想要預防大流行？停止溢出事件
決策者討論有關健康和生物多樣性的里程碑式協議時必須包含四項行動，以降低動物和人類交換病毒的風險。
資料來源：Nature 605, 419-422 (2022) ；財團法人台灣紅絲帶基金會編譯
當樹木被燒毀以清理土地供放牧時，牛群侵占了巴西的亞馬遜熱帶雨林。圖：Bruno Kelly/Reuters/Alamy
–
源自於動物的病原體跳到人體的溢出事件可能引發了自 20 世紀初以來發生的每一次病毒大流行。更重要的是，2021 年 8 月對過去四個世紀疾病爆發的分析顯示，未來幾十年大流行的年度概率可能會增加幾倍，這主要是由於人類所引起的環境變化。
幸運的是，大約每年200 億美元的資金，可使溢出的可能性大大地降低。這是將全球新興傳染病熱點地區的森林砍伐減半；大幅減少和規範野生動物貿易；大大提升養殖動物傳染病的檢測和控制能力等所需的金額。
與在 COVID-19 大流行中所失去的數百萬人的生命和花費的數兆之美元相比，這是一筆很小的投資。其成本也是自 1918 年以來每年從動物身上溢出的病毒性疾病所造成的生命損失統計值的二十分之一，並且是每年經濟生產力被抹去之不到十分之一的金額。
–
–
溢出事件：一項成長中的威脅
森林砍伐和其他的改變己經增加動物病毒跳躍至人身上。隨著全球化及人口的更加密集所逐漸增加這些溢出事件將會是災難性的。自1918年以來因病毒性人畜共通傳染病每年的經濟損失為2120億美元。
數據來自人畜共通來源之病毒性群突發事件導致十個或更多的死亡，括號中的數字是跨越多年之總估計死亡數（以及在某些事件，係跨越多個群突發）捨入後最接近於十
資料來源：參考文獻 1
然而，在 COVID-19 大流行的推動下，許多旨在更好地保護世界免受未來疫情爆發的國際努力仍然未能優先考慮到防止溢出。以世界衛生組織 (WHO) 設立的大流行防範和應對獨立小組為例。該小組於 2020 年 9 月召開，部分原因是為了確保未來的任何傳染病爆發都不會成為另一場大流行。在去年 5 月發布的 86 頁報告中，只有兩次提到了野生動物，森林砍伐只有一次。
我們敦促目前正在制定三項具有里程碑意義的國際努力的決策者將防止溢出效應作為每一項行動的核心。
首先，由全球 20 個最大經濟體組成的 G20 集團上個月臨時同意設立一個全球大流行基金。如果實現，這可以提供傳染病專家幾十年來一直推薦的資金水平——全球每人每年約 5 美元。其次，世界衛生組織的決策機構世界衛生大會（WHA）正在討論一項改進全球大流行應對方法的協議。第三，生物多樣性公約締約方正在談判生物多樣性保護框架草案——2020年後全球生物多樣性框架。
以正確的方式設計，這三項國際努力可以促進對傳染病採取更積極主動的全球方法。這個機會——最終解決導致重大疾病爆發的因素，其中許多也導致氣候變遷和生物多樣性的喪失——可能不會再次出現，直到世界面臨另一場大流行。
–
–
四個動作
當動物和人類有更多接觸的機會時，溢出的風險就更大，例如在野生動物貿易、畜牧業或森林被砍伐以進行採礦、耕作或道路時。在增加受感染動物傳播病毒的可能性條件下，也更有可能發生這種情況——例如，當它們被安置在狹窄的環境中或餵養不當時。
流行病學、生態學和遺傳學數十年的研究顯示，降低溢出風險的有效全球戰略應側重於四項行動。
–
首先，必須保護熱帶和亞熱帶森林。各種研究顯示，土地使用方式的改變，特別是熱帶和亞熱帶森林，可能是全球新興的人畜共通傳染病的最大驅動因素。在森林砍伐或退化中倖存下來的野生動物往往包括可以與人類共同生活的物種，並且通常攜帶能夠感染人類的病原體。例如，在孟加拉國，攜帶立百病毒的蝙蝠——它可以殺死 40-75% 的感染者——現在棲息在人口密度高的地區，因為它們的森林棲息地幾乎已被完全清除。
此外，森林的喪失正在推動氣候變遷。這本身可以透過將蝙蝠等動物趕出已變荒涼的地區並進入許多人居住的地區來有助於溢出。
