全球範圍內的脊髓灰質炎爆發讓科學家們保持警惕

美國和以色列的癱瘓病例顯示，疫苗衍生的脊髓灰質炎病毒已經感染了許多人。

資料來源： Heidi Ledford / 新聞解釋者 / 2022 年 8 月 22 日 / 自然 / 財團法人台灣紅絲帶基金會編譯

 

廣泛使用的脊髓灰質炎口服活疫苗中的病毒在極少數情況下會變異成能夠感染神經系統的危險形式。圖片來源: Ezra Acayan/Getty

 

今年在紐約州、倫敦和耶路撒冷發現脊髓灰質炎病毒讓許多人感到意外——但努力根除這種疾病的公共衛生研究人員表示，這只是時間問題。

「世界上沒有一個國家可以免受脊髓灰質炎的影響」，巴基斯坦卡拉奇阿加汗大學的全球健康研究員 Zulfiqar Bhutta 說。「這一切都是相互關聯的」。

 

 

脊髓灰質炎在英國的存在對全球健康意味著什麼

在這些地區發現的病毒源自於一些國家使用的口服脊髓灰質炎疫苗。迄今為止，僅報告了兩例與脊髓灰質炎相關的麻痺病例，分別是 2 月在耶路撒冷和 6 月在紐約；紐約感染是近十年來美國首例此類病例。但所有三個地區的廢水樣本都表明該病毒的傳播範圍更廣。

喬治亞州亞特蘭大埃默里大學研究傳染病的沃爾特·奧倫斯坦說，脊髓灰質炎在不到 200 個易感人群中導致不可逆轉的麻痺，因此麻痺病例顯示那裡的許多其他人已經被感染。「這樣的案例只是冰山一角」，他說。「這非常令人擔憂」。

《自然》期刊與研究人員討論了疫情的規模，以及可以採取哪些措施來阻止它。

為什麼會發生這些疫情？

野生脊髓灰質炎病毒僅在阿富汗和巴基斯坦這兩個國家傳播，截至今年 6 月，這兩個國家已報告了 9 例病例。

但疫苗衍生的脊髓灰質炎病毒會在其他地方定期出現，特別是在非洲和亞洲。這些病例來自一種廣泛使用的口服疫苗，該疫苗含有活的、弱化的病毒，有時會變異為能夠感染神經系統的危險形式。

美國和英國都沒有使用這種疫苗，而是選擇了一種含有滅活病毒的注射疫苗。加州大學舊金山分校的微生物學家 Raul Andino-Pavlovsky 說，這種疫苗可以防止病毒感染神經系統，但在減少病毒脫落和阻止傳播方面不如口服病毒有效。

英國、以色列和美國的脊髓灰質炎疫苗接種率很高，這意味著大多數兒童不會受到病毒的最壞影響（美國 5 歲和 6 歲兒童中約有 94% 接種了疫苗）。但是未接種疫苗的人很容易感染這種疾病。

「這種病毒非常非常擅長尋找未接種疫苗的個」，奧倫斯坦說。瑞士日內瓦的世界衛生組織 (WHO)全球根除脊髓灰質炎倡議發言人奧利弗·羅森鮑爾（Oliver Rosenbauer）說，儘管荷蘭的總體疫苗接種覆蓋率超過 90%，但 1990 年代，脊髓灰質炎病毒爆發在該國的一個疫苗接種率相對較低的社區中站穩了腳跟。此次疫情導致 2 人死亡和 59 人癱瘓，事件發生在該國最後一例地方性脊髓灰質炎病例 14 年後。

脊髓灰質炎病毒是否已經擴散到首次發現的地區之外？

小兒麻痺症廢水監測在富裕國家很少見；英國僅在倫敦和格拉斯哥定期監測污水中的疾病。在官員了解到與脊髓灰質炎相關的癱瘓案例後，紐約於 7 月開始測試廢水。

因此，目前尚不清楚該病毒可能傳播了多遠。但有理由希望它並沒有走遠：在倫敦，自 2 月以來一直在污水中檢測到脊髓灰質炎病毒，該病毒似乎仍然集中在該市的北部和東部，並且沒有關於脊髓灰質炎的報告——相關癱瘓。倫敦帝國理工學院的傳染病流行病學家 Nicholas Grassly 說：「即使在倫敦，它似乎也相當局部化」。

