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      美國迎來第五波疫情,疫苗保護力卻在減弱

      美國迎來第五波疫情,疫苗保護力卻在減弱

      Erin Prater 2022-05-19
      人們的確不斷意識到,無論是因為接種疫苗還是曾經感染,獲得的免疫力都會隨著時間的推移而減弱。

      打或不打第二劑加強針,至少對一部分人來說,這是個問題。

      大多數的美國人還無法選擇接種第二劑新冠肺炎疫苗加強針。5月13日,《財富》雜志詢問美國疾病控制與預防中心(U.S. Centers for Disease Control and Prevention),為什么還沒有針對多數人群打第二針加強針出臺指導意見,預計什么時候出臺,該中心并未給出明確回答。

      然而,對于那些符合接種條件的人(主要是老年人和免疫功能低下者),它確實提出了最新的指導意見,敦促他們考慮自身可能因為基礎病和社交接觸而導致感染新冠病毒后出現“重癥”。該聯邦機構修訂后的意見是:在打第四針前要三思。此時此刻,由于新冠肺炎基金的撥付在美國國會陷入僵局,人們擔心美國政府可能會定量減少疫苗供應配給。

      對于符合接種條件的人來說,第二針加強針值得打嗎?沒有資格接種的人是不是錯失了良機?特別是,當前正值第五波新冠肺炎疫情來襲,而白宮預計今年秋冬會再次出現疫情。

      “第二針加強針的作用還不確定?!盕ractal Therapeutics的首席執行官、新冠肺炎研究人員阿里吉特·查克拉瓦蒂說,“作用似乎不大,而且持續時間很短。但如果你想通過‘瑞士奶酪’策略來加強個人防護,它相當于又多了一層保護。從這個角度看,這是值得的?!?/p>

      “多多少少有點效果”

      約翰斯·霍普金斯大學布隆伯格公共衛生學院(Johns Hopkins Bloomberg School of Public Health)的流行病學家凱里·阿爾托夫稱,是否推薦大多數美國人打第二針加強針是一個很復雜的問題。

      “如果不能確定一樣東西的利大于弊,我們就不想推薦?!彼?月13日向《財富》雜志表示,“盡管mRNA疫苗的安全性十分高,但我們仍然希望確保這些疫苗可以有效地讓人們遠離醫院、免于死亡?!?/p>

      “更進一步,我們還要確保這些疫苗在病毒發生變化時仍然有效?!?/p>

      據《華盛頓郵報》(Washington Post)最近報道,在今年1月和2月的首波奧密克戎疫情中,因為新冠病毒而死亡的人中,接種了疫苗的人占一半,高于去年秋天德爾塔變種爆發時期23%的數字。

      阿爾托夫稱在沒有看到背后的數據之前,不會對《華盛頓郵報》的上述報道發表評論。但人們的確不斷意識到,無論是因為接種疫苗還是曾經感染,獲得的免疫力都會隨著時間的推移而減弱。

      “我們知道免疫力在大約四個月后開始減弱,而當前的主流病毒變種具有更強的突破能力?!眰魅静<?、哥倫比亞大學瓦格洛斯醫師和外科醫生學院(Columbia University Vagelos College of Physicians and Surgeons)的醫學助理教授馬庫斯·佩雷拉博士在今年4月的一篇博客中寫道。

      他引用了以色列于4月發表在《新英格蘭醫學雜志》(The New England Journal of Medicine)上的一項研究說:“如果是想保護年輕人免患重癥,第四針似乎無法帶來太多好處?!毖芯堪l現,醫護人員在接種第二針加強針后,抗體平均會恢復到打完第一針加強針后的水平。沒有打第二針的醫護人員的抗體水平則繼續下降。

      然而,第二針加強針并沒有大幅減少最終感染奧密克戎的幾率:接種了第二針加強針的受試者中,約20%的人感染了病毒,而只打了一針的人中,感染比例為25%。所有感染了病毒的受試者,無論打了幾針加強針,都出現了輕微癥狀,而且呈現出高病毒載量,也就是說他們很可能具有傳染性。

