection by about 90% compared with in people having their first infection.

These findings, published in the New England Journal of Medicine in December, are consistent with data released by the Centers for Disease Control and Prevention last month. In that study, a prior infection reduced the risk of hospitalization during the delta¹⁰ surge by more than 50 times compared with in people who hadn't had a prior infection and were not vaccinated. People who had had both a prior infection and were vaccinated had the most protection.

And here's the "really good news," Abu-Raddad says: This protection against severe disease persists, perhaps for years. "We've been following this same group of people for over a year and a half now, we don't see much waning¹¹. If it's there, it's too small to discern."

But the good news doesn't necessarily hold true for everyone. This long-term protection is seen in healthy people under age 50, Abu-Raddad points out. It's likely less potent¹² and possibly more short-lived for people who are older or who have underlying¹³ health conditions, he says. More data is needed to know how the protection varies with age.

That said, studies in the laboratory also suggest that protection against severe disease is long term after a bout of COVID-19, at least for healthy people.

In particular, antibodies against SARS-CoV-2 persist in the blood for months, possibly years after an infection, scientists at the Fred Hutchinson Cancer Research Center and Emory University have reported.

In that study, immunologist Juliana McElrath and her colleagues measured antibodies in the blood of more than 200 people after a confirmed SARS-CoV-2 infection. More than 90% of the volunteers generated antibodies to SARS-CoV-2 right after the infection. In general, the level of antibodies declined quickly two to three months after an infection, but after about four months, the level began to plateau. Even after eight months, the vast majority of people in the study still had antibodies in their blood that could neutralize¹⁴ SARS-CoV-2.

After publishing that study in Cell Reports Medicine, the team continued to follow these same people, and the team now has data up to 15 months after the infection, the researchers told Nature on Tuesday. So far, the antibodies seem to be sticking around for the long haul, said immunologist Rafi Ahmed at Emory University, who helped to lead the study. "Looking at the shape of the curve, it looks pretty damn good. It is really quite stable."

Last Tuesday, researchers at the Johns Hopkins Medical Institutions also reported that SARS-CoV-2 antibodies can persist up to 20 months. In that study, 293 out of 295 unvaccinated people generated antibodies after a positive COVID test.

This pattern, with antibodies declining quickly and then plateauing, occurs with any infection, not just SARS-CoV-2, immunologist Deepta Bhattacharya told NPR back in August. "In every single immune response, there is a sharp rise in antibodies, a period of sharp decline," and then it starts to stabilize¹⁵ at a lower level.

About six months after a SARS-CoV-2 infection, right around the time when the antibody level starts to stabilize, the immune system does something extraordinary: It generates special cells, called long-lived plasma¹⁶ cells, that can make potent antibodies against SAR-CoV-2, for decades, possibly even a lifetime. "These cells are remarkable," Bhattacharya said. "They're estimated to spit out something like 10,000 antibody molecules¹⁷ per second." Therefore, you wouldn't need many of these cells to protect against a future infection.

On top of that, the immune system also generates several types of cells, known as B and T cells, which kick into action upon reinfection. These cells quickly ramp¹⁸ up antibody levels and destroy infected cells to ensure a mild course of COVID doesn't turn into a serious one. Several studies, including one published in January, have shown that these cells are durable¹⁹ and likely persist longer than year.

Does this mean I won't get reinfected if I've had COVID or even better, have had COVID and am fully²⁰ vaccinated?

Unfortunately, the answer is no.

"Reinfections are not just possible, they're pretty much inevitable," says evolutionary²¹ biologist Jeffrey Townsend at Yale University. "At least all the evidence that we have now says that that's true."

To estimate how often reinfections will occur with SARS-CoV-2, Townsend and his team have been studying four other coronaviruses. They are known as "seasonal²² coronaviruses" and cause about 30% of colds each year.

"They all infect and reinfect on a yearly timescale," he says, "so there's no reason to expect something different from SARS-CoV-2."

The risk of reinfection is likely very low right after you're sick — up to about four months or so afterwards, Townsend and his team estimate. Then the risk grows. And their data suggest that, on average, people will be reinfected every year or two with SARS-CoV-2. "It is very rare for reinfection to happen on a very short timescale, but on a longer timescale, it seems to happen with some frequency," he says.

But your specific risk for reinfection depends heavily on your personal situation, such as whether you're exposed to lots of people at work or live with children who go to school. "So that time frame for reinfection each year or so assumes that we all just relax everything about our protections and just sort of let it rip, basically," Townsend says.

And, he says, your risk of reinfection also depends on the virus and how much it mutates. For example, during the delta surge, a previous infection offered about 85% protection against reinfection, Laith Abu-Raddad and his team found. But with omicron that protection dropped to 55%. So the chance of reinfection was much higher.

So why is the immune system so good at preventing severe disease but not really able to stop reinfection?

No one knows for sure. But this strategy may be a deliberate one by the immune system, immunologist Jonathan Yewdell explained last week on the podcast This Week In Virology.

In essence, your immune system is allocating²³ resources. And its primary goal is to keep you alive. So the immune system has decided²⁴ that, with coronaviruses, it's not worth stopping the infection as long as it can stop serious, life-threatening illness.

