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.

中國呼吸道病毒感染病例激增的報導讓人想起五年前新冠疫情暴發時的慘痛經歷。

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

但醫學專家表示，儘管表面上有相似之處，但這次的情況截然不同，而且遠沒有那麼令人擔憂。

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

據報導，中國病例感染的是人偏肺病毒，醫生稱之為HMPV。以下是我們目前所了解的情況：

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傳播的幾種病原體之一，可引發呼吸道疾病。HMPV很常見——非常常見，以至於大多數人在兒童時期就會被感染，並且一生中可能會經歷多次感染。在天氣寒冷持續數月的國家，HMPV可能每年都有一個傳播季，就像流感一樣，而在赤道附近的地方，該病毒全年都在以較低水平傳播。

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與在美國更為人熟知的一種病毒——呼吸道合胞病毒(RSV)相似。它引發的癥狀與流感和新冠非常像，包括咳嗽、發燒、鼻塞和氣喘。

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.

大多數HMPV感染癥狀較輕，類似於普通感冒。但嚴重病例可能導致支氣管炎或肺炎，尤其是在嬰兒、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氣腫等肺部疾病的患者出現嚴重後果的風險更高。

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

在高收入國家，這種病毒很少致命；在衛生系統薄弱、監測不力的低收入國家，死亡情況更為常見。

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.

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，除非有人因確診感染該病毒而住院，否則很少會提到它的名字。

“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.”

「其臨床特徵確實很難與其他病毒性疾病區分開來，而且我們不會像檢測新冠、流感或呼吸道合胞病毒那樣定期檢測HMPV，」霍華德博士說，「因此，大多數感染都未被發現，並被算作其他正在流行的呼吸道疾病。」

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.

該病毒主要通過咳嗽或打噴嚏時產生的飛沫或氣溶膠傳播，也能通過與感染者的直接接觸或接觸受污染的表面傳播——基本上與人們感染感冒、流感和新冠的方式相同。

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.

目前尚無針對HMPV的疫苗。但有針對RSV的疫苗，且目前正在研究一種疫苗，只需注射一次即可預防這兩種病毒，因為它們很相似。目前尚無專門針對HMPV的抗病毒治療方法；治療側重於控制癥狀。

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.

中國當局承認HMPV病例正在增加，但強調該病毒是一種已知病毒，並不是什麼大問題。導致新冠的冠狀病毒在當時是一種新病原體，因此人們的免疫系統尚未對其建立防禦能力。

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.

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.

他說，在1月底的農曆新年假期期間，由於許多人出行和聚集，病例可能會增加。

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.”

但闞飆表示，總體來說，「從目前情況看，今年呼吸道傳染病的流行規模和強度比去年要低一些。」

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.

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.”

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.

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.

網路上，有人評論說他們從未聽說過HMPV，並擔心這是一種新的病原體，對此，官方媒體試圖安撫民眾，提醒他們不要盲目服用抗病毒藥物。

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.

一些網友開玩笑說，他們終於可以用完在新冠疫情期間囤積的口罩了。許多網友討論了疾病發病率普遍上升的問題，而不僅僅是HMPV：「為什麼感染甲流這麼疼啊」週一在微博上成為熱門話題。

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.

世衛組織尚未表達擔憂。該組織發言人瑪格麗特·哈利斯博士援引中國當局的每週報告稱，病例數量正在可預見地上升。

“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.

「正如預期的那樣，每年這個時候，也就是北半球的冬季，急性呼吸道感染病例數都會逐月增加，包括季節性流感、呼吸道合胞病毒和人偏肺病毒，」她在電子郵件中表示。

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.”

週二，世衛組織發表聲明稱：「世衛組織正與中國衛生官員保持聯繫，尚未收到任何有關病例暴發異常模式的報告。」聲明還說：「中國當局報告稱，醫保系統並未不堪重負，也沒有發布緊急聲明或觸發應對措施。」

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.

來自中國的報告讓人想起新冠疫情暴發初期那些令人困惑的日子。五年過去了，世衛組織仍在敦促中國分享更多有關疫情起源的信息。

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.

但目前的情況在一些重要方面有所不同。新冠病毒是一種從動物傳播到人類的病毒，此前未知。HMPV已得到充分研究，並且有廣泛的檢測能力。全球範圍內對這種病毒具有廣泛的群體免疫；而新冠病毒是沒有的。嚴重的HMPV感染季可能會給醫院承載帶來壓力——尤其是兒科病房——但不會讓醫療機構不堪重負。

“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，中國及時分享有關此次病例暴發的數據也至關重要，」傳染病專家、澳洲國立大學醫學副教授桑賈亞·塞納那亞克博士說。「這包括有關感染者的流行病學數據。此外，我們還需要基因組數據來確認HMPV是感染元兇，且沒有任何值得關注的重大突變。」