You Can Get Covid Twice, But What Are the Odds?

再次感染新冠的概率有多大？

Covid-19 reinfections are more common and can happen within a shorter window of time than doctors previously thought possible

最新研究显示，再次感染新冠的情况比医生们此前预想的更为常见，而且两次感染的间隔时间也比预期更短。

Sumathi Reddy

苏马蒂·瑞迪

There’s a good chance you’ll get Covid more than once.

人们再次感染新冠病毒的几率并不小。

Covid-19 reinfections are more common and can happen within a shorter window of time than doctors previously thought possible, recent research suggests. More than half of people in the U.S. showed signs of having been infected at least once as of February, according to a report Tuesday from the Centers for Disease Control and Prevention.

近期的研究显示，再次感染新冠的情况要比医生们此前预想的更为常见，而且两次感染的间隔时间也比预期更短。根据美国疾病控制与预防中心（Centers for Disease Control and Prevention，简称CDC）4月26日的一份报告，截至今年2月，美国有超过一半人显示出至少感染过一次新冠病毒的迹象。

Data from the U.K. government found that reinfections were 10 times higher during the recent Omicron outbreak compared with the earlier Delta outbreak between May and December last year. People who were unvaccinated, younger and lived in areas the study described as more deprived were more likely to be reinfected between July 2020 and March 2022.

英国政府的数据发现，在最近一轮由奥密克戎引发的疫情中，再次感染的情况要比去年5月至12月德尔塔疫情期间高出10倍。2020年7月至2022年3月间，那些未接种疫苗、更为年轻且居住在研究人员称为较落后地区的人，他们再次感染新冠的几率更大。

Reinfections usually appear to be mild in otherwise healthy people, doctors say. But some reinfections are serious, and it’s not clear what the risk of long Covid might be. People who had a milder first infection with a lower viral load were at higher risk of being reinfected, the U.K. data indicates.

医生们说，身体健康的人再次感染新冠病毒时，似乎通常症状轻微。但也有症状严重的病例，而且不太清楚留下新冠长期后遗症的风险有多大。英国的数据显示，初次感染时病毒载量较低、症状较轻的人，他们再次感染的风险更高。

“On average at a population level, the people who get reinfected have milder symptoms,” says Francois Balloux, an infectious disease epidemiologist and director of the UCL Genetics Institute in London. “That doesn’t mean that some people might not have a worse infection the second or even third time.” 

“在人口层面上平均而言，人们再次感染后，症状会相对更轻微。”传染病流行病学家、伦敦大学学院（University College London）遗传学研究所（Genetics Institute）主任弗朗索瓦·巴洛克斯（Francois Balloux）说，“这并不是说有些人在第二次或第三次感染时，就不会出现更严重的症状。”

Currently in the U.K. about 12% of Covid-19 infections are reinfections, Dr. Balloux says. He expects that number to increase over time and says that it’s likely that the viral dose or number of particles a person is exposed to will influence the symptom severity. 

巴洛克斯博士说，目前在英国，约有12%的新冠感染病例是再次感染。他预计随着时间推移，这一比例还将上升。他还指出，人们在暴露环境中接触到的病毒剂量或颗粒数量可能会影响症状的严重程度。

Scientists are still learning about the frequency and severity of reinfections; much of the research is preliminary so far. The U.S. doesn’t track national reinfection rates broadly. 

眼下，科学家仍在研究再次感染的发生频率以及严重程度；到目前为止，大部分都只是初步研究。美国没有对全国范围内的再感染率进行广泛追踪。

Reinfections can happen within less than three months

在不到三个月内两次感染新冠病毒是可能的

Doctors and health agencies typically say most people are protected from a Covid reinfection for at least 90 days. Your body’s immune defenses typically strengthen after an infection, then wane.

医生和卫生机构通常说，大部分人在初次感染新冠病毒后，至少90天内不会再次感染。经历一次感染后，人体内的免疫屏障往往会得到巩固，随后逐渐减弱。

However, there is evidence that people can get reinfected within shorter periods. 

然而有证据表明，人们会在更短的时间内再次感染。

An April Centers for Disease Control and Prevention report identified 10 people who were reinfected with Covid-19 less than 90 days later. In at least one case, reinfection occurred 23 days later. 

CDC在4月发布的一份报告确认，有10人在上次感染新冠后不到90天内再次感染了这一病毒。至少有一个病例，其两次感染的间隔时间仅为23天。

Researchers in Spain recently presented preliminary results of a study documenting the case of a 31-year-old woman who caught Covid-19 twice within three weeks. The woman, a healthcare worker, was fully vaccinated and received a booster shot 12 days before testing positive for the Delta variant on Dec. 20. She didn’t develop any symptoms the first time she was infected. Twenty days later, she developed a cough and fever and tested positive for the Omicron variant. 

