Reports of a surge in cases of a respiratory virus in China have evoked dark echoes of the start of the Covid-19 pandemic almost exactly five years ago.

中国呼吸道病毒感染病例激增的报道让人想起五年前新冠疫情暴发时的惨痛经历。

But despite the surface similarities, this situation is very different, and far less worrisome, medical experts say.

但医学专家表示，尽管表面上有相似之处，但这次的情况截然不同，而且远没有那么令人担忧。

The Chinese cases are reported to be infections with human metapneumovirus, known to doctors as HMPV. Here is what we know so far:

据报道，中国病例感染的是人偏肺病毒，医生称之为HMPV。以下是我们目前所了解的情况：

What is HMPV?

什么是HMPV?

It is one of several pathogens that circulate across the world each year, causing respiratory illnesses. HMPV is common — so common that most people will be infected while they are still children and may experience several infections in their lifetimes. In countries with months of cold weather HMPV can have an annual season, much like the flu, while in places closer to the Equator it circulates at lower levels all year long.

它是每年在世界各地传播的几种病原体之一，可引发呼吸道疾病。HMPV很常见——非常常见，以至于大多数人在儿童时期就会被感染，并且一生中可能会经历多次感染。在天气寒冷持续数月的国家，HMPV可能每年都有一个传播季，就像流感一样，而在赤道附近的地方，该病毒全年都在以较低水平传播。

HMPV is similar to a virus that is better known in the United States — respiratory syncytial virus, or R.S.V. It causes symptoms much like those associated with flu and Covid, including cough, fever, nasal congestion and wheezing.

HMPV与在美国更为人熟知的一种病毒——呼吸道合胞病毒(RSV)相似。它引发的症状与流感和新冠非常像，包括咳嗽、发烧、鼻塞和气喘。

Most HMPV infections are mild, resembling bouts of the common cold. But severe cases can result in bronchitis or pneumonia, particularly among infants, older adults and immunocompromised people. Patients with pre-existing lung conditions, such as asthma, chronic obstructive pulmonary disease or emphysema, are at higher risk of severe outcomes.

大多数HMPV感染症状较轻，类似于普通感冒。但严重病例可能导致支气管炎或肺炎，尤其是在婴儿、老年人和免疫功能低下的人群中。患有哮喘、慢性阻塞性肺病或肺气肿等肺部疾病的患者出现严重后果的风险更高。

In higher-income countries, the virus is rarely fatal; in lower-income countries, with weak health systems and poor surveillance, deaths are more common.

在高收入国家，这种病毒很少致命；在卫生系统薄弱、监测不力的低收入国家，死亡情况更为常见。

How long has this virus been around?

这种病毒已经存在多久了？

The virus was identified in 2001, but researchers say it has circulated in humans for at least 60 years. Though it is not new, it doesn’t have the name recognition of influenza, Covid or even R.S.V., said Dr. Leigh Howard, an associate professor of pediatric infectious disease at Vanderbilt University Medical Center.

该病毒于2001年被发现，但研究人员表示，它已在人类中传播了至少60年。范德堡大学医学中心儿科传染病副教授利·霍华德博士说，虽然不是新病毒，但它的知名度不如流感、新冠病毒甚至呼吸道合胞病毒。

One reason is that it is rarely discussed by name, except when people are hospitalized with a confirmed case of it.

原因之一是，除非有人因确诊感染该病毒而住院，否则很少会提到它的名字。

“The clinical features are really difficult to distinguish from other viral illnesses, and we don’t routinely test for HMPV the way we do for Covid, flu or R.S.V.,” Dr. Howard said. “So most infections go unrecognized and are chalked up to whatever respiratory thing is going around.”

“其临床特征确实很难与其他病毒性疾病区分开来，而且我们不会像检测新冠、流感或呼吸道合胞病毒那样定期检测HMPV，”霍华德博士说，“因此，大多数感染都未被发现，并被算作其他正在流行的呼吸道疾病。”

How does a person get infected with HMPV?