然而，只要有足夠的政治意願和資源，即使在農業生產力提高時，森林也可以得到保護。 2004-12 年間亞馬遜地區森林砍伐減少 70% 證明了這一點，主要是通過更好的監測、執法和向農民提供經濟激勵措施。 （由於環境立法的變化，森林砍伐率在 2013 年開始增加，並且自 2019 年賈爾·博爾索納羅（Jair Bolsonaro）擔任總統期間急劇上升。）
–
其次，必須在國內和國際上禁止或嚴格監管構成公共衛生風險的活體野生動物的商業市場和貿易。
這樣做符合世界衛生組織和其他組織在 2021 年發出的呼籲，即各國暫時停止活捕野生哺乳動物的貿易，並關閉市場中出售此類動物的部門。一些國家已經按照這些路線採取了行動。在中國，針對 COVID-19，大多數陸生野生動物的貿易和消費已被禁止。同樣，加蓬也禁止在市場上出售某些哺乳動物作為食物。
中國安徽省一個擁擠的養雞場的工人。圖片來源：Jianan Yu/Reuters
對城市和城郊商業市場和貿易的限制不得侵犯原住民族和當地社區的權利和需求，他們經常依賴野生動物來保障糧食安全、生計和文化習俗。在包括巴西、加拿大和美國在內的許多國家，根據社區的不同，已經有不同的狩獵規則。
–
第三，在處理養殖動物時必須提高生物安全性。除其他措施外，這可以透過更好的獸醫照顧、加強對動物疾病的監測、改善飼養和圈養動物，以及隔離以限制病原體的傳播來實現。
養殖動物的健康狀況不佳會增加它們感染病原體以及傳播病原體的風險；近 80% 的牲畜病原體可以感染多種宿主物種，包括野生動物和人類。
–
第四是特別是在傳染病多發之熱點地區，要提高民眾的健康和經濟安全。
健康狀況不佳的人——例如營養不良或愛滋病毒感染不受控制的人——可能更容易感染人畜共通疾病之病原體。而且，特別是在像這樣的免疫抑制個體中，病原體在傳染給其他人之前可能會發生變異。
此外，一些社區——尤其是農村地區的社區——利用自然資源生產商品或創造收入，從而使他們接觸到野生動物或野生動物副產品。例如，在孟加拉國，椰棗樹汁以各種形式作為飲料飲用，通常收集於附在棕櫚樹上的盆子中。這些設施可能會被蝙蝠的身體物質污染。 2016 年的一項調查認為這種做法與14 起人類立百病毒感染並導致 8 人死亡事件有關聯。
為社區提供教育和工具以降低傷害風險至關重要。在孟加拉國的例子中，可以像盆蓋一樣簡單之工具，便足以防止椰棗樹汁受到污染。
事實上，提供教育機會以及醫療保健服務和替代生計技能之培訓，如有機農業，可以幫助人類和環境。例如，俄勒岡州波特蘭市的非政府組織 Health in Harmony 已投資於印度尼西亞婆羅洲的社區設計之介入措施。在 2007-17 年間，這些措施減少了 90%以非法採伐為主要生計的家庭數量。這又反過來將當地雨林的損失減少了 70%。該計畫服務區的嬰兒死亡率也下降了 67%。
這種以系統為導向的介入措施需要更好地被理解，並將最有效的介入措施予以擴增。
–
–
明智的投資
這種防止溢出的策略將減少我們對遏制措施的依賴，例如人類疾病監測、接觸者追踪、封鎖、疫苗和治療。這些介入措施至關重要，但往往成本高昂且實施得太晚——簡而言之，單獨使用它們不足以應對新興的傳染病。
COVID-19 大流行暴露了這些反應措施在現實世界中的局限性——尤其是在虛假信息和民粹主義抬頭的時代。例如，儘管截至 3 月底，美國聯邦政府在應對大流行病方面花費了超過 3.7 兆美元，但美國仍有近 100 萬人（即大約每 330 人中的一人）死於 COVID-19。在全球範圍內，估計在 COVID-19 大流行期間失去了 1500 萬至 2100 萬人的生命，超出了在非大流行條件下的預期人數（稱為超額死亡）。 2021 年的模型顯示，到 2025 年，僅 COVID-19 疫苗就將花費 1570 億美元。
緬甸的一位農民從棕櫚樹上採集汁液來釀酒。被蝙蝠排泄物污染的收集罐中汁液可將疾病傳播給人類。
圖片來源：Wolfgang Kaehler/LightRocket via Getty
