Recently the New York Times reported the following:
Scientists Get a Glimpse of How New Pandemics Are Made
(1/2)
Researchers have devised a new tool for discerning
between naturally occurring viral outbreaks and those resulting from lab
accidents.
The NYT - By Carl Zimmer
March 9, 2026
Updated 9:43 a.m. ET
The Covid pandemic was an extraordinary moment in history.
Starting at the end of 2019, a virus new to science swept across the planet,
killed more than 25 million people and caused trillion of dollars in economic
damage.
But as outbreaks go, Covid was pretty ordinary, a new study finds.
Scientists compared seven viral outbreaks that occurred in recent decades, including epidemics of Covid, Ebola and influenza. For the most part, the researchers found, the outbreaks were not preceded by any unusual genetic changes in the viruses. In all but one case, in 1977, the viruses circulated in animals and gained the ability to spread to and among people only by unfortunate coincidence.
“We see that time and again,” said Joel Wertheim, a virologist at the University of California San Diego. He and his colleagues published the study on Friday in the journal Cell.
Dr. Wertheim and his colleagues reconstructed the evolutionary history of these viruses by looking at their genes. They tracked how viruses gained different kinds of mutations before causing outbreaks and looked at that pattern after the viruses jumped into the human population.
In one line of research, the scientists examined the influenza pandemic of 2009. In that year, a new strain of influenza emerged in North America and went on to infect one-quarter of all people on Earth and kill 230,000.
Other studies of the virus have revealed that it came from pigs, where influenza viruses gain mutations on a regular basis. Some mutations made it harder for the viruses to spread to other pigs. Others provided an evolutionary edge; still others had no effect.
The viral strain that jumped into humans in 2009 had split off as its own evolutionary branch at least a decade earlier. Until it reached humans, its evolution looked ordinary; the pattern of mutations gained and lost by the virus resembled what scientists would expect to see in any flu virus thriving in pigs.
Only after the virus jumped to humans did things change, and dramatically.
After infecting humans in 2009, the flu virus gained many new mutations. In pigs, those mutations would probably have hindered the virus’s ability to multiply and caused it to be outcompeted by other viruses infecting the animals.
But once the virus settled in a new host, those old constraints were gone. It began adapting to spread more successfully in humans.
Dr. Wertheim and his colleagues ran the same analysis on other outbreaks, including the Ebola epidemic that swept across West Africa in 2013 and is thought to have originated in a bat, and the 2022 outbreak of mpox, a virus that causes painful blisters and is believed to be harbored by African squirrels. Again and again, the researchers saw the same pattern: The viruses that eventually jumped into humans did not evolve in an unusual way beforehand but did change dramatically afterward.
“Once it gets into humans, it’s a new day,” Dr. Wertheim said.
But one virus turned out to be a major exception to that rule, the new study found. Its unique mutations suggest that it may have been set loose by a scientific accident.
In 1977, the world was hit by a pandemic that came to be known as Russian flu, because the first cases were reported by the Soviet Union. Scientists were baffled by the virus: Its closest relatives were not in pigs or other animals but instead looked a lot like viruses that were circulating in the early 1950s, a quarter-century earlier.
Some scientists speculated that the Russian flu was not a spillover from a pig or a bird. Rather, they suggested, it had emerged from a scientific mishap, perhaps a vaccine trial that had gone wrong in the Soviet Union or China.
The vaccine makers might have used a common technique that involved producing a vaccine made of weakened viruses. Viruses growing in Petri dishes in a lab accumulate mutations that would harm them if they were infecting a person. Scientists speculated that Soviet or Chinese scientists thawed out some old flu virus to make a weakened vaccine but used faulty techniques that allowed the virus to spread from person to person.
(to be continued)
Translation
科學家窺見新疫情的起源（1/2）
研究人員開發出一種新工具，用於區分由自然發生的病毒爆發疫情和由實驗室事故導致的爆發
新冠疫情是歷史上一個非同尋常的時刻。從2019年底開始，一種科學界先前未知的病毒席捲全球，造成超過2,500萬人死亡，並造成數兆美元的經濟損失。
但一項新的研究發現，就疫情爆發而言，新冠疫情其實相當普通。
科學家比較了近幾十年來發生的七次病毒爆發，包括新冠疫情、伊波拉疫情和流感疫情。研究人員發現，在大多數情況下，這些疫情爆發之前病毒並沒有發生任何異常的基因變化。除了1977年的那次例外，所有病毒都是在動物中傳播，並因不幸的巧合而獲得了在人與人之間傳播的能力。
加州大學聖地牙哥分校的病毒學家Joel Wertheim說:「我們一次又一次地看到這種情況」。他和他的同事於週五在《細胞》（Cell）雜誌上發表了這項研究。
Wertheim博士和他的同事透過分析病毒的基因，重建了這些病毒的演化史。他們追蹤了病毒在引發疫情之前如何獲得不同類型的突變，並研究了病毒進入人類群體後這種突變模式的變化。
在其中一項研究中，科學家檢視了2009年的流感大流行。那一年，一種新的流感病毒株在北美出現，並感染了全球四分之一的人口，造成23萬人死亡。
其他針對病毒的研究表明它來自豬，而流感病毒在豬體內經常發生突變。有些突變使病毒更難傳播給其他豬。有些突變則賦予了病毒進化優勢；有些突變則沒有產生任何影響。
2009年感染人類的病毒株至少在十年前就已經分化成一個獨立的演化分支。在感染人類之前，它的進化過程看起來很普通；病毒獲得的突變和缺失的模式與科學家預期在豬群中傳播的任何流感病毒的模式相似。
只有在病毒感染人類之後，情況才發生了劇烈的變化。
流感病毒在2009年感染人類後，獲得了許多新的突變。在豬群中，這些突變可能會阻礙病毒的繁殖能力，並使其在去感染其他動物的病毒競爭中敗下陣來。
但是，一旦病毒在新宿主中定居下來，這些原有的限制就消失了。它開始適應環境，從而更容易在人類中傳播。
Wertheim博士及其同事對其他疫情進行了同樣的分析，包括2013年席捲西非的伊波拉疫情（相信起源於蝙蝠）以及2022年的麻疹病毒疫情（一種會導致疼痛水皰的病毒，相信由非洲松鼠攜帶）。研究人員一次又一次地觀察到相同的模式：最終傳播到人類的病毒在傳播前並沒有異常的演化，但在傳播後卻發生了顯著的變化。
Wertheim博士說: 「一旦病毒進入人類體內，那就是嶄新的一天」。
但新的研究發現，有一種病毒是這個規則的主要例外。其獨特的突變表明，它可能是由科學事故釋放出來的。
1977年，一場被稱為「俄羅斯流感」的全球性流行病席捲全球，因為首批病例是由蘇聯報告的。科學家對這種病毒感到困惑：它的近親並非來自豬或其他動物，而是與25年前，也就是20世紀50年代初期流行的病毒非常相似。
一些科學家推測，俄羅斯流感並非源自豬或禽類。他們認為，它可能是科學事故的產物，例如蘇聯或中國疫苗試驗中出現的失誤。
疫苗生產商可能採用了一種常見的技術，即用減弱病毒去製造疫苗。在實驗室培養皿中培養的病毒會累積突變，如果它感染人類，這些變異會對病毒造成傷害。科學家推測，蘇聯或中國的科學家解凍了某種舊的流感病毒來製造減弱病毒疫苗，但由於使用了錯誤的技術，導致病毒在人與人之間傳播。
（待續）