人是如何感染HMPV的？

The virus spreads primarily through droplets or aerosols from coughing or sneezing, through direct contact with an infected individual or through exposure to contaminated surfaces — basically the same ways people get colds, flu and Covid.

该病毒主要通过咳嗽或打喷嚏时产生的飞沫或气溶胶传播，也能通过与感染者的直接接触或接触受污染的表面传播——基本上与人们感染感冒、流感和新冠的方式相同。

Is there a vaccine? Or a treatment?

有疫苗或治疗方法吗？

There is no vaccine against HMPV. But there is a vaccine for R.S.V., and research is underway to find a vaccination that could protect against both viruses with one shot, since they are similar. There is no antiviral treatment specifically for HMPV; treatment focuses on management of symptoms.

目前尚无针对HMPV的疫苗。但有针对RSV的疫苗，且目前正在研究一种疫苗，只需注射一次即可预防这两种病毒，因为它们很相似。目前尚无专门针对HMPV的抗病毒治疗方法；治疗侧重于控制症状。

What is China saying about it?

中国对此有何表态？

The Chinese authorities have acknowledged that HMPV cases are increasing, but have emphasized that the virus is a known entity and is not a major concern. The coronavirus that causes Covid-19 was a new pathogen, so people’s immune systems had not built up defenses against it.

中国当局承认HMPV病例正在增加，但强调该病毒是一种已知病毒，并不是什么大问题。导致新冠的冠状病毒在当时是一种新病原体，因此人们的免疫系统尚未对其建立防御能力。

At a news conference held by China’s Center for Disease Control and Prevention on Dec. 27, Kan Biao, the director of the center’s Institute for Infectious Diseases, said that HMPV cases were rising among children 14 years and younger. The increase was especially notable in northern China, he said. Influenza cases have also increased, he said.

12月27日，中国疾控中心传染病所所长阚飙在新闻发布会上表示，14岁以下儿童中HMPV病例呈上升趋势。他说，这种增长在中国北方尤为明显，并表示流感病例也有所增加。

Cases could spike during the Lunar New Year holiday, at the end of January, when many people travel and gather in large groups, he said.

他说，在1月底的农历新年假期期间，由于许多人出行和聚集，病例可能会增加。

But overall, Mr. Kan said, “judging from the current situation, the scale and intensity of the spread of respiratory infectious diseases this year will be lower than last year’s.”

但阚飙表示，总体来说，“从目前情况看，今年呼吸道传染病的流行规模和强度比去年要低一些。”

Official Chinese data shows that HMPV cases have been rising since mid-December, in both outpatient and emergency cases, according to Xinhua, the state news agency. Some parents and social media users were unfamiliar with the virus and were seeking advice online, the outlet said; it urged calm and ordinary precautions such as washing one’s hands frequently and avoiding crowded places.

据中国国家通讯社新华社报道，中国官方数据显示，自12月中旬以来，门诊和急诊中HMPV病例一直在增加。该媒体称，一些家长和社交媒体用户对这种病毒不熟悉，在网上寻求建议；文章敦促人们保持冷静，采取日常预防措施，例如勤洗手，以及避免去人多拥挤的地方。

In a routine media briefing on Friday, a spokesperson for the Foreign Ministry reiterated that cases of influenza and other respiratory viruses routinely increase at this time of year but that they “appear to be less severe and spread on a smaller scale compared with the previous year.”

在周五的例行新闻发布会上，外交部发言人重申，每年这个时候流感和其他呼吸道病毒病例都会增加，但“目前看，相关疾病的流行规模和强度比去年要低一些”。

Chinese officials said last week that it would set up a monitoring system for pneumonia of unknown origin. It will include procedures for laboratories to report cases and for disease control and prevention agencies to verify and handle them, the state broadcaster CCTV reported.

中国官员上周表示，将建立不明原因肺炎监测系统。据国家电视台中央电视台报道，该系统将包括实验室报告病例的程序，以及疾控机构核实处置的流程。

What has the public response in China been?

