关于疫苗的七个误区

俞月圆

Few health care topics elicit stronger opinions than pediatric vaccines.

Vaccine advocates see the choice not to immunize children against potentially life-threatening illnesses as a fear-versus-fact， emotion-versus-evidence argument fueled by nonscientific misinformation.

Smaller but seemingly louder groups—known as “anti-vaxxers”—counter by decrying the safety and effectiveness of vaccines and questioning the motives of those who advocate vaccination.

Rush University Medical Center pediatric specialists speak daily with parents who express their fears and beliefs about vaccines. We asked two Rush experts to comment on seven reasons parents often give for not vaccinating their kids.

Myth： Vaccines cause autism.

Fact： “Theres no relationship between any vaccine and autism，” says Renee Slade， MD， a pediatrician in the Rush Pediatric Primary Care Center.

The widespread fear that vaccines increase the risk of autism originated from a 1997 study whose author has since lost his medical license. “After the study was published， it came out that the main author had a financial incentive for the study to be published，” Slade says. “After more was learned about the study， the other authors removed their names. That study has also been debunked by many other studies that used larger groups of children.” The causes of autism and autism spectrum disorders1 have never been established. But many autism experts are increasingly convinced that autism is determined before birth—well before any vaccinations.

Myth： Its not necessary to vaccinate so early in life.

Fact： “The diseases these vaccines prevent are most deadly in the very young，” says pediatric infectious disease specialist Kenneth Boyer， MD. “Thats why they are recommended at the earliest ages.”

Delaying vaccines until children are older simply puts infants and toddlers at greater risk for potentially life-threatening diseases such as whooping cough， measles and diphtheria. Many parents of children under the age of 2 also question whether the increased number of recommended vaccines exposes their young kids to too many antigens—the substances in vaccines that cause the body to build resistance. While there are more vaccines given today than a few decades ago—more than 30 during a childs first six years—the vaccines themselves are more efficient. In the 1980s， the recommended immunization schedule had 3，000 antigens. “Today， we have just 35 antigens， anywhere from 1 to 13 per shot，” says Boyer.

Myth： The vaccine schedule is too aggressive and should be spaced out.

Fact： The immunization schedule is determined by decades of medical evidence showing theres an optimal window of time when vaccines are most effective in preventing—and children are most vulnerable to—these diseases.

However， many parents feel the CDC2s recommended schedule is too aggressive. So they ask their pediatricians to deliver one vaccine at a time， and at a much slower pace. Beyond missing that window of effectiveness， Boyer notes that spacing out immunizations results in more office visits， more injections and， as a result， higher out-of-pocket expenses3.

Myth： Vaccinations cause the diseases that they are meant to prevent.

Fact： Vaccines dont cause diseases， and heres why： They dont contain active viruses.

Vaccines are also known as immunizations because they stimulate our immune systems to produce the antibodies needed to protect us from—or become immune to—diseases. The inactive viruses in vaccines essentially trick the immune system into thinking theres a threat so it will churn out4 those protective antibodies. “Simply put， vaccines ‘mimic the diseases they prevent，” Boyer says. “This induces an immunity that is both natural and long-lasting.” The process of producing antibodies can sometimes cause a low fever or minor swelling， but not the actual diseases.

Myth： Vaccines contain unsafe toxins.

Fact： Its true that vaccines do contain trace amounts of formaldehyde， mercury and aluminum.

But while the names may be scary， these additives actually make the vaccines safer. “They ensure that the vaccine is sterile， or that its able to do its job effectively，” Boyer explains. “They are only toxic in amounts far higher than the trace amounts needed for vaccines.” In fact， formaldehyde is produced at higher rates by the bodys own metabolic system. One mercury-based preservative in particular—Thimerosal—seems to cause the most concern among parents. But since it was eliminated from all pediatric vaccines in 1999， any concerns about Thimerosal today are unfounded.

Myth： The effectiveness of vaccinations has never been proven.

Fact： Simply stated—and scientifically proven—vaccines are extremely effective.

