美国在2000年宣布麻疹已经在当地得到了根治。去年一年，美国27个州确诊了644例麻疹，创下美国2000年宣布已消灭麻疹疫情以来的新高。今年可能也不会好转，据美国疾病控制与预防中心统计，至本月2日已经有14个州报告了102个病例。

        该中心主任弗里登1日警告称，“美国可能会暴发一场大规模的麻疹疫情”。弗里登表示，已经采取强有力的公共卫生措施来甄别患者，但防止麻疹扩散最有效的方法是接种疫苗。弗里登称，很多家长没有给孩子接种疫苗，有些人担心疫苗的安全性，有些人则认为麻疹已经不存在了。

        根据CDC统计，麻疹疫苗对于疾病的预防比例为93-97%。麻疹是由麻疹病毒引起的，一种高度传染性呼吸道疾病，其症状包括发热、咳嗽、皮肤出现红色斑丘疹等，严重者可引发肺炎。

        病毒的常见并发症包括耳部感染和腹泻，而更严重的并发症包括肺炎(儿童中麻疹相关性死亡最常见原因)，脑炎(可引起抽搐，耳聋和脑损伤)。

        在1912年，麻疹首次成为“全国法定报告”(麻疹首次成为“全国法定报告疾病”)性疾病，医疗保健提供者必须报告所有确诊病例。在接下来的10年中，每年大约有6000例麻疹相关死亡事件发生。

        在20世纪50年代，在美国每年大约300-400万人感染麻疹病毒，大约48000人住院， 400-500人死于该病毒。在15岁之前，几乎所有孩子均感染麻疹，每年大约4000人发展麻疹相关性脑炎。

Are ongoing concerns about vaccine safety to blame for the measles epidemic?

        In 2000, measles was declared eliminated in the US. But last year saw a record number of measles cases since - 644 over 27 US states. This year is unlikely to be any better, with 102 cases reported so far. In this spotlight, we look at whether ongoing concerns surrounding vaccination safety are behind the measles epidemic.

        According to the CDC, the MMR vaccine is 93-97% effective at preventing measles.Measles is a highly contagious respiratory disease caused by infection with the morbillivirus. Onset of the disease usually begins with a fever, cough, inflamed eyes, runny nose and sore throat, before a red, blotchy rash appears all over the body.

        Common complications of the virus include ear infections and diarrhea, while more severe complications include pneumonia - the most common cause of measles-related death in children, and swelling of the brain, known as encephalitis, which can cause convulsions, deafness and brain damage.

        Measles first became a "nationally notifiable" disease - a condition in which health care providers had to report all diagnosed cases - in the US in 1912. Over the following decade, there were around 6,000 measles-related deaths in the country each year.

        In the 1950s, around 3-4 million people in the US became infected with measles annually, with around 48,000 hospitalizations and 400-500 deaths from the virus each year. Almost all children contracted measles by the age of 15, and around 4,000 people developed measles-related encephalitis each year.

        麻疹疫苗于20世纪60年代初在美国首次问世，由美国生物医学科学家John F. Enders和同事共同研发。 1968年，由美国微生物学家Maurice Hilleman和同事共同研发的改进麻疹疫苗在美国广泛使用，该疫苗已使用至今。

        1971年，麻疹、腮腺炎和风疹的联合疫苗(MMR疫苗)，或者与腮腺炎、风疹、水痘联合疫苗(MMRV疫苗)显著减少了美国麻疹病例的数量。

        1981年之前，该疫苗是单剂量给药，与上年相比，已经减少了80%的麻疹报告病例数。但在1989-1991暴发了严重的麻疹疫情， 55622名美国人可能感染病毒，其中123人死亡。疫情暴发是由于疫苗接种率过低， 90%的死亡发生在没有接种疫苗的人群中。

        因此，一些医疗机构，包括免疫接种咨询委员会实践(ACIP)和美国小儿科学会(AAP) 建议给所有孩子接种两剂MMR疫苗，而不是一剂。因此儿童疫苗(VFC)计划在1994年提出。