防止溢出還可以保護那些地方的人、馴養動物和野生動物承受最小的傷害——使其比採取遏制更公平。例如，自從 COVID-19 疫苗首次公開獲得的近 18 個月以來，非洲總人口中只有 21% 至少接種過一劑疫苗。而在美國和加拿大，這一數字接近 80%。與此同時，輝瑞的藥品總銷售額從 2020 年的 430 億美元增長到 2021 年的 720 億美元，這主要歸功於該公司的 COVID-19 疫苗，這是 2021年最暢銷的藥物。
最後，與遏制措施不同，防止外溢的行動也有助於阻止外溢，即人畜共通疾病之病原體從人類身上轉移到動物身上，然後再次進入人體。不同物種的選擇壓力可能不同，讓這種跳躍成為逃避現有免疫的新變異株之可能潛在來源。一些研究人員認為，溢出可能是 SARS-CoV-2 的 Omicron 變異株出現的原因。
–
–
把握光陰
過去一年，美國總統喬·拜登（Joe Biden）的政府和兩個國際小組（一個由世界衛生組織於 2020 年成立，另一個由 G20 於 2021 年成立）發布了有關如何改進應對大流行方法的指南。迄今為止發布的所有建議都承認溢出是新興傳染病的主要原因。卻沒有人充分討論如何減輕這種風險。同樣，在 PubMed 中搜索 SARS-CoV-2 的刺突蛋白產生了數千篇論文，但只有少數研究調查了蝙蝠體內的冠狀病毒動力學，而 SARS-CoV-2 很可能來自蝙蝠。
出於幾個原因，溢出的預防可能會被忽視。病原體的上游動物和環境來源可能被生物醫學研究人員及其資助者所忽略，因為它們是複雜系統中的一部分——研究往往不會帶來有形的、有利可圖的產出。此外，大多數從事公共衛生和生物醫學科學工作的人在生態學、野生動物生物學、保護和人類學方面的訓練很有限。
氣候變遷將促使動物之間產生新的邂逅相遇——並促進病毒性疾病爆發
人們越來越認識到跨部門合作的重要性，包括大力倡導「健康一體」的方法——一種認知到環境、動物和人類之間關聯的整合健康觀。但是，總的來說，這還沒有轉化為預防大流行的行動。
另一個挑戰是，可能需要幾十年才能實現防止溢出的好處，而不是幾週或幾個月的遏制措施。無論經過多長時間，溢出預防的效益都難予以量化，因為如果措施成功，就不會發生爆發流行。預防也與個人、社會和政治上均傾向於等待災難再採取行動的趨勢背道而馳。
全球大流行基金、世界衛生大會大流行協議和 2020 年後全球生物多樣性框架都提供了轉變這種思維方式的新機會，並同時於開展關鍵性的大流行防範工作時，處於協調一致的全球努力上以降低溢出的風險。
–
–
全球大流行基金
首先且最重要的，全球大流行基金將是確保將預防溢出的大量證據轉化為行動的關鍵。防止溢出的資金不應併入現有的保護基金，也不應動用任何其他現有的資金流。
投資必須針對溢出風險最大的地區和行為，從東南亞和中非到亞馬遜盆地及其他地區。防止這些地區溢出的行動，特別是透過減少森林砍伐，也將有助於緩解氣候變遷和減少生物多樣性的喪失。但保護本身的資金嚴重不足。例如，自然解決方案（例如森林、濕地和草原的保護、恢復和管理的改進）占將氣候變暖於2030 年穩定在遠低於 2°C所需的氣候緩解措施的三分之一以上。然而，這些方法獲得的全球氣候減緩資金卻不到 2%。 （能源系統收到一半以上。）
簡而言之，支持全球大流行基金的決策者絕不能假設現有基金正在應對溢出的威脅——事實並非如此。儘管 COVID-19 引發了經濟衰退，但 2020 年原始熱帶森林的損失比 2019 年高 12%。這凸顯了對森林的持續威脅。
資金必須持續數十年，以確保降低溢出風險的努力持續足夠長的時間以產生成果。
–
–
世界衛生大會大流行協議
2020 年，歐洲理事會主席查爾斯·米歇爾（Charles Michel）呼籲制定一項條約，以使全球對重大流行病和大流行的反應更加協調。去年，20 多位世界領導人開始響應這一呼籲，世界衛生大會在 2021 年底啟動了一項協議（可能是條約或其他國際文書）的談判，以「加強大流行的預防、準備和應對」。