      該研究稱第二針加強針是“可以產生免疫反應的”、“安全的”,但只是“稍微有點效,主要是針對有癥狀的疾病”。該研究未能為在年輕人和健康人群中接種第四針疫苗提供有力依據。

      查克拉瓦蒂指出,將人們按照免疫功能是否受損進行劃分存在一個問題,即“人與人之間的免疫應答強度存在很大異質性”,他補充道,他的研究團隊很快將就此發表一篇論文。

      “它的鐘形曲線非常寬。有些人中和抗體的半衰期非常非常短;有些人則很長。無法把人整齊地分成兩類?!?/p>

      “轉瞬即逝”的效果

      查克拉瓦蒂引用5月13日發表在《美國醫學會雜志網絡開放》(JAMA Network Open)上的一項研究說,雖然加強針恢復了對重癥的預防能力,但“持續時間相當短”。該研究發現,接種完第三針疫苗后,對奧密克戎的免疫力僅在幾周后就開始下降,而打完前兩針后幾個月才開始減弱,稱加強針的抗體反應是“轉瞬即逝的”。

      但這不僅僅與一個人對重復接種疫苗的免疫應答有關。

      “你的身體對每一次接種的反應都不同,但病毒同樣也在做出反應?!彼f。

      奧密克戎變種越來越善于躲避曾經感染和接種疫苗產生的免疫保護。最近的一項研究發現,那些之前感染過奧密克戎BA.1毒株但沒有接種疫苗的人,在接觸到最近席卷南非的新變種BA.4和B.5毒株時,中和抗體的水平下降了近八倍。該研究顯示,那些既接種了疫苗又感染過的人,中和抗體水平下降了三倍。

      查克拉瓦蒂說,一開始,人們希望,針對原始毒株的抗體能夠抵抗未來的變種和亞變種,“但病毒在夜以繼日地努力解決這個問題?!?/p>

      查克拉瓦蒂建議,還沒有打過第一針加強針的人要去打,如果有一天可以再次打加強針了,也要繼續接種。

      “我自己嗎?我會再打一針加強針?!彼f,“會有什么驚艷的效果嗎?不。我認為大多數人都沒有注意到,事實上,疫苗正在逐漸失去——幾乎已經完全失去——預防感染的能力。它們也可能正在失去抵御重癥的能力?!?/p>

      “不管打不打第二針加強針,六個月后,我們或多或少又會陷入同樣的境地?!?/p>

      查克拉瓦蒂說,疫苗遠非速戰速決之計,而是對抗新冠肺炎病毒武器庫中的其中一件工具。如果希望減少感染這種有時會致命的病毒的幾率,以及減少患上可能致殘的“長新冠”的可能性,也可以戴上像N95這樣的高質量口罩。

      “目前唯一最有效的干預措施就是戴口罩?!彼f?!斑@是一個不幸的事實,因為已經過去兩年了,我們早就應該越過這個關口了?!?/p>

      他想對那些有資格打第二針加強針的人說:“你要想清楚,如果你只能多獲得幾周或者幾個月的額外保護,什么時候打對你最合適?”

      “這就是目前為止你能夠得到的。當然,實際結果也可能不同于預期,因為下一個變種或許也具有逃逸能力?!保ㄘ敻恢形木W)

      譯者:Agatha

      打或不打第二劑加強針,至少對一部分人來說,這是個問題。

      大多數的美國人還無法選擇接種第二劑新冠肺炎疫苗加強針。5月13日,《財富》雜志詢問美國疾病控制與預防中心(U.S. Centers for Disease Control and Prevention),為什么還沒有針對多數人群打第二針加強針出臺指導意見,預計什么時候出臺,該中心并未給出明確回答。