Depending on the vaccine， Slade says， 95 to nearly 100 percent of children will develop immunity against the targeted disease.

Countless scientific studies proving the effectiveness of vaccines can be found on websites like the Centers for Disease Control and Prevention or the American Academy of Pediatrics. But perhaps the most compelling proof that vaccines work is history. “The number of cases for every vaccine-preventable disease plummets in the years after a vaccine for that disease is made widely available，” Slade explains. For instance， the measles vaccine was licensed in the U.S. in 1963. Between 1958 and 1962， more than 503，000 reported measles cases and 432 measles-associated deaths were reported. In 1965， both incidence and deaths began a 33-year downward trend， with record lows of 89 reported cases and zero deaths in 1998.

Myth： Not vaccinating my child affects only my child.

Fact： Unfortunately， as weve seen in recent years， this simply isnt true.

Ironically， some parents skip vaccinations because vaccines have been so effective in making diseases that once killed thousands of children each year quite rare today. But Boyer and other experts point to recent measles and mumps outbreaks to illustrate the concept of “herd immunity.”

Herd—or community—immunity means having a high enough percentage of people in a population （or herd） who are immune from a disease that there are few susceptible people left to infect. Therefore， its very difficult for a disease to spread. But these recent outbreaks show that when a population dips below that amount of vaccinated people needed to prevent an illness from spreading， a disease that was nearly eradicated can resurface with a vengeance—spreading quickly and threatening many lives.

“Not getting vaccinated is like failing to stop at a four-way intersection，” Boyer says. “If three people stop and one doesnt， the risk of an accident is relatively small. If two or three people dont stop， the risk is much higher to everyone at the intersection.”

在醫疗保健领域，没有几个话题比小儿疫苗接种更能引发激烈讨论。

疫苗的支持者认为，不给儿童接种预防可致命疾病的疫苗，是受了不科学的虚假消息的影响，是因为恐惧而忽视了事实、选择情感而舍弃了证据。

反对者人数较少但声势更大，这些人被称为“反疫苗者”。他们谴责疫苗不够安全也不够有效，质疑疫苗接种支持者背后的动机。

拉什大学医学中心的儿科专家每天都会接触到对疫苗心怀恐惧和抱有误解的家长。不让孩子接种疫苗的家长常常给出以下七条理由，我们请拉什大学医学中心的两位专家逐一点评。

错误观点：接种疫苗会导致孤独症。

事实：“任何疫苗都和孤独症毫不相干。”医学博士勒妮·斯莱德说。她是拉什儿童初级医疗中心的一名儿科医生。

人们对于疫苗会提高罹患孤独症风险的普遍担心源自1997年的一项研究报告，但该报告的作者在文章发表后被吊销了行医执照。“该研究报告发表后，人们发现第一作者这么做是受到了经济利益的驱动。”斯莱德说，“该研究的更多情况被曝光后，其他作者纷纷撤掉了自己的名字。许多以更多儿童为样本的研究也驳斥了该研究的结果。”孤独症和孤独症谱系障碍的诱因尚未明确，但越来越多的孤独症专家相信，孤独症是先天决定的，跟出生后接种任何疫苗都毫无关系。

错误观点：没有必要在那么小的时候接种疫苗。

事实：“这些疫苗所预防的疾病对年幼的孩子最为致命，”医学博士、小儿传染病专家肯尼思·博耶说，“所以才推荐在婴幼儿时期接种。”

拖到孩子大一些之后再接种，只会使婴幼儿有更大的风险染上可能致命的疾病，如百日咳、麻疹和白喉。许多子女不满2岁的家长还提出了这样的疑问：推荐接种的疫苗越来越多，会不会让小孩接触太多的抗原（疫苗中促使人体产生抵抗力的物质）。与几十年前相比，我们可接种的疫苗种类确实更多了——孩子出生后头6年可以接种的疫苗超过30种，而疫苗自身的效力也更强了。1980年代，推荐接种时间表中的疫苗共含有3000种抗原。“如今只有35种抗原，每一针中可能有1到13种。”博耶说。