奧倫斯坦說，在紐約，該病毒已在兩個縣以及紐約市檢測到，這種地理傳播「非常令人擔憂」。 「這顯示我們已經有了大量傳播」。

美國疾病控制和預防中心 (CDC) 將優先對與麻痺病例有關的疫苗接種不足社區的小兒麻痺症廢水監測。「從廢水樣本中檢測脊髓灰質炎病毒非常耗費人力和資源」，CDC 發言人告訴《自然》期刊。但她補充說，為監測冠狀病毒 SARS-CoV-2 而建立的監測系統正在努力提供支持。

能控制住疫情嗎？

美國、以色列和英國都在加強疫苗接種工作，這應該會填補 COVID-19 大流行期間造成的空白。這包括一項雄心勃勃的努力，為倫敦所有 1 至 9 歲的兒童接種疫苗。

格拉斯利說，這種策略應該可將疫情扼殺在萌芽狀態。但倫敦和紐約的運動將使用注射型疫苗，因此它們不會阻止病毒傳播。

他說，如果在六個月左右的時間裡，廢水檢測表明脊髓灰質炎病毒繼續傳播，那麼可能有必要考慮其他選擇。例如，2020 年，世界衛生組織列出了一種新的口服脊髓灰質炎疫苗以供緊急使用。

這種疫苗含有弱化的脊髓灰質炎病毒。但研究人員利用病毒基因組上的知識——包括參與復制基因組中容易出錯的酶如何產生基因變化——創造了一套突變，以防止病毒重新獲得感染神經系統的能力。「這就像把病毒放在進化的籠子裡」，幫助設計疫苗的安迪諾-帕夫洛夫斯基說。

該疫苗尚未經過大規模人體試驗，也未獲得英國或美國監管機構的批准。但安迪諾-帕夫洛夫斯基說，已經有超過 1 億人接受了這種疫苗，而且沒有出現疫苗衍生脊髓灰質炎病毒的跡象。

其他地方的脊髓灰質炎疫情情況如何？

羅森鮑爾說，富裕國家的疫情引起了很多關注。「但在過去的 20 年裡，我們在世界各地的發展中國家已發生了許多嚴重的疫情Ｊ。”

羅森鮑爾說，儘管 COVID-19 造成了破壞，但有令人鼓舞的跡象表明，根除脊髓灰質炎的鬥爭正在取得進展。他說，葉門和非洲一些國家的疫情仍然活躍，但範圍正在縮小。

在發生武裝衝突的地方，例如阿富汗和葉門地區，接種疫苗很困難。他說：「我們需要政治意願來實施一項計畫，以覆蓋具有挑戰性地區的所有兒童」。否則，疾病將在全球範圍內捲土重來」。

 

doi：https://doi.org/10.1038/d41586-022-02233-6

參考文獻：

1. Link-Gelles，R. et al.。Morb. Mortal. Wkly Rep. 71, 1065–1068 (2022)。

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Spate of polio outbreaks worldwide puts scientists on alert

Cases of paralysis in the United States and Israel suggest vaccine-derived poliovirus has infected many people.

•Heidi Ledford / NEWS EXPLAINER / 22 August 2022

 

The virus in widely used live oral vaccine for polio can on rare occasions mutate into a dangerous form capable of infecting the nervous system.Credit: Ezra Acayan/Getty

 

The discovery of poliovirus in New York state, London and Jerusalem this year has taken many by surprise — but public-health researchers fighting to eradicate the disease say it was only a matter of time.

“No country in the world is immune to the effects of polio,” says Zulfiqar Bhutta, a global-health researcher at the Aga Khan University in Karachi, Pakistan. “It’s all interconnected.”

 

What polio’s UK presence means for global health

 

The virus found in these regions is derived from an oral polio vaccine used in some countries. So far, only two cases of polio-related paralysis have been reported, in Jerusalem in February and New York in June1; the New York infection was the first such US case in nearly a decade. But wastewater samples in all three areas suggest that the virus is circulating more widely.

Polio causes irreversible paralysis in less than one in 200 of the susceptible people it infects, so the cases of paralysis suggest that many other people there have been infected, says Walter Orenstein, who studies infectious diseases at Emory University in Atlanta, Georgia. “Cases like that are just the tip of the iceberg,” he says. “It’s very concerning.”

Nature talked to researchers about the scale of the outbreak, and what can be done to stop it.

Why are these outbreaks happening?

Wild poliovirus circulates in only two countries — Afghanistan and Pakistan — where this year nine cases had been reported by June.

