欧洲搞错了方向? 福奇称群体免疫或不适用于新冠

美国国家过敏与传染病研究所所长福奇（Anthony Fauci）近日撰文指出，目前欧洲许多国家主张群体免疫，传统的群体免疫概念可能不适用于新冠病毒，并表示这意味着相当长一段时间内，新冠病毒不会在人群中消失。

　　根据《CNN》今 ( 16 ) 日报导，福奇最近在《传染病学期刊》上与学者合作撰写一篇关于“群体免疫”的论文，针对群体免疫可能无效佛奇进一步解释。

　　他举麻疹为例，麻疹病毒也是透过空气传播，若无免疫力 10 人中有 9 人会被感染，传染力相当于 Omicron 变异株。

　　而美国成功阻止麻疹病毒传播的原因有三：有效的疫苗、不会随着时间发生重大突变的病毒、成功的儿童疫苗接种。

美国疾病预防与控制中心（CDC）数据显示，麻疹疫苗的预防效果为 97％，且研究证实一旦接种疫苗，保护力几乎可以维持一辈子。然而，这三点却无法对应到 COVID-19 疫情上。

　　福奇表示，首先，新冠病毒很大程度地发生突变，2 年多以来已经出现 Alpha、Beta、Delta、Omicron，现在则是 Omicron 亚变种 BA.2。

　　第二个因素是接种人数不够多。伦敦卫生与热带医学院流行病学博士库查斯基（Adam Kucharski）曾估计，以 Delta 病毒的传染力而言，如果疫苗的预防效果为 85％，那么接种率需要达到 98％ 才能达到群体免疫。

　　然而，麻疹疫苗具有绝对的消除性免疫力，可以防止人体再将病毒传播给其他人，但新冠疫苗只能降低传染给他人的几率，接触者仍有可能被感染。

　　福奇提出的最后一点则是免疫缺乏持久性等其他因素，“不仅疫苗引发的免疫不是终身的，就连感染新冠后的免疫也只能维持一段时间。”他表示，这代表人类需要反复接种疫苗或感染，才能让防御力跟上病毒的步伐。

　　尽管如此，有部分学者仍未放弃“群体免疫”的想法。哈佛大学公共卫生名誉教授布鲁姆（Barry Bloom）认为，实现群体免疫的最佳方法就是制造更好的疫苗，目前部分公司正在针对新冠病毒较稳定不变的区域研发疫苗，可能会创造更持久的免疫力，以对抗变种病毒。又或者，病毒的突变可能朝更具传染力，但不一定会导致严重疾病的倾向发展，如同一般感冒的病毒感染。

这里是英文：

Herd immunity is a topic that has come up a lot as a possible way to end the COVID-19 pandemic. And, while numbers have been thrown around in the past about what portion of the population needs to be vaccinated or infected to achieve herd immunity, top public health officials say it’s just unlikely to happen at this point.

In a new article published in the Journal of Infectious Diseases, Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases (NIAID) and other NIAID scientists write that “classical” herd immunity for COVID-19 “almost certainly is an unattainable goal." Dr. Fauci and his co-authors specifically cite “significant obstacles” like “substantial resistance to efforts to control the spread” of SARS-CoV-2, the virus that causes COVID-19, like the public’s resistance to vaccination and mask-wearing.

They also note that “neither infection nor vaccination appears to induce prolonged protection against SARS-CoV-2 in many or most people,” making it tricky to fully prevent COVID-19, even if you’ve been vaccinated or infected with the virus in the past.

But what is herd immunity, exactly, and why is it so tricky to achieve with COVID-19? Here’s what you need to know.

What is herd immunity?

Herd immunity, aka population immunity or community immunity, is what happens when a significant portion of a population develops immunity to an infectious disease, according to the Centers for Disease Control and Prevention (CDC). That can happen through vaccination or a prior infection with a particular illness, the CDC says.

Once herd immunity in a population is achieved, it’s unlikely that an infectious disease will spread from person to person. Herd immunity also offers protection for people who aren’t vaccinated, like newborns, because the disease can’t easily spread in a community, the CDC explains.

Herd immunity is tricky with Omicron, Delta, and other variants

Dr. Fauci and his co-authors pointed out that SARS-CoV-2 keeps developing variants, and that makes it hard to develop herd immunity against it. “This is a mutating virus—we get new subvariants all the time,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “It’s very hard to get sufficient population immunity where that transmission of the virus is completely interrupted.”