這樣一項多邊協議有助於確保圍繞在轉讓科學知識、醫療用品、疫苗和療法上，採取更加公平的國際行動。它還可以解決目前對世衛組織施加的一些限制，並更清楚地定義各國政府必須將潛在的疾病威脅通知其他人的條件。 COVID-19 的大流行暴露了《國際衛生條例》在許多這些前線上的缺陷。（該法律框架定義了各國在處理可能跨越國界的公共衛生事件和緊急情況時的權利和義務。）
健康一體的方法需要社區參與、教育和國際合作——盧旺達的一個教訓
我們敦促談判者確保此處所列舉的防止溢出的四項行動在 WHA 大流行協議中得到優先考慮。例如，它可能要求各國為大流行制定國家行動計畫時，包括減少森林砍伐和關閉或嚴格監管活體野生動物市場。還應建立一個報告機制來評估協議的執行進展情況。這可以借鑑現有計畫的經驗，例如世衛組織聯合外部評估程序（Who Joint External Evaluation process，用於評估各國處理公共衛生風險的能力）和《化學武器公約》的核查制度。
在人類、馴養動物和野生動物接口之間擴大病原體監測的承諾——從美國的水貂養殖場和亞洲的濕貨市場到南美洲的森林砍伐嚴重的地區——也應納入世界衛生大會協議。監測並不會防止溢出，但它可以更早地發現和更好地控制人畜共通疾病暴發，並更好地了解導致它們的條件。只需對新興傳染病熱點地區的人和動物的臨床照護進行投資，疾病監測就會得到改善。
–
–
生物多樣性公約
我們正處於第六次大滅絕之中，導致生物多樣性喪失的活動，例如森林砍伐，也助長了傳染病的出現。同時，對自然的開發結果所引起的流行病和大流行能導致更進一步保護的受挫——在許多因素中，例如因旅遊業喪失所造成的經濟損失和人員的短缺影響保護區的管理等。此外，感染人類的病原體亦可能會傳播給其他動物並導致這些種群大量減少。例如， 2002-03 年剛果共和國爆發的伊波拉病毒被認為已導致 5,000 隻大猩猩死亡。
然而，目前正在談判的全球生物多樣性框架《生物多樣性公約》未能明確解決環境退化、野生動物開發和病原體出現之間的負反饋循環。初稿並沒有提到全球大流行。 3 月份提出了關於防止溢出的文本，但尚未達成一致。
同樣，這種遺漏主要源自於學科和專業知識的孤立。正如世界衛生大會大流行協議所依賴的專家往往是衛生部門的專家一樣，為《生物多樣性公約》提供信息的專家往往是環境科學和保護方面的專家。
計畫於今年晚些時候在締約方大會上商定的全球生物多樣性框架中必須強烈反映環境與健康的聯結。這意味著與野生動物開發和自然對人類的貢獻有關之任何文本中應明確地包括溢出之預防。未能將這些點聯繫起來，會削弱圍繞在保護和可持續利用資源以實現公約本身目標的能力。
–
–
預防性的衛生照護
對災難反應式的回應不必然是常態。在許多國家，慢性病的預防性保健因其明顯的健康和經濟效益而受到廣泛接受。例如，使用結腸鏡檢查或其他方法篩查的每 1,000 人中可避免數十例結直腸癌死亡。預防方法不會減損在疾病發生時治療的重要性。
現在所有壓力源都被置於生物圈——以及這對人類健康所產生的負面影響——領導者迫切需要將這種思維方式應用於大流行上。
自然期刊 605, 419-422 (2022)
doi：https://doi.org/10.1038/d41586-022-01312-y
Want to prevent pandemics? Stop spillovers
Decision-makers discussing landmark agreements on health and biodiversity must include four actions to reduce the risk of animals and people exchanging viruses.
Cattle encroach on the Amazon rainforest in Brazil as trees are burnt to clear land for grazing.