But vaccine-derived poliovirus appears periodically elsewhere, particularly in Africa and Asia. These cases come from a widely used oral vaccine that contains live, weakened virus that sometimes mutates to a dangerous form capable of infecting the nervous system.

Neither the United States nor the United Kingdom use that vaccine, opting instead for an injectable vaccine containing inactivated virus. This vaccine can keep the virus from infecting the nervous system, but it is not as effective as the oral virus at reducing viral shedding and halting transmission, says Raul Andino-Pavlovsky, a microbiologist at the University of California, San Francisco.

High polio vaccination rates in the United Kingdom, Israel and the United States mean that most children will be spared the virus’s worst effects (about 94% of US 5- and 6-year-olds are vaccinated). But unvaccinated people are vulnerable to the illness.

“This virus is very, very good at finding unvaccinated individuals,” says Orenstein. In the 1990s, a poliovirus outbreak in the Netherlands established a foothold in a community with a relatively low vaccination rate, despite the country’s overall vaccination coverage of more than 90%, says Oliver Rosenbauer, a spokesperson for the Global Polio Eradication Initiative of the World Health Organization (WHO) in Geneva, Switzerland. The outbreak resulted in 2 deaths and 59 cases of paralysis, and occurred 14 years after the country’s last endemic case of polio.

Has poliovirus spread beyond the regions where it was first identified?

Wastewater surveillance for polio is rare in rich countries; the United Kingdom routinely monitors sewage for the disease only in London and Glasgow. And New York began testing waste water in July, after officials learnt about the case of polio-related paralysis.

So it’s unclear how far the virus might have spread. But there is reason to hope that it hasn’t gone far: in London, which has been detecting poliovirus in sewage since February, the virus seems to have remained concentrated in the city’s north and east, and there have been no reports of polio-related paralysis. “It appears to be fairly localized, even within London,” says infectious-disease epidemiologist Nicholas Grassly at Imperial College London.

In New York, the virus has been detected in two counties as well as New York City, a geographical spread that is “very concerning”, says Orenstein. “It suggests we have had substantial transmission.”

The US Centers for Disease Control and Prevention (CDC) will prioritize wastewater surveillance for polio in under-vaccinated communities linked to the paralysis case. “Poliovirus testing from wastewater samples is very labour- and resource-intensive,” a CDC spokesperson told Nature. But surveillance systems set up to monitor the coronavirus SARS-CoV-2 are working to provide support, she added.

Can the outbreaks be contained?

The United States, Israel and the United Kingdom are all boosting vaccination efforts, which should fill gaps created during the COVID-19 pandemic. This includes an ambitious effort to vaccinate all one-to-nine-year-olds in London.

This strategy should nip the outbreaks in the bud, says Grassly. But the campaigns in London and New York will use injectable vaccine, so they will not stop virus transmission.

If, in six months or so, wastewater testing suggests that poliovirus has continued to spread, it might be necessary to look at other options, he says. For example, in 2020, the WHO listed a new oral polio vaccine for emergency use.

This vaccine contains weakened poliovirus. But researchers used knowledge of the virus’s genome — including how an error-prone enzyme involved in replicating the genome can generate genetic changes — to create a suite of mutations that keep the virus from regaining its ability to infect the nervous system. “It’s like putting the virus in an evolutionary cage,” says Andino-Pavlovsky, who helped to design the vaccine.

That vaccine has not yet undergone large-scale human testing, and has not been approved by UK or US regulators. But more than 100 million people have received it, says Andino-Pavlovsky, with no signs of vaccine-derived poliovirus emerging.

What is the status of polio outbreaks elsewhere?

Outbreaks in wealthy countries get lots of attention, says Rosenbauer. “But over the past 20 years, we’ve had many, many serious outbreaks around the world in developing countries.”

Rosenbauer says there are encouraging signs that the battle to eradicate polio is making progress, despite the disruption caused by COVID-19. Outbreaks in Yemen and a few countries in Africa are still active, he says, but their range is shrinking.

In places where there is armed conflict, such as areas of Afghanistan and Yemen, vaccination is difficult. “We need the political will to implement a plan to reach all the children in challenging areas,” he says. Otherwise, “the disease will come back globally”.

doi: https://doi.org/10.1038/d41586-022-02233-6

References

1.Link-Gelles, R. et al. Morb. Mortal. Wkly Rep. 71, 1065–1068 (2022).