中国公众的反应如何？

Online, amid comments from people saying they had never heard of HMPV and expressing concern that it was a new pathogen, state media outlets have sought to reassure people, warning them against blindly taking antiviral medications.

网络上，有人评论说他们从未听说过HMPV，并担心这是一种新的病原体，对此，官方媒体试图安抚民众，提醒他们不要盲目服用抗病毒药物。

Some users have cracked jokes, saying that they could finally use up the masks they had stockpiled during the coronavirus pandemic. Many commenters have discussed a general uptick in illness, not just HMPV: “Why does the flu hurt so much” was trending on Weibo, a social media platform, on Monday.

一些网友开玩笑说，他们终于可以用完在新冠疫情期间囤积的口罩了。许多网友讨论了疾病发病率普遍上升的问题，而不仅仅是HMPV：“为什么感染甲流这么疼啊”周一在微博上成为热门话题。

What does the World Health Organization say?

世界卫生组织怎么说？

The W.H.O. has not expressed concern. Dr. Margaret Harris, a spokeswoman for the organization, cited weekly reports from the Chinese authorities that showed a predictable rise in cases.

世卫组织尚未表达担忧。该组织发言人玛格丽特·哈里斯博士援引中国当局的每周报告称，病例数量正在可预见地上升。

“As expected for this time of year, the Northern Hemisphere winter, there is a month-over-month increase of acute respiratory infections, including seasonal influenza, R.S.V. and human metapneumovirus,” she said by email.

“正如预期的那样，每年这个时候，也就是北半球的冬季，急性呼吸道感染病例数都会逐月增加，包括季节性流感、呼吸道合胞病毒和人偏肺病毒，”她在电子邮件中表示。

On Tuesday, the organization put out a statement saying, “W.H.O. is in contact with Chinese health officials and has not received any reports of unusual outbreak patterns.” It added, “Chinese authorities report that the health care system is not overwhelmed and there have been no emergency declarations or responses triggered.”

周二，世卫组织发表声明称：“世卫组织正与中国卫生官员保持联系，尚未收到任何有关病例暴发异常模式的报告。”声明还说：“中国当局报告称，医保系统并未不堪重负，也没有发布紧急声明或触发应对措施。”

Should I worry?

我应该担心吗？

The reports coming from China are evocative of those from the first, confusing days of the Covid pandemic, and the W.H.O. is still urging China to share more information about the origin of that outbreak, five years on.

来自中国的报告让人想起新冠疫情暴发初期那些令人困惑的日子。五年过去了，世卫组织仍在敦促中国分享更多有关疫情起源的信息。

But the current situation is different in key respects. Covid was a virus that spilled over into humans from animals and was previously unknown. HMPV is well studied, and there is widespread capacity to test for it. There is broad population-level immunity to this virus globally; there was none, for Covid. A severe HMPV season can strain hospital capacity — particularly pediatric wards — but does not overwhelm medical centers.

但目前的情况在一些重要方面有所不同。新冠病毒是一种从动物传播到人类的病毒，此前未知。HMPV已得到充分研究，并且有广泛的检测能力。全球范围内对这种病毒具有广泛的群体免疫；而新冠病毒是没有的。严重的HMPV感染季可能会给医院承载带来压力——尤其是儿科病房——但不会让医疗机构不堪重负。

“However, it is also vital for China to share its data on this outbreak in a timely manner,” said Dr. Sanjaya Senanayake, a specialist in infectious diseases and associate professor of medicine at the Australian National University. “This includes epidemiologic data about who is getting infected. Also, we will need genomic data confirming that HMPV is the culprit, and that there aren’t any significant mutations of concern.”

“然而，中国及时分享有关此次病例暴发的数据也至关重要，”传染病专家、澳大利亚国立大学医学副教授桑贾亚·塞纳那亚克博士说。“这包括有关感染者的流行病学数据。此外，我们还需要基因组数据来确认HMPV是感染元凶，且没有任何值得关注的重大突变。”