        现在，美国疾病控制和预防中心(CDC)推荐所有孩子接受两剂MMR疫苗，第一剂建议在12-15个月龄接种，第二剂量建议在4-6岁接种。

        对麻疹病毒不能免疫的成年人，疾病预防控制中心也建议他们应该至少接种MMR疫苗一剂。

        与“前”疫苗时代相比，CDC称在美国MMR疫苗减少了99%的麻疹病例，而在2000年宣布麻疹已经在当地得到了根治。这意味着当年超过12个月没有连续疾病传播。

The rise of the measles vaccine

        But in the early 1960s came the first licensed measles vaccine in the US, created by American biomedical scientist John F. Enders and colleagues. In 1968, an improved measles vaccine - created by American microbiologist Maurice Hilleman and colleagues - was distributed in the US, and this vaccine has been used ever since.

        The vaccine - which in 1971, was administered in combination with mumps and rubella to form the MMR vaccine, or with mumps, rubella and varicella to form the MMRV vaccine - dramatically reduced the the number of measles cases in the US.

        It was first administered in a single dose, which by 1981, had reduced the number of reported measles cases by 80%, compared with the previous year. But in 1989-91 came a severe measles outbreak, which saw 55,622 Americans become infected with the virus and 123 associated deaths. The outbreak was attributed to low vaccination rates; 90% of all fatalities occurred in people who were not vaccinated.

        As a result, a number of health bodies - including the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) - recommended that the MMR vaccine be given to all children in two doses instead of one. This led to the Vaccines for Children (VFC) program being introduced in 1994.

        Now, current recommendations from the Centers for Disease Control and Prevention (CDC) state that all children should receive two doses of the MMR vaccine, with the first dose to be administered at the age of 12-15 months and the second dose to be given at the age of 4-6 years.

        For adults who are not immune to the measles virus, the CDC recommend that they should receive at least one dose of the MMR vaccine.

        Compared with the pre-vaccine era, the CDC say the MMR vaccine has led to a 99% reduction in measles cases in the US, and in 2000, measles was declared eliminated in the country - meaning there had been no continuous disease transmission for over 12 months.

        在美国总会有麻疹病例产生，因为可以从别的国家没有接种过疫苗的人群带入国内。但在2000年至2007年，麻疹病例数量达到历史纪录低点，在2004年报告的只有37例病例。

        然而近年来，在美国麻疹病例人数持续上升。在2008年，年病例报告数超过了自2001年以来的首个100例大关。在2011年，年病例报告数超过了200例。

        去年一年，美国27个州确诊了644例麻疹，创下美国2000年宣布已消灭麻疹疫情以来的新高。

        美国疾病控制和预防中心说称，大部分患者是被来美国旅游的菲律宾旅客感染– 时值当地麻疹疫情大暴发- 在美国大多数感染人群都是部分未接种疫苗的俄亥俄州亚米希人(Amish)。卫生官员说，亚米希传教士从菲律宾回到美国之后，疫情爆发。菲律宾正在经历麻疹疫情大爆发，全国已经报告2.6万病例。

        虽然去年的数据不容乐观，但是今年的数据依然不佳。据美疾控中心发布的统计数字，今年1月1日至30日，美国加利福尼亚州和纽约州等14个州出现麻疹疫情，共有102人感染，这些病例中有许多人曾到加州的迪士尼乐园游玩。加州迪士尼乐园去年12月出现麻疹疫情，但其源头尚无法确定。

        在上月月底的新闻发布会上， CDC免疫和呼吸系统疾病预控中心主任Anne Schuchat博士说，今年的麻疹疫情暴发应当引起足够的关注。

        Recent outbreaks have led to concern

        There will always be some cases of measles in the US, as it can still be brought into the country by individuals from other countries who have not been vaccinated. But between 2000 and 2007, the number of measles cases reached a record low, with only 37 cases being reported in 2004.

        In recent years, however, the number of measles cases in the US has risen. In 2008, the number of annually reported cases passed the 100 mark for the first time since 2001, and in 2011, more than 200 cases were reported.

        But last year saw the highest number of reported measles cases in the US since the virus had been declared eliminated. There were 23 measles outbreaks in 2014, causing 644 people to become infected.

        According to the CDC, the majority of these cases were brought into the country by travelers from the Philippines - where a large outbreak of the virus was occurring at the time - and most of the people who became infected in the US were part of unvaccinated Amish communities in Ohio.