"That is good enough under most circumstances," Yewdell, who's at the National Institutes of Health, explained. "You might not think when you're in bed with 106 [degree] fever, you know, and crying for your spouse²⁵ to help you because you could barely move that 'this is good enough.' But as long as you've recovered ... you know, mission accomplished²⁶."

In other words, the immune system is not built to stop every sickness or asymptomatic infection. And it's definitely not built to "give you a negative PCR test," Yewdell says.

So the future of COVID-19 is starting to become clearer: We're going to have a lot more infections but hopefully a lot fewer hospitalizations and deaths.

Editor's note: Yewdell's point about the possible severity of illness figures into the answer to the question: Should you deliberately²⁷ try to get COVID-19? To read more, see this story.

1 bout   

n.侵袭，发作；一次(阵，回)；拳击等比赛

参考例句：

• I was suffering with a bout of nerves.我感到一阵紧张。
• That bout of pneumonia enfeebled her.那次肺炎的发作使她虚弱了。

2 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

3 specimen   

n.样本，标本

参考例句：

• You'll need tweezers to hold up the specimen.你要用镊子来夹这标本。
• This specimen is richly variegated in colour.这件标本上有很多颜色。

4 isolated   

adj.与世隔绝的

参考例句：

• His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
• Patients with the disease should be isolated. 这种病的患者应予以隔离。

5 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。

6 guardian   

n.监护人；守卫者，保护者

参考例句：

• The form must be signed by the child's parents or guardian. 这张表格须由孩子的家长或监护人签字。
• The press is a guardian of the public weal. 报刊是公共福利的卫护者。

7 remarkable   

adj.显著的，异常的，非凡的，值得注意的

参考例句：

• She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
• These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

8 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？

9 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

10 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。

11 waning   

adj.（月亮）渐亏的，逐渐减弱或变小的n.月亏v.衰落( wane的现在分词 )；（月）亏；变小；变暗淡

参考例句：

• Her enthusiasm for the whole idea was waning rapidly. 她对整个想法的热情迅速冷淡了下来。
• The day is waning and the road is ending. 日暮途穷。 来自《现代汉英综合大词典》

12 potent   

adj.强有力的，有权势的；有效力的

参考例句：

• The medicine had a potent effect on your disease.这药物对你的病疗效很大。
• We must account of his potent influence.我们必须考虑他的强有力的影响。

13 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。

14 neutralize   

v.使失效、抵消，使中和

参考例句：

• Nothing could neutralize its good effects.没有什么能抵消它所产生的好影响。
• Acids neutralize alkalis and vice versa.酸能使碱中和碱，亦能使酸中和。

15 stabilize   

vt.（使）稳定，使稳固，使稳定平衡；vi.稳定

参考例句：

• They are eager to stabilize currencies.他们急于稳定货币。
• His blood pressure tended to stabilize.他的血压趋向稳定。

16 plasma   

n.血浆，细胞质，乳清

参考例句：

• Keep some blood plasma back for the serious cases.留一些血浆给重病号。
• The plasma is the liquid portion of blood that is free of cells .血浆是血液的液体部分，不包含各种细胞。

17 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

18 ramp   

n.暴怒，斜坡，坡道；vi.作恐吓姿势，暴怒，加速；vt.加速

参考例句：

• That driver drove the car up the ramp.那司机将车开上了斜坡。
• The factory don't have that capacity to ramp up.这家工厂没有能力加速生产。

19 durable   

adj.持久的，耐久的

参考例句：

• This raincoat is made of very durable material.这件雨衣是用非常耐用的料子做的。
• They frequently require more major durable purchases.他们经常需要购买耐用消费品。

20 fully   

adv.完全地，全部地，彻底地；充分地

参考例句：

• The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气，然后全部呼出。
• They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。

21 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• Life has its own evolutionary process.生命有其自身的进化过程。
• These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。

22 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。

23 allocating   

分配，分派( allocate的现在分词 )； 把…拨给

参考例句：

• Administrative practice generally follows the judicial model in allocating burdens of proof. 在分配举证责任方面，行政实践通常遵循司法模式。
• A cyclical multiplexing technique, allocating resources in fixed-time slices. 以固定的时间片分配资源的循环复用技术。

24 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

25 spouse   

n.配偶(指夫或妻)

参考例句：

• Her spouse will come to see her on Sunday.她的丈夫星期天要来看她。
• What is the best way to keep your spouse happy in the marriage?在婚姻中保持配偶幸福的最好方法是什么？

26 accomplished   

adj.有才艺的；有造诣的；达到了的

参考例句：

• Thanks to your help,we accomplished the task ahead of schedule.亏得你们帮忙,我们才提前完成了任务。
• Removal of excess heat is accomplished by means of a radiator.通过散热器完成多余热量的排出。

27 deliberately   

adv.审慎地；蓄意地；故意地

参考例句：

• The girl gave the show away deliberately.女孩故意泄露秘密。
• They deliberately shifted off the argument.他们故意回避这个论点。