Credit: Bruno Kelly/Reuters/Alamy
Spillover events, in which a pathogen that originates in animals jumps into people, have probably triggered every viral pandemic that’s occurred since the start of the twentieth century. What’s more, an August 2021 analysis of disease outbreaks over the past four centuries indicates that the yearly probability of pandemics could increase several-fold in the coming decades, largely because of human-induced environmental changes.
Fortunately, for around US$20 billion per year, the likelihood of spillover could be greatly reduced. This is the amount needed to halve global deforestation in hotspots for emerging infectious diseases; drastically curtail and regulate trade in wildlife; and greatly improve the ability to detect and control infectious diseases in farmed animals.
That is a small investment compared with the millions of lives lost and trillions of dollars spent in the COVID-19 pandemic. The cost is also one-twentieth of the statistical value of the lives lost each year to viral diseases that have spilled over from animals since 1918 (see ‘Spillovers: a growing threat’), and less than one-tenth of the economic productivity erased per year.
Source: Ref. 1
Yet many of the international efforts to better defend the world from future outbreaks, prompted by the COVID-19 pandemic, still fail to prioritize the prevention of spillover. Take, for example, the Independent Panel for Pandemic Preparedness and Response, established by the World Health Organization (WHO). The panel was convened in September 2020, in part to ensure that any future infectious-disease outbreak does not become another pandemic. In its 86-page report released last May, wildlife is mentioned twice; deforestation once.
We urge the decision-makers currently developing three landmark international endeavours to make the prevention of spillover central to each.
First, the G20 group of the world’s 20 largest economies provisionally agreed last month to create a global fund for pandemics. If realized, this could provide funding at levels that infectious-disease experts have been recommending for decades — around $5 per person per year globally. Second, an agreement to improve global approaches to pandemics is under discussion by the World Health Assembly (WHA), the decision-making body of the WHO. Third, a draft framework for biodiversity conservation — the post-2020 global biodiversity framework — is being negotiated by parties to the Convention on Biological Diversity.
Designed in the right way, these three international endeavours could foster a more proactive global approach to infectious diseases. This opportunity — to finally address the factors that drive major disease outbreaks, many of which also contribute to climate change and biodiversity loss — might not present itself again until the world faces another pandemic.
Four actions
The risk of spillover is greater when there are more opportunities for animals and humans to make contact, for instance in the trade of wildlife, in animal farming or when forests are cleared for mining, farming or roads. It is also more likely to happen under conditions that increase the likelihood of infected animals shedding viruses – when they are housed in cramped conditions, say, or not fed properly.
Decades of research from epidemiology, ecology and genetics suggest that an effective global strategy to reduce the risk of spillover should focus on four actions.
First, tropical and subtropical forests must be protected. Various studies show that changes in the way land is used, particularly tropical and subtropical forests, might be the largest driver of emerging infectious diseases of zoonotic origin globally4. Wildlife that survives forest clearance or degradation tends to include species that can live alongside people, and that often host pathogens capable of infecting humans. For example, in Bangladesh, bats that carry Nipah virus — which can kill 40–75% of people infected — now roost in areas of high human population density because their forest habitat has been almost entirely cleared.
Furthermore, the loss of forests is driving climate change. This could in itself aid spillover by pushing animals, such as bats, out of regions that have become inhospitable and into areas where many people live.
Yet forests can be protected even while agricultural productivity is increased — as long as there is enough political will and resources. This was demonstrated by the 70% reduction in deforestation in the Amazon during 2004–12, largely through better monitoring, law enforcement and the provision of financial incentives to farmers. (Deforestation rates began increasing in 2013 due to changes in environmental legislation, and have risen sharply since 2019 during Jair Bolsonaro’s presidency.)
Second, commercial markets and trade of live wild animals that pose a public-health risk must be banned or strictly regulated, both domestically and internationally.
Doing this would be consistent with the call made by the WHO and other organizations in 2021 for countries to temporarily suspend the trade in live caught wild mammals, and to close sections of markets selling such animals. Several countries have already acted along these lines. In China, the trade and consumption of most terrestrial wildlife has been banned in response to COVID-19. Similarly, Gabon has prohibited the sale of certain mammal species as food in markets.
A worker in a crowded chicken farm in Anhui province, China.Credit: Jianan Yu/Reuters
Restrictions on urban and peri-urban commercial markets and trade must not infringe on the rights and needs of Indigenous peoples and local communities, who often rely on wildlife for food security, livelihoods and cultural practices. There are already different rules for hunting depending on the community in many countries, including Brazil, Canada and the United States.