错误观点：疫苗接种时间表安排得太紧，应该留出更多的间隔时间。

事实：数十年的医学经验证明，存在一个最理想的时间窗口，可以使疫苗达到最佳的预防效果，而此时也正是儿童最易感染该疾病的时间。接种时间表就是这么制定出来的。

然而，许多家长觉得疾控中心建议的时间表安排得太紧，便要求他们的儿科医生一次只注射一支疫苗，并将接种的进度大大放缓。博耶指出，在疫苗接种之间留出更多间隔时间不仅会错过效果最佳的窗口期，还会增加就诊次数、注射次数，并因此增加自费支出。

错误观点：疫苗会让接种者染上那些计划预防的疾病。

事实：疫苗不会让人染病，原因是它们并不含有活体病毒。

疫苗接种也称为“免疫接种”，因为疫苗可以刺激我们的免疫系统产生抗体，保护我们不受疾病的侵扰（或者说对疾病产生免疫）。疫苗里的灭活病毒实际是让免疫系统误以为存在威胁，于是它会大量生成具有保护作用的抗体。“简单来说，疫苗‘模仿了它们所预防的疾病，”博耶说，“从而引发一种自然而持久的免疫。”产生抗体的过程有时会导致低烧或轻微肿胀，但接种者不会真的患上那种疾病。

错误观点：疫苗含有不安全的有毒成分。

事實：疫苗的确含有微量的甲醛、汞和铝。

这些添加剂的名字可能很可怕，但实际上它们使疫苗变得更安全。“这些成分可以确保疫苗无菌，或者使疫苗效果更好。”博耶解释道，“只有剂量远远超过疫苗中的微量成分时，它们才具有毒性。”其实，人体自身新陈代谢生成的甲醛比疫苗中的甲醛更多。最让家长担心的是一种汞基防腐剂——硫柳汞。但从1999年起，硫柳汞已不再用于任何一种小儿疫苗。如今对于硫柳汞的担忧都是没有根据的。

错误观点：疫苗的有效性从未得到证实。

事实：简单地说，疫苗非常有效。这是经过科学证明的。

斯莱德说，依靠疫苗，95%到近100%的儿童能产生针对某种疾病的免疫力。

在美国疾病控制与预防中心或美国儿科学会等网站上，可以找到不计其数的证明疫苗有效性的科学研究。但也许证明疫苗有效的最强证据是历史。“每一种可以用疫苗预防的疾病的病例数，在针对该疾病的疫苗广泛应用后的若干年里都会迅速下降。”斯莱德解释道。例如，麻疹疫苗于1963年在美国获批。1958年至1962年，共报告超过50.3万例麻疹确诊病例和432例与麻疹相关的死亡病例。自1965年起，麻疹确诊病例数和死亡病例数连续33年下降，1998年达到创纪录的低值：89例确诊，0例死亡。

错误观点：我的孩子不接种，受影响的只是我的孩子。

事实：很不幸，根据我们近年的观察，这种看法是不对的。

讽刺的是，有些家长放弃接种恰恰是因为疫苗效果明显，有些疾病以前每年会导致成千上万儿童死亡，如今已经十分少见。但博耶和其他专家借用近期麻疹和流行性腮腺炎的疫情，解释了“群体免疫”的概念。

“群体免疫”（或称“社区免疫”）指人群（或畜群）中对某种疾病具有免疫力的个体占到足够高的比例，能够染上这种疾病的易感者已经寥寥无几。由此，这种疾病便难以再传播。但近期暴发的几次疫情表明，当人口中疫苗接种人数低于防止疾病传播所需的水平时，一种几乎已被根除的疾病可能猛烈反弹，迅速传播，威胁许多人的生命。

“不接种疫苗就像没能在十字路口停下，”博耶说，“如果三个人停了下来，一个人没停住，发生交通事故的风险相对比较小。如果两个人或者三个人没有停下来，那对身处路口的每个人来说，风险都会大大增加。”

（译者为“《英语世界》杯”翻译大赛获奖者）