        But while last year's statistics seem bad, this year's are set to be even worse. Last month alone saw 102 measles cases reported over 14 US states, including California, Texas and Washington. The majority of these cases are thought to have stemmed from Disneyland, CA, where a number of people reported developing the virus after visiting the amusement part in mid-December.

        In a press briefing at the end of last month, Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Disease at the CDC, said this year's outbreak is a concern:

        "It's only January and we have already had a very large number of measles cases - as many cases as we have all year in typical years. This worries me and I want to do everything possible to prevent measles from getting a foothold in the United States and becoming endemic again."

        And according to the CDC, vaccination is the key to getting a "foothold" on measles in the US, and it is primarily lack of vaccination that has contributed to the recent outbreaks.

        在美国麻疹疫苗接种率整体比较好， 2013年CDC报告显示，年龄在19-35个月的儿童MMR疫苗接种率为91.9% ，但是各地区接种率差异还是很显著的。

        例如最近麻疹疫情暴发科罗拉多州， MMR疫苗接种率只有82%，CDC2013年报告显示，美国有17个州的MMR疫苗接种率在90%以下。

        一份疾病预防控制中心的报告显示，因为个人的原因，去年的麻疹病例中79%患者没有选择接种MMR疫苗。 尽管CDC表示MMR疫苗是安全的，单剂量疫苗的有效率约93%，而两次剂量有效率约97%，但是为什么还有很多人没有给自己或孩子接种疫苗呢?

        首先，疫苗接种率下降是因为宗教或个人原因。大众担心这种疫苗对于儿童是不安全的。

        这种观念来源1998年的一项研究，英国权威医学杂志《柳叶刀》发表医生韦克菲尔德的论文，称麻腮风三联疫苗可能引发自闭症，经媒体报道后，不少家长拒绝为孩子接种该疫苗。虽然其他研究无法重现该结果，但该研究对疫苗接种影响显著。英国此次麻疹暴发的起源应该追溯至此，6年后的2004年，英国三联疫苗接种率由最高时期的92%降至81%。

        韦克菲尔德的论文发表后，不少医学研究人员纷纷撰文批驳。英国医学研究委员会等机构随后也开展了长期研究，最终未发现这款疫苗与自闭症存在关联。2010年，英国医学总会吊销了韦克菲尔德的行医资格，《柳叶刀》也撤下了相关论文。

       Safety of MMR vaccine is still questioned

        While measles vaccination coverage across the US looks positive overall - with the CDC reporting a 91.9% MMR vaccine coverage among children aged 19-35 months in 2013 - it varies significantly by state.

        For example, Colorado - which has been affected by the latest measles outbreak - only has an MMR vaccine coverage of 82%, and a 2013 report from the CDC revealed that 17 US states have an MMR vaccine coverage below 90%.

        A report from the CDC found that last year, 79% of measles cases occurred among people who opted out of the MMR vaccine due to personal beliefs.The CDC say the MMR vaccine is safe, and one dose of the vaccine is around 93% effective at preventing measles, while two doses is approximately 97% effective. So why are many people still not getting themselves or their children vaccinated?

        Primarily, it is down to religious or personal beliefs. A report from the CDC found that last year, 79% of measles cases occurred among people who opted out of the MMR vaccine due to personal beliefs. And these personal beliefs tend to be associated with worries that the vaccine is unsafe for children.

        This belief stems from a study published in The Lancet in 1998, conducted by British researcher Andrew Wakefield and colleagues from the UK. In this study involving 12 children, Wakefield and his team suggested a link between the MMR vaccine and autism.

        Though other studies were unable to reproduce the findings, Wakefield's research had a significant impact on vaccination coverage. In the UK, MMR vaccination rates fell from 90% to 80%, while measles cases began to rise.

        The study has since been retracted by The Lancet, having been deemed as "fraudulent" after undisclosed financial conflicts of interest were revealed by a journalist called Brian Deer in 2011. As a result, Wakefield lost his medical license. But regardless of this outcome, he stands by his findings, and so do many others.

        One of the most well-known supporters of Wakefield's claim is former Playboy centerfold Jenny McCarthy, whose son developed autism, which she attributes to vaccination. She claims that current vaccines are unsafe and contribute to autism and other disorders.