近日，西班牙研究人员公布了一项初步研究结果，该研究记录了一名31岁女性在三周内两度感染新冠的情况。这位女性是一名医护人员，已全程接种新冠疫苗，去年12月20日，也就是她接种加强针的12天后，其新冠检测结果呈阳性，感染毒株为德尔塔。初次感染时，她没有出现任何症状。20天后，她出现咳嗽及发热，随后在检测中发现其感染了奥密克戎。

There is also preliminary evidence that reinfections with the same variant can occur.  A Danish preprint, a study that hasn’t been peer-reviewed, found that reinfection of different subvariants of Omicron are rare but do take place. Among 187 reinfection cases, 47 were people infected with BA.1 and then BA.2 20 to 60 days later, researchers found. The majority of people were young, unvaccinated and had mild symptoms.  There was no difference in severity between their first and second infection.

此外，还有初步证据显示，再次感染同一变异株的情况也会出现。丹麦的一项研究的预印本（指未经同行审阅的研究报告）发现，再次感染奥密克戎不同亚型变异株的情况虽不多见，但确有发生。研究人员发现，在187例再次感染病例中，有47人在感染BA.1的20天至60天后，再次感染BA.2。其中大多数是未接种疫苗的年轻人，且症状轻微。就严重程度而言，他们的两次感染没有差别。

Some reinfections can be serious

一些再次感染病例出现了严重症状

A March preprint looked at more than 300,000 Covid-19 patients in the U.S. VA system. About 9,200 of them tested positive again at least 90 days after their first positive test; 17% of the reinfected patients were hospitalized. Another 189 cases had a third positive test at least 90 days after their second infection and about 26% of them were hospitalized. 

3月份一项研究的预印本分析了美国退伍军人管理局（U.S. Veterans Administration，简称VA）系统中的逾30万名新冠患者。其中约有9,200人在首次检测呈阳性的至少90天后再次检出阳性；再次感染的患者中，有17%住院接受治疗。另有189人在两度感染至少90天后，第三次检出阳性，其中约26%接受了住院治疗。

“This data suggests to me that it is reasonable to be cautious about reinfection,” says Theodore Iwashyna, an intensive care unit physician at the VA in Ann Arbor, Mich., who is first author of the preliminary study. 

“在我看来，这些数据表明，我们有理由对再次感染保持警惕。”VA位于密歇根州安娜堡（Ann Arbor）的重症监护室医生西奥多·艾瓦希纳（Theodore Iwashyna）说，他也是这项初步研究的第一作者。

“There’s a lot of reinfection going on in less than 90 days,” says Mark Pandori, director of the Nevada State Public Health Laboratory and an associate professor of pathology at the University of Nevada, Reno. Dr. Pandori and colleagues have documented two cases that were significantly more severe the second time around.

内华达州立公共卫生实验室（Nevada State Public Health Laboratory）主管、内华达大学雷诺分校（University of Nevada, Reno）病理学副教授马克·潘多尼（Mark Pandori）说，“有很多人再次感染时，距离上一次感染都不到90天。”潘多尼博士和同事们已记录了两起第二次感染明显比第一次严重的病例。

Risk of long Covid after reinfection is unclear

再次感染后出现新冠长期后遗症的风险尚不明确

Scientists don’t yet know what the risk of long Covid is after a reinfection. Amesh Adalja, an infectious-disease physician and a senior scholar at Johns Hopkins University Center for Health Security, speculates that you’re less likely to get long Covid after a reinfection–just as vaccines reduce the likelihood of long Covid– because the immune system activates faster the second time around. 

至于再次感染后出现新冠长期后遗症的风险有多高，科学家暂时还不清楚。传染病医生、约翰霍普金斯大学健康安全中心（Johns Hopkins University Center for Health Security）资深学者阿米什·阿达雅（Amesh Adalja）推测，再次感染后，出现新冠长期后遗症的可能性较低——正如疫苗会降低新冠长期后遗症的可能性——因为再次感染时，免疫系统会激活得更快。

“The first infection is the one most likely to lead to complications based on what we know with many other endemic respiratory infectious diseases,” he says. 

“根据我们对其他许多地方性流行性呼吸道传染病的了解，初次感染是最容易引发并发症的。”他说。

But Amy Duckro, an infectious-disease specialist with Kaiser Permanente, says many questions about long Covid remain unanswered. 

不过，凯撒医疗集团（Kaiser Permanente）传染病专家艾米·达克罗（Amy Duckro）指出，许多关于新冠长期后遗症的问题仍没有答案。

“I don’t think we should make any bets on someone who has a reinfection having a less likelihood of having long Covid,” says Dr. Duckro. 

“我觉得我们不应该打赌说，那些再次感染新冠的人出现长期后遗症的可能性更低。”达克罗博士说。

A research group that grew out of the Body Politic patient support group is launching a reinfection study with part of a $3 million grant it recently received to study the impact of reinfections on long Covid patients.

一个从患者扶持机构Body Politic中发展起来的研究组织正利用近日获得的300万美元拨款的一部分，启动一项针对再感染的研究，以此探寻再次感染对新冠长期后遗症患者的影响。

Gina Assaf, a co-founder and co-leader of the research group, says Body Politic has heard from people who got long Covid after a reinfection. “We don’t know to what degree it’s happening, but it is happening,” she says.

该研究组织联合创始人兼领导者之一吉娜·阿萨夫（Gina Assaf）说，Body Politic曾听说有人再次感染新冠后出现了长期后遗症。她说，“我们不知道这种情况有多普遍，但它的确存在。”