Third, biosecurity must be improved when dealing with farmed animals. Among other measures, this could be achieved through better veterinary care, enhanced surveillance for animal disease, improvements to feeding and housing animals, and quarantines to limit pathogen spread.
Poor health among farmed animals increases their risk of becoming infected with pathogens — and of spreading them. And nearly 80% of livestock pathogens can infect multiple host species, including wildlife and humans.
Fourth, particularly in hotspots for the emergence of infectious diseases, people’s health and economic security should be improved.
People in poor health — such as those who have malnutrition or uncontrolled HIV infection — can be more susceptible to zoonotic pathogens. And, particularly in immunosuppressed individuals such as these, pathogens can mutate before being passed on to others.
What’s more, some communities — especially those in rural areas — use natural resources to produce commodities or generate income in a way that brings them into contact with wildlife or wildlife by-products. In Bangladesh, for example, date palm sap, which is consumed as a drink in various forms, is often collected in pots attached to palm trees. These can become contaminated with bodily substances from bats. A 2016 investigation linked this practice to 14 Nipah virus infections in humans that caused 8 deaths.
Providing communities with both education and tools to reduce the risk of harm is crucial. Tools can be something as simple as pot covers to prevent contamination of date palm sap, in the case of the Bangladesh example.
In fact, providing educational opportunities alongside health-care services and training in alternative livelihood skills, such as organic agriculture, can help both people and the environment. For instance, the non-governmental organization Health in Harmony in Portland, Oregon, has invested in community-designed interventions in Indonesian Borneo. During 2007–17, these contributed to a 90% reduction in the number of households that were reliant on illegal logging for their main livelihood. This, in turn, reduced local rainforest loss by 70%. Infant mortality also fell by 67% in the programme’s catchment area.
Systems-oriented interventions of this type need to be better understood, and the most effective ones scaled up.
Wise investment
Such strategies to prevent spillover would reduce our dependence on containment measures, such as human disease surveillance, contact tracing, lockdowns, vaccines and therapeutics. These interventions are crucial, but are often expensive and implemented too late — in short, they are insufficient when used alone to deal with emerging infectious diseases.
The COVID-19 pandemic has exposed the real-world limitations of these reactive measures — particularly in an age of disinformation and rising populism. For example, despite the US federal government spending more than $3.7 trillion on its pandemic response as of the end of March, nearly one million people in the United States — or around one in 330 — have died from COVID-19. Globally, between 15 million and 21 million lives are estimated to have been lost during the COVID-19 pandemic beyond what would be expected under non-pandemic conditions (known as excess deaths). And a 2021 model indicates that, by 2025, $157 billion will have been spent on COVID-19 vaccines alone .
A farmer in Myanmar gathers sap from a palm tree to make wine. Contamination of the collection pots with excretions from bats can spread diseases to humans.Credit: Wolfgang Kaehler/LightRocket via Getty
Preventing spillover also protects people, domesticated animals and wildlife in the places that can least afford harm — making it more equitable than containment. For example, almost 18 months since COVID-19 vaccines first became publicly available, only 21% of the total population of Africa has received at least one dose. In the United States and Canada, the figure is nearly 80%. Meanwhile, Pfizer’s total drug sales rose from $43 billion in 2020 to $72 billion in 2021, largely because of the company’s COVID-19 vaccine, the best-selling drug of 2021.
Lastly, unlike containment measures, actions to prevent spillover also help to stop spillback, in which zoonotic pathogens move back from humans to animals and then jump again into people. Selection pressures can differ across species, making such jumps a potential source of new variants that can evade existing immunity. Some researchers have suggested that spillback was possibly responsible for the emergence of the Omicron variant of SARS-CoV-2.
Seize the day
Over the past year, the administration of US President Joe Biden and two international panels (one established in 2020 by the WHO and the other in 2021 by the G20) have released guidance on how to improve approaches to pandemics. All recommendations released so far acknowledge spillover as the predominant cause of emerging infectious diseases. None adequately discusses how that risk might be mitigated. Likewise, a PubMed search for the spike protein of SARS-CoV-2 yields thousands of papers, yet only a handful of studies investigate coronavirus dynamics in bats, from which SARS-CoV-2 is likely to have originated.
