美國在2000年宣布麻疹已經在當地得到了根治。去年一年，美國27個州確診了644例麻疹，創下美國2000年宣布已消滅麻疹疫情以來的新高。今年可能也不會好轉，據美國疾病控製與預防中心統計，至本月2日已經有14個州報告了102個病例。

        該中心主任弗裏登1日警告稱，“美國可能會暴發一場大規模的麻疹疫情”。弗裏登表示，已經采取強有力的公共衛生措施來甄別患者，但防止麻疹擴散最有效的方法是接種疫苗。弗裏登稱，很多家長沒有給孩子接種疫苗，有些人擔心疫苗的安全性，有些人則認為麻疹已經不存在了。

        根據CDC統計，麻疹疫苗對於疾病的預防比例為93-97%。麻疹是由麻疹病毒引起的，一種高度傳染性呼吸道疾病，其症狀包括發熱、咳嗽、皮膚出現紅色斑丘疹等，嚴重者可引發肺炎。

        病毒的常見並發症包括耳部感染和腹瀉，而更嚴重的並發症包括肺炎(兒童中麻疹相關性死亡最常見原因)，腦炎(可引起抽搐，耳聾和腦損傷)。

        在1912年，麻疹首次成為“全國法定報告”(麻疹首次成為“全國法定報告疾病”)性疾病，醫療保健提供者必須報告所有確診病例。在接下來的10年中，每年大約有6000例麻疹相關死亡事件發生。

        在20世紀50年代，在美國每年大約300-400萬人感染麻疹病毒，大約48000人住院， 400-500人死於該病毒。在15歲之前，幾乎所有孩子均感染麻疹，每年大約4000人發展麻疹相關性腦炎。

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.

        麻疹疫苗於20世紀60年代初在美國首次問世，由美國生物醫學科學家John F. Enders和同事共同研發。 1968年，由美國微生物學家Maurice Hilleman和同事共同研發的改進麻疹疫苗在美國廣泛使用，該疫苗已使用至今。

        1971年，麻疹、腮腺炎和風疹的聯合疫苗(MMR疫苗)，或者與腮腺炎、風疹、水痘聯合疫苗(MMRV疫苗)顯著減少了美國麻疹病例的數量。

        1981年之前，該疫苗是單劑量給藥，與上年相比，已經減少了80%的麻疹報告病例數。但在1989-1991暴發了嚴重的麻疹疫情， 55622名美國人可能感染病毒，其中123人死亡。疫情暴發是由於疫苗接種率過低， 90%的死亡發生在沒有接種疫苗的人群中。

        因此，一些醫療機構，包括免疫接種谘詢委員會實踐(ACIP)和美國小兒科學會(AAP) 建議給所有孩子接種兩劑MMR疫苗，而不是一劑。因此兒童疫苗(VFC)計劃在1994年提出。

        現在，美國疾病控製和預防中心(CDC)推薦所有孩子接受兩劑MMR疫苗，第一劑建議在12-15個月齡接種，第二劑量建議在4-6歲接種。

        對麻疹病毒不能免疫的成年人，疾病預防控製中心也建議他們應該至少接種MMR疫苗一劑。

        與“前”疫苗時代相比，CDC稱在美國MMR疫苗減少了99%的麻疹病例，而在2000年宣布麻疹已經在當地得到了根治。這意味著當年超過12個月沒有連續疾病傳播。

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.

        在美國總會有麻疹病例產生，因為可以從別的國家沒有接種過疫苗的人群帶入國內。但在2000年至2007年，麻疹病例數量達到曆史紀錄低點，在2004年報告的隻有37例病例。

        然而近年來，在美國麻疹病例人數持續上升。在2008年，年病例報告數超過了自2001年以來的首個100例大關。在2011年，年病例報告數超過了200例。

        去年一年，美國27個州確診了644例麻疹，創下美國2000年宣布已消滅麻疹疫情以來的新高。

        美國疾病控製和預防中心說稱，大部分患者是被來美國旅遊的菲律賓旅客感染– 時值當地麻疹疫情大暴發- 在美國大多數感染人群都是部分未接種疫苗的俄亥俄州亞米希人(Amish)。衛生官員說，亞米希傳教士從菲律賓回到美國之後，疫情爆發。菲律賓正在經曆麻疹疫情大爆發，全國已經報告2.6萬病例。