      然而,對于那些符合接種條件的人(主要是老年人和免疫功能低下者),它確實提出了最新的指導意見,敦促他們考慮自身可能因為基礎病和社交接觸而導致感染新冠病毒后出現“重癥”。該聯邦機構修訂后的意見是:在打第四針前要三思。此時此刻,由于新冠肺炎基金的撥付在美國國會陷入僵局,人們擔心美國政府可能會定量減少疫苗供應配給。

      對于符合接種條件的人來說,第二針加強針值得打嗎?沒有資格接種的人是不是錯失了良機?特別是,當前正值第五波新冠肺炎疫情來襲,而白宮預計今年秋冬會再次出現疫情。

      “第二針加強針的作用還不確定?!盕ractal Therapeutics的首席執行官、新冠肺炎研究人員阿里吉特·查克拉瓦蒂說,“作用似乎不大,而且持續時間很短。但如果你想通過‘瑞士奶酪’策略來加強個人防護,它相當于又多了一層保護。從這個角度看,這是值得的?!?/p>

      “多多少少有點效果”

      約翰斯·霍普金斯大學布隆伯格公共衛生學院(Johns Hopkins Bloomberg School of Public Health)的流行病學家凱里·阿爾托夫稱,是否推薦大多數美國人打第二針加強針是一個很復雜的問題。

      “如果不能確定一樣東西的利大于弊,我們就不想推薦?!彼?月13日向《財富》雜志表示,“盡管mRNA疫苗的安全性十分高,但我們仍然希望確保這些疫苗可以有效地讓人們遠離醫院、免于死亡?!?/p>

      “更進一步,我們還要確保這些疫苗在病毒發生變化時仍然有效?!?/p>

      據《華盛頓郵報》(Washington Post)最近報道,在今年1月和2月的首波奧密克戎疫情中,因為新冠病毒而死亡的人中,接種了疫苗的人占一半,高于去年秋天德爾塔變種爆發時期23%的數字。

      阿爾托夫稱在沒有看到背后的數據之前,不會對《華盛頓郵報》的上述報道發表評論。但人們的確不斷意識到,無論是因為接種疫苗還是曾經感染,獲得的免疫力都會隨著時間的推移而減弱。

      “我們知道免疫力在大約四個月后開始減弱,而當前的主流病毒變種具有更強的突破能力?!眰魅静<?、哥倫比亞大學瓦格洛斯醫師和外科醫生學院(Columbia University Vagelos College of Physicians and Surgeons)的醫學助理教授馬庫斯·佩雷拉博士在今年4月的一篇博客中寫道。

      他引用了以色列于4月發表在《新英格蘭醫學雜志》(The New England Journal of Medicine)上的一項研究說:“如果是想保護年輕人免患重癥,第四針似乎無法帶來太多好處?!毖芯堪l現,醫護人員在接種第二針加強針后,抗體平均會恢復到打完第一針加強針后的水平。沒有打第二針的醫護人員的抗體水平則繼續下降。

      然而,第二針加強針并沒有大幅減少最終感染奧密克戎的幾率:接種了第二針加強針的受試者中,約20%的人感染了病毒,而只打了一針的人中,感染比例為25%。所有感染了病毒的受試者,無論打了幾針加強針,都出現了輕微癥狀,而且呈現出高病毒載量,也就是說他們很可能具有傳染性。

      該研究稱第二針加強針是“可以產生免疫反應的”、“安全的”,但只是“稍微有點效,主要是針對有癥狀的疾病”。該研究未能為在年輕人和健康人群中接種第四針疫苗提供有力依據。

      查克拉瓦蒂指出,將人們按照免疫功能是否受損進行劃分存在一個問題,即“人與人之間的免疫應答強度存在很大異質性”,他補充道,他的研究團隊很快將就此發表一篇論文。

      “它的鐘形曲線非常寬。有些人中和抗體的半衰期非常非常短;有些人則很長。無法把人整齊地分成兩類?!?/p>

      “轉瞬即逝”的效果

      查克拉瓦蒂引用5月13日發表在《美國醫學會雜志網絡開放》(JAMA Network Open)上的一項研究說,雖然加強針恢復了對重癥的預防能力,但“持續時間相當短”。該研究發現,接種完第三針疫苗后,對奧密克戎的免疫力僅在幾周后就開始下降,而打完前兩針后幾個月才開始減弱,稱加強針的抗體反應是“轉瞬即逝的”。