Spillover prevention is probably being overlooked for several reasons. Upstream animal and environmental sources of pathogens might be being neglected by biomedical researchers and their funders because they are part of complex systems — research into which does not tend to lead to tangible, profitable outputs. Also, most people working in public health and biomedical sciences have limited training in ecology, wildlife biology, conservation and anthropology.
Climate change will force new animal encounters — and boost viral outbreaks
There is growing recognition of the importance of cross-sectoral collaboration, including soaring advocacy for the ‘One Health’ approach — an integrated view of health that recognizes links between the environment, animals and humans. But, in general, this has yet to translate into action to prevent pandemics.
Another challenge is that it can take decades to realize the benefits of preventing spillover, instead of weeks or months for containment measures. Benefits can be harder to quantify for spillover prevention, no matter how much time passes, because, if measures are successful, no outbreak occurs. Prevention also runs counter to individual, societal and political tendencies to wait for a catastrophe before taking action.
The global pandemic fund, the WHA pandemic agreement and the post-2020 global biodiversity framework all present fresh chances to shift this mindset and put in place a coordinated global effort to reduce the risk of spillover alongside crucial pandemic preparedness efforts.
Global fund for pandemics
First and foremost, a global fund for pandemics will be key to ensuring that the wealth of evidence on spillover prevention is translated into action. Funding for spillover prevention should not be folded into existing conservation funds, nor draw on any other existing funding streams.
Investments must be targeted to those regions and practices where the risk of spillover is greatest, from southeast Asia and Central Africa to the Amazon Basin and beyond. Actions to prevent spillover in these areas, particularly by reducing deforestation, would also help to mitigate climate change and reduce loss of biodiversity. But conservation is itself drastically underfunded. As an example, natural solutions (such as conservation, restoration and improved management of forests, wetlands and grasslands) represent more than one-third of the climate mitigation needed by 2030 to stabilize warming to well below 2 °C. Yet these approaches receive less than 2% of global funds for climate mitigation. (Energy systems receive more than half.)
In short, the decision-makers backing the global fund for pandemics must not assume that existing funds are dealing with the threat of spillover — they are not. The loss of primary tropical forest was 12% higher in 2020 than in 2019, despite the economic downturn triggered by COVID-19. This underscores the continuing threat to forests.
Funding must be sustained for decades to ensure that efforts to reduce the risk of spillover are in place long enough to yield results.
WHA pandemic agreement
In 2020, the president of the European Council, Charles Michel, called for a treaty to enable a more coordinated global response to major epidemics and pandemics. Last year, more than 20 world leaders began echoing this call, and the WHA launched the negotiation of an agreement (potentially, a treaty or other international instrument) to “strengthen pandemic prevention, preparedness, and response” at the end of 2021.
Such a multilateral agreement could help to ensure more-equitable international action around the transfer of scientific knowledge, medical supplies, vaccines and therapeutics. It could also address some of the constraints currently imposed on the WHO, and define more clearly the conditions under which governments must notify others of a potential disease threat. The COVID-19 pandemic exposed the shortcomings of the International Health Regulations on many of these fronts. (This legal framework defines countries’ rights and obligations in the handling of public-health events and emergencies that could cross borders.)
One Health approaches require community engagement, education, and international collaborations—a lesson from Rwanda
We urge negotiators to ensure that the four actions to prevent spillover outlined here are prioritized in the WHA pandemic agreement. For instance, it could require countries to create national action plans for pandemics that include reducing deforestation and closing or strictly regulating live wildlife markets. A reporting mechanism should also be developed to evaluate progress in implementing the agreement. This could build on experience from existing schemes, such as the WHO Joint External Evaluation process (used to assess countries’ capacities to handle public-health risks) and the verification regime of the Chemical Weapons Convention.
Commitments to expand pathogen surveillance at interfaces between humans, domesticated animals and wildlife — from US mink farms and Asian wet markets to areas of high deforestation in South America — should also be wrapped into the WHA agreement. Surveillance will not prevent spillover, but it could enable earlier detection and better control of zoonotic outbreaks, and provide a better understanding of the conditions that cause them. Disease surveillance would improve simply through investing in clinical care for both people and animals in emerging infectious-disease hotspots.
Convention on Biological Diversity
We are in the midst of the sixth mass extinction, and activities that drive the loss of biodiversity, such as deforestation, also contribute to the emergence of infectious disease. Mea