        "I do believe sadly it's going to take some diseases coming back to realize that we need to change and develop vaccines that are safe," she said in an interview with the Chicago Sun Times last year. "If the vaccine companies are not listening to us, it's their [...] fault that the diseases are coming back. If you give us a safe vaccine, we'll use it."

        Many parents in the US support McCarthy's statement, but the CDC and other health organizations warn that this perception toward vaccination is putting the public's health at risk.

        约翰霍普金斯大学医学院生物医学工程，计算机科学和生物统计学教授Steven Salzberg说，最新麻疹疫情的发生是因为没有接种疫苗的人群越来越多造成的。

        他补充道，反对儿童接种疫苗的运动是错误的，尽管有充足的科学证据表明疫苗是有效的，但是他们无休止地重复了各种错误的声明，如疫苗引发自闭症。”

        他继续补充道，在过去的15年里，数十个涉及数百万人的研究充分证明疫苗的任何成分都与自闭症无关，疫苗不仅安全，也许是人类文明史中最伟大的公共卫生成就。

        教授和Schuchat博士均指出，我们不应低估麻疹的严重性。1/10的小儿感染麻疹后发生耳部感染，这可能导致听力丧失，约1/20发展为肺炎。在此麻疹疫情暴发之际，一季度1/4的感染者已被送往医院。

        博士在新闻发布会上说，今年的新闻应答发出警告，麻疹仍在进入美国，未接种疫苗人群可能会感染病毒。

        因此，全国疾病预防控制中心和卫生保健专业人士呼吁所有人确保他们接种过麻疹疫苗。Schuchat博士说，许多人认为麻疹消失了，且自己和子女均没有接种疫苗的家长应引起警惕，麻疹疫情仍在蔓延，甚至可能会越发严重。MMR疫苗是安全有效的，高度推荐使用。

        MMR vaccine: 'safe, effective and highly recommended

        'Writing in an article for Forbes, Steven Salzberg, a professor of biomedical engineering, computer science and biostatistics at Johns Hopkins University School of Medicine in Baltimore, MD, says this latest measles epidemic has been "fueled by growing enclaves of unvaccinated people."

        "Anti-vaxxers have been relentless in the efforts to spread misinformation," he adds. "Despite overwhelming scientific evidence that vaccines are beneficial, they endlessly repeat a variety false claims, such as vaccines cause autism."

        "Over the past 15 years, dozens of studies involving hundreds of thousands of people have shown convincingly that neither vaccines nor any of the ingredients in them are linked to autism," he continues. "Vaccines are not only safe, but they are perhaps the greatest public health success in the history of civilization."

        Both Prof. Salzburg and Dr. Schuchat note that we should not underestimate how serious measles can be. Around 1 in 10 children with measles develop ear infections, which can lead to hearing loss, and around 1 in 20 develop pneumonia. In this outbreak alone, a quarter of infected individuals have been hospitalized as a result.

        "The news this year is concerning and serves as a warning that measles is still coming into the United States and that unvaccinated people can get exposed," said Dr. Schuchat in a press briefing.

        "These outbreaks the past couple of years have been much harder to control when the virus reaches communities where numbers of people have not been vaccinated and, of course, when the virus comes into the country and exposing people at large venues where many people gather, the chances of exposure are greater," she added.

        As such, the CDC and health care professionals across the country are calling for all individuals to ensure they receive the measles vaccination. Dr. Schuchat said:

        "I want to make sure that parents who think that measles is gone and haven't made sure that they or their children are vaccinated are aware that measles is still around and it can be serious. And that MMR vaccine is safe and effective and highly recommended."

        Whether Dr. Schuchat's reassurance that the MMR vaccine is safe will encourage increased vaccination coverage going forward is unclear. But Prof. Salzburg says it is possible the measles epidemic itself will change people's views about vaccination.

        "Perhaps the Disneyland epidemic will finally convince parents, schools, and state legislatures that they need to insist that children get vaccinated before going to school," he wrote in Forbes. "Perhaps it will also convince parents to stop listening to nonsense, and choose wisely by getting their children vaccinated against measles. We won this battle before, and we can win it again."