      但這不僅僅與一個人對重復接種疫苗的免疫應答有關。

      “你的身體對每一次接種的反應都不同,但病毒同樣也在做出反應?!彼f。

      奧密克戎變種越來越善于躲避曾經感染和接種疫苗產生的免疫保護。最近的一項研究發現,那些之前感染過奧密克戎BA.1毒株但沒有接種疫苗的人,在接觸到最近席卷南非的新變種BA.4和B.5毒株時,中和抗體的水平下降了近八倍。該研究顯示,那些既接種了疫苗又感染過的人,中和抗體水平下降了三倍。

      查克拉瓦蒂說,一開始,人們希望,針對原始毒株的抗體能夠抵抗未來的變種和亞變種,“但病毒在夜以繼日地努力解決這個問題?!?/p>

      查克拉瓦蒂建議,還沒有打過第一針加強針的人要去打,如果有一天可以再次打加強針了,也要繼續接種。

      “我自己嗎?我會再打一針加強針?!彼f,“會有什么驚艷的效果嗎?不。我認為大多數人都沒有注意到,事實上,疫苗正在逐漸失去——幾乎已經完全失去——預防感染的能力。它們也可能正在失去抵御重癥的能力?!?/p>

      “不管打不打第二針加強針,六個月后,我們或多或少又會陷入同樣的境地?!?/p>

      查克拉瓦蒂說,疫苗遠非速戰速決之計,而是對抗新冠肺炎病毒武器庫中的其中一件工具。如果希望減少感染這種有時會致命的病毒的幾率,以及減少患上可能致殘的“長新冠”的可能性,也可以戴上像N95這樣的高質量口罩。

      “目前唯一最有效的干預措施就是戴口罩?!彼f?!斑@是一個不幸的事實,因為已經過去兩年了,我們早就應該越過這個關口了?!?/p>

      他想對那些有資格打第二針加強針的人說:“你要想清楚,如果你只能多獲得幾周或者幾個月的額外保護,什么時候打對你最合適?”

      “這就是目前為止你能夠得到的。當然,實際結果也可能不同于預期,因為下一個變種或許也具有逃逸能力?!保ㄘ敻恢形木W)

      譯者:Agatha

      To boost again or not to boost again. That is the question—for some, at least.

      A second COVID booster currently isn’t an option for most Americans. When asked by Fortune on May 13 why guidance has not yet been released for second boosters for a majority of people, or when it would be, the U.S. Centers for Disease Control failed to answer specifically.

      It did, however, point to updated guidance for those who are eligible—the elderly and immunocompromised, mainly—urging them to consider how likely they are to get “very sick” from the virus based on preexisting health issues and community exposure. The federal agency’s revised message: Think twice before scheduling a fourth jab. It comes amid concerns that the U.S. government may be rationing a dwindling supply of vaccines as potential new COVID funding stalls in Congress.

      For those who are eligible, is a second booster worth it? And are those who are ineligible missing out—especially during a fifth COVID wave, with yet another predicted by the White House this fall and winter?

      “A second booster is sort of on the bubble,” said Arijit Chakravarty, a COVID researcher and CEO of Fractal Therapeutics. “The effects seem small and short lived. But if you’re implementing your own ‘swiss cheese’ strategy, it’s one more layer. In that respect, it’s worthwhile.”

      “Somewhat efficacious”

      The question of whether to recommend a second booster for most Americans is complicated, said Keri Althoff, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

      “We don’t want to recommend anything that isn’t going to confer more benefit than potential harm,” she told Fortune on May 13. “Although mRNA vaccines have an incredible safety profile, we still want to make sure that these vaccines are working effectively to keep people out of the hospital or protect people from death.”

