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        The study has since been retracted by The Lancet, having been deemed as "fraudulent" after undisclosed financial conflicts of interest were revealed by a journalist called Brian Deer in 2011.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.