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国际疫苗 及时一针

经济学人 3月26日

与非洲贫困地区相比,部分西方国家的疫苗接种率更低。反疫苗者并非罪魁祸首。

消灭疾病是发达国家提出的目标,落后的国家则要很努力才能实现这一目标。但对于一些需要接种疫苗而疫苗存在安全隐患的疾病来说,上述模式正好相反。许多落后国家实施高效疫苗接种方案。传染病致死的记忆虽然离富裕国家逐渐远去,但在世界的某些角落,这些传染病正卷土重来。

据世界卫生组织估计,疫苗每年能挽救约250万人的生命。在疫苗的作用下,1980年,天花得以消灭;不久小儿麻痹症也会被根除。上述两个案例中,发达国家起了示范作用。然而,新的情况看起来与此不同。

这种新趋势在传染性极高的麻疹中体现最为明显。为阻止它的传播,至少95%的人必须接种麻疹疫苗(95%为群体免疫力的一个已知阈值)。尽管疫苗通常是温和的,20但它仍可能导致肺炎、脑损伤和失明等后遗症。疫苗接种率最低的国家都很贫穷,但是许多发展中国家却实施良好的疫苗接种方案(见下图)。其中,厄立特里亚国,卢旺达和斯里兰卡设法让每个人接种疫苗。与之相对的是,包括美国、英国、法国、意大利在内的发达国家低于群体免疫力的阈值。

2015年,欧洲不仅没有实现自己制定的在2010年消灭麻疹这一目标,相反还出现了近4000例麻疹病例。2000年,美国宣布根除麻疹;直到2014年,全美27个州仍然有数以百计的麻疹病例涌现,且2015年出现了近十年来首例麻疹死亡事件。其它一些可通过注射疫苗预防的疾病的趋势令人惊恐,例如风疹(若孕妇患上风疹,可导致新生儿患先天性疾病)等。

人们通常将这一窘境归咎于强硬的“反疫苗者”,即拒不让孩子接种任何疫苗的家长,例如,美国的蒙诺教派排斥现代医学,以及几乎自17世纪以来的所有发明物;部分素食主义者反对疫苗制作中使用动物制品;新教荷兰归正教会则认为疫苗阻止了神的旨意;奥地利神秘主义者兼哲学家鲁道夫・斯坦纳于19世纪提出了人智说,鼓吹疾病可以促进孩子的身体及智力发育。

在大多数国家,仅有2%-3%的家长是上述提及的反疫苗者。然而,因为他们大多为群居生活,这可能使得他们成为疾病爆发的源头。一个更大的问题是,越来越多的父母推迟接种或者选择性接种疫苗。来自美国,澳大利亚和欧洲的研究结果表明,约四分之一的父母已经加入这个阵营,通常是由于他们认为接种疫苗的安排(为了防止十几种疾病而不断的注射疫苗)会导致孩子的免疫系统“超负荷”,或者一些特殊疫苗不够安全。一些人认为疫苗干预了“自然免疫力”。许多人曾被一个说法所动摇,该说法声称麻疹、腮腺炎、风疹三联疫苗(MMR疫苗)会导致自闭症――这一说法后遭拆穿。

在美国,尽管联邦政府提供免费接种疫苗,一些贫穷的孩子还是没能及时注射,因为他们难以跟家庭医生保持定期联系。东欧的某些疾病爆发于罗马(吉普赛人)的社区,这些贫穷、被放逐的少数民族得不到医务人员的关注,他们通常没有接种疫苗。

Some Western countries have lower vaccination rates than poor parts of Africa. Anti-vaxxers are not the main culprits.

ERADICATING a disease is the sort of aim that rich countries come up with, and poor ones struggle to reach. But for some diseases, the pattern is reversed. These are the ailments for which vaccinations exist. Many poor countries run highly effective vaccination programmes. But as memories of the toll from infectious diseases fades across the rich world, in some places they are making a comeback.

The World Health Organisation (WHO) reckons that vaccines save 2.5m lives a year. Smallpox was eradicated in 1980 with the help of a vaccine; polio should soon follow. In both cases, rich countries led the way. The new pattern looks very different.

The trend is most evident for measles, which is highly contagious. At least 95% of people must be vaccinated to stop its spread (a threshold known as “herd immunity”). Although usually mild, it can lead to pneumonia and cause brain damage or blindness. The countries with the lowest vaccination rates are all very poor, but many developing countries run excellent programmes (see chart). Eritrea, Rwanda and Sri Lanka manage to vaccinate nearly everyone. By contrast several rich countries, including America, Britain, France and Italy, are below herd immunity.

Last year Europe missed the deadline it had set itself in 2010 to eradicate measles, and had almost 4,000 cases. America was declared measles-free in 2000; in 2014 it had hundreds of cases across 27 states and last year saw its first death from the disease in more than a decade. The trends for other vaccine-preventable diseases, such as rubella, which can cause congenital disabilities if a pregnant woman catches it, are alarming, too.

This sorry state of affairs is often blamed on hardline “anti-vaxxers”, parents who refuse all vaccines for their children. They are a motley lot. The Amish in America spurn modern medicine, along with almost everything else invented since the 17th century. Some vegans object to the use of animal-derived products in vaccines'manufacture. The Protestant Dutch Reformed Church thinks vaccines thwart divine will. Anthroposophy, founded in the 19th century by Rudolf Steiner, an Austrian mystic-cum-philosopher, preaches that diseases strengthen children’s physical and mental development.

In most countries such refuseniks are only 2-3% of parents. But because they tend to live in clusters, they can be the source of outbreaks. A bigger problem, though, is the growing number of parents who delay vaccination, or pick and choose jabs. Studies from America, Australia and Europe suggest that about a quarter of parents fall into this group, generally because they think that the standard vaccination schedule, which protects against around a dozen diseases, “overloads” children’s immune systems, or that particular vaccines are unsafe. Some believe vaccines interfere with “natural immunity”. Many were shaken by a claim, later debunked, that there was a link between autism and the MMR vaccine, which protects against measles, mumps and rubella.

In America, some poor children miss out on vaccines despite a federal programme to provide the jabs free, since they have no regular relationship with a family doctor. Some outbreaks in eastern Europe have started in communities of Roma (gypsies). Members of this poor and ostracised minority are shunned by health workers and often go unvaccinated.