      “Even better, we need to make sure these vaccines are still doing it as the virus changes.”

      Those who had been vaccinated made up nearly half of COVID fatalities in January and February of this year during the initial Omicron surge—up from 23% during the Delta wave last fall, The Washington Post recently reported.

      Althoff wouldn’t comment on The Post’s reporting without seeing the data behind it. But there is growing awareness that immunity—whether from vaccination or previous infection—wanes with time.

      “We know immunity starts to wane after four months or so, and we have a variant circulating that is more capable of breaking through our immunity,” Dr. Marcus Pereira, an infectious disease expert and assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, said in an April blog post.

      “A fourth booster does not seem to create much of a benefit when it comes to more severe outcomes for those who are younger,” he said, citing an April study out of Israel published in The New England Journal of Medicine. It found that among health care workers who received a second booster, antibodies were restored to levels around those typically seen after a first booster. Among health care workers who weren’t boosted a second time, antibody levels continue to wane.

      A second booster, however, didn’t significantly reduce the percentage of those who eventually developed Omicron—around 20% of those who received a second booster, as compared to 25% of those who had been boosted only once. All participants who developed COVID, regardless of how many boosters they’d received, experienced minimal symptoms but saw high viral loads, meaning they were likely infectious.

      The study called a second booster “immunogenic” and “safe” but only “somewhat efficacious, primarily against symptomatic disease.” It failed to make a strong case for a fourth vaccine in the young and healthy.

      The trouble with placing individuals in two categories—immunocompromised and not—is that there is “a lot of person to person heterogeneity in the strength of immune response,” Chakravarty said, adding that his research team would soon be publishing a paper on the topic.

      “It lives on a very wide bell curve. Some people have a very, very short half life for neutralizing antibodies; some have very long half lives. They don’t neatly break down into two buckets.”

      “Transient” benefit

      While boosters restore protection against severe disease, “the duration is quite a bit shorter,” said Chakravarty, citing a study published to JAMA Network Open on May 13. It found a decline in vaccine efficacy against Omicron just weeks after a third dose, versus months after the initial two-dose regime, calling the antibody response after a booster “transient.”

      But there’s more at play than one’s ability to mount a response to repeated vaccinations.

      “Your body is responding differently to each new dose, but the virus is also reacting,” he said.

      Omicron subvariants have become increasingly adept at evading immunity from both prior infection and vaccination. A recent study found that those who had been previously infected with Omicron BA.1 but not vaccinated suffered a nearly eightfold drop in neutralizing antibodies when exposed to BA.4 and B.5, the new Omicron variants sweeping South Africa. Those who had been vaccinated and previously infected saw a milder threefold decrease, according to the study.

      The initial hope was that antibodies against the Wuhan strain of COVID would hold up against future variants and subvaraints, “but the virus is working night and day to solve that problem,” Chakravarty said.

      Those who’ve yet to receive a first booster shot should do so, Chakravarty advised, and boost again if they’re eventually able.

      “Me, personally? I’ll get a second booster,” he said. “Is it going to be amazing? No. I think most people missed the memo that the vaccines are, in fact, fading—have almost completely faded—in the ability to protect against infection. They may also be losing the ability to protect against severe disease as well.”

      “Get the second booster or don’t—but either way, six months down the road, we’re all in the same bucket again, more or less.”

      Far from a quick fix, vaccines are a tool in an arsenal of weapons against COVID, Chakravarty said. Those who wish to decrease their chances of contracting the sometimes deadly virus—and of developing a potentially disabling case of Long COVID—can also wear a quality mask like an N95.

      “Right now the single most effective intervention is to wear a mask,” he said. “That's unfortunate, because two years in, we should have been past this point.”

      His message to those eligible for a second booster: “You need to figure out, if you’ve only got a few weeks of added protection, or a few months, when is the right time for you?” he said.

      “That’s what you’re going to get as of now. Your mileage may vary, because the next variant may be able to evade that as well.”

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