關于疫苗的七個誤區

俞月圓

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.”

在醫療保健領域，沒有幾個話題比小兒疫苗接種更能引發激烈討論。

疫苗的支持者認為，不給兒童接種預防可致命疾病的疫苗，是受了不科學的虛假消息的影響，是因為恐懼而忽視了事實、選擇情感而舍棄了證據。

反對者人數較少但聲勢更大，這些人被稱為“反疫苗者”。他們譴責疫苗不夠安全也不夠有效，質疑疫苗接種支持者背后的動機。

拉什大學醫學中心的兒科專家每天都會接觸到對疫苗心懷恐懼和抱有誤解的家長。不讓孩子接種疫苗的家長常常給出以下七條理由，我們請拉什大學醫學中心的兩位專家逐一點評。

錯誤觀點：接種疫苗會導致孤獨癥。

事實：“任何疫苗都和孤獨癥毫不相干。”醫學博士勒妮·斯萊德說。她是拉什兒童初級醫療中心的一名兒科醫生。

人們對于疫苗會提高罹患孤獨癥風險的普遍擔心源自1997年的一項研究報告，但該報告的作者在文章發表后被吊銷了行醫執照。“該研究報告發表后，人們發現第一作者這么做是受到了經濟利益的驅動。”斯萊德說，“該研究的更多情況被曝光后，其他作者紛紛撤掉了自己的名字。許多以更多兒童為樣本的研究也駁斥了該研究的結果。”孤獨癥和孤獨癥譜系障礙的誘因尚未明確，但越來越多的孤獨癥專家相信，孤獨癥是先天決定的，跟出生后接種任何疫苗都毫無關系。

錯誤觀點：沒有必要在那么小的時候接種疫苗。

事實：“這些疫苗所預防的疾病對年幼的孩子最為致命，”醫學博士、小兒傳染病專家肯尼思·博耶說，“所以才推薦在嬰幼兒時期接種。”

拖到孩子大一些之后再接種，只會使嬰幼兒有更大的風險染上可能致命的疾病，如百日咳、麻疹和白喉。許多子女不滿2歲的家長還提出了這樣的疑問：推薦接種的疫苗越來越多，會不會讓小孩接觸太多的抗原（疫苗中促使人體產生抵抗力的物質）。與幾十年前相比，我們可接種的疫苗種類確實更多了——孩子出生后頭6年可以接種的疫苗超過30種，而疫苗自身的效力也更強了。1980年代，推薦接種時間表中的疫苗共含有3000種抗原。“如今只有35種抗原，每一針中可能有1到13種。”博耶說。

錯誤觀點：疫苗接種時間表安排得太緊，應該留出更多的間隔時間。

事實：數十年的醫學經驗證明，存在一個最理想的時間窗口，可以使疫苗達到最佳的預防效果，而此時也正是兒童最易感染該疾病的時間。接種時間表就是這么制定出來的。

然而，許多家長覺得疾控中心建議的時間表安排得太緊，便要求他們的兒科醫生一次只注射一支疫苗，并將接種的進度大大放緩。博耶指出，在疫苗接種之間留出更多間隔時間不僅會錯過效果最佳的窗口期，還會增加就診次數、注射次數，并因此增加自費支出。

錯誤觀點：疫苗會讓接種者染上那些計劃預防的疾病。

事實：疫苗不會讓人染病，原因是它們并不含有活體病毒。

疫苗接種也稱為“免疫接種”，因為疫苗可以刺激我們的免疫系統產生抗體，保護我們不受疾病的侵擾（或者說對疾病產生免疫）。疫苗里的滅活病毒實際是讓免疫系統誤以為存在威脅，于是它會大量生成具有保護作用的抗體。“簡單來說，疫苗‘模仿了它們所預防的疾病，”博耶說，“從而引發一種自然而持久的免疫。”產生抗體的過程有時會導致低燒或輕微腫脹，但接種者不會真的患上那種疾病。

錯誤觀點：疫苗含有不安全的有毒成分。

事實：疫苗的確含有微量的甲醛、汞和鋁。

這些添加劑的名字可能很可怕，但實際上它們使疫苗變得更安全。“這些成分可以確保疫苗無菌，或者使疫苗效果更好。”博耶解釋道，“只有劑量遠遠超過疫苗中的微量成分時，它們才具有毒性。”其實，人體自身新陳代謝生成的甲醛比疫苗中的甲醛更多。最讓家長擔心的是一種汞基防腐劑——硫柳汞。但從1999年起，硫柳汞已不再用于任何一種小兒疫苗。如今對于硫柳汞的擔憂都是沒有根據的。

錯誤觀點：疫苗的有效性從未得到證實。

事實：簡單地說，疫苗非常有效。這是經過科學證明的。

斯萊德說，依靠疫苗，95%到近100%的兒童能產生針對某種疾病的免疫力。

在美國疾病控制與預防中心或美國兒科學會等網站上，可以找到不計其數的證明疫苗有效性的科學研究。但也許證明疫苗有效的最強證據是歷史。“每一種可以用疫苗預防的疾病的病例數，在針對該疾病的疫苗廣泛應用后的若干年里都會迅速下降。”斯萊德解釋道。例如，麻疹疫苗于1963年在美國獲批。1958年至1962年，共報告超過50.3萬例麻疹確診病例和432例與麻疹相關的死亡病例。自1965年起，麻疹確診病例數和死亡病例數連續33年下降，1998年達到創紀錄的低值：89例確診，0例死亡。

錯誤觀點：我的孩子不接種，受影響的只是我的孩子。

事實：很不幸，根據我們近年的觀察，這種看法是不對的。

諷刺的是，有些家長放棄接種恰恰是因為疫苗效果明顯，有些疾病以前每年會導致成千上萬兒童死亡，如今已經十分少見。但博耶和其他專家借用近期麻疹和流行性腮腺炎的疫情，解釋了“群體免疫”的概念。

“群體免疫”（或稱“社區免疫”）指人群（或畜群）中對某種疾病具有免疫力的個體占到足夠高的比例，能夠染上這種疾病的易感者已經寥寥無幾。由此，這種疾病便難以再傳播。但近期暴發的幾次疫情表明，當人口中疫苗接種人數低于防止疾病傳播所需的水平時，一種幾乎已被根除的疾病可能猛烈反彈，迅速傳播，威脅許多人的生命。

“不接種疫苗就像沒能在十字路口停下，”博耶說，“如果三個人停了下來，一個人沒停住，發生交通事故的風險相對比較小。如果兩個人或者三個人沒有停下來，那對身處路口的每個人來說，風險都會大大增加。”

（譯者為“《英語世界》杯”翻譯大賽獲獎者）