        雖然去年的數據不容樂觀，但是今年的數據依然不佳。據美疾控中心發布的統計數字，今年1月1日至30日，美國加利福尼亞州和紐約州等14個州出現麻疹疫情，共有102人感染，這些病例中有許多人曾到加州的迪士尼樂園遊玩。加州迪士尼樂園去年12月出現麻疹疫情，但其源頭尚無法確定。

        在上月月底的新聞發布會上， CDC免疫和呼吸係統疾病預控中心主任Anne Schuchat博士說，今年的麻疹疫情暴發應當引起足夠的關注。

        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.

        在美國麻疹疫苗接種率整體比較好， 2013年CDC報告顯示，年齡在19-35個月的兒童MMR疫苗接種率為91.9% ，但是各地區接種率差異還是很顯著的。

        例如最近麻疹疫情暴發科羅拉多州， MMR疫苗接種率隻有82%，CDC2013年報告顯示，美國有17個州的MMR疫苗接種率在90%以下。

        一份疾病預防控製中心的報告顯示，因為個人的原因，去年的麻疹病例中79%患者沒有選擇接種MMR疫苗。 盡管CDC表示MMR疫苗是安全的，單劑量疫苗的有效率約93%，而兩次劑量有效率約97%，但是為什麼還有很多人沒有給自己或孩子接種疫苗呢?

        首先，疫苗接種率下降是因為宗教或個人原因。大眾擔心這種疫苗對於兒童是不安全的。

        這種觀念來源1998年的一項研究，英國權威醫學雜誌《柳葉刀》發表醫生韋克菲爾德的論文，稱麻腮風三聯疫苗可能引發自閉症，經媒體報道後，不少家長拒絕為孩子接種該疫苗。雖然其他研究無法重現該結果，但該研究對疫苗接種影響顯著。英國此次麻疹暴發的起源應該追溯至此，6年後的2004年，英國三聯疫苗接種率由最高時期的92%降至81%。

        韋克菲爾德的論文發表後，不少醫學研究人員紛紛撰文批駁。英國醫學研究委員會等機構隨後也開展了長期研究，最終未發現這款疫苗與自閉症存在關聯。2010年，英國醫學總會吊銷了韋克菲爾德的行醫資格，《柳葉刀》也撤下了相關論文。

       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.

        約翰霍普金斯大學醫學院生物醫學工程，計算機科學和生物統計學教授Steven Salzberg說，最新麻疹疫情的發生是因為沒有接種疫苗的人群越來越多造成的。

        他補充道，反對兒童接種疫苗的運動是錯誤的，盡管有充足的科學證據表明疫苗是有效的，但是他們無休止地重複了各種錯誤的聲明，如疫苗引發自閉症。”

        他繼續補充道，在過去的15年裏，數十個涉及數百萬人的研究充分證明疫苗的任何成分都與自閉症無關，疫苗不僅安全，也許是人類文明史中最偉大的公共衛生成就。

        教授和Schuchat博士均指出，我們不應低估麻疹的嚴重性。1/10的小兒感染麻疹後發生耳部感染，這可能導致聽力喪失，約1/20發展為肺炎。在此麻疹疫情暴發之際，一季度1/4的感染者已被送往醫院。

        博士在新聞發布會上說，今年的新聞應答發出警告，麻疹仍在進入美國，未接種疫苗人群可能會感染病毒。

        因此，全國疾病預防控製中心和衛生保健專業人士呼籲所有人確保他們接種過麻疹疫苗。Schuchat博士說，許多人認為麻疹消失了，且自己和子女均沒有接種疫苗的家長應引起警惕，麻疹疫情仍在蔓延，甚至可能會越發嚴重。MMR疫苗是安全有效的，高度推薦使用。

        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."