在新冠肺炎的担忧促使美国对来自包括巴西在内的国家的国际旅客关闭边境一年半之后，中国印度，南非，美国联合王国和欧洲大部分地区一样，限制正在转向关注疫苗状况。

从周一开始，来自特定国家的旅行禁令已经结束。美国将允许国际旅客入境，但他们必须接种疫苗——只有少数例外。

美国还将重新开放与加拿大和墨西哥的陆地边界，让接种疫苗的人入境。从加拿大和墨西哥到美国的大多数旅行都是通过陆路而不是航空。

以下是关于这些变化的一些问题和答案:

为什么会发生这些变化?

政府表示，目标是在限制新冠肺炎疫情蔓延的同时，恢复更多的正常出行。旅游业和欧洲盟友已经推动结束针对特定国家的禁令。几个月来，美国人被允许飞往欧洲，欧洲人一直在敦促美国改变政策。

2019年，在大流行之前，大约7900万美国游客中，约有五分之一来自欧洲。

主要要求是什么?

所有前往美国的成年外国公民在登机前都必须全面接种疫苗。和以前一样，旅客仍需出示出发去美国后72小时内新冠肺炎检测呈阴性的证明

每个人都需要接种疫苗?

是的，除了一些例外。18岁以下的儿童不需要接种疫苗，但他们需要进行COVID测试。2岁及以下的孩子免于测试要求。

没有接种疫苗的成年人怎么办?

由于世界上有一半的人口仍未接种疫苗，而且疫苗的分发过于偏向富裕国家，拜登政府正在给那些生活在疫苗很稀少。这份名单包括大约50个国家，只有不到10%的人接种过疫苗。来自这些国家的旅行者需要美国政府的许可才能来，而且不能只是为了旅游或商务旅行。

美国政府表示，如果有人道主义或紧急原因，如紧急医疗后送，将允许未接种疫苗的国际游客入境。这些例外将“极其狭隘地”适用，并需要疾病控制和预防中心的批准。也有可能是医学上的例外，有医生的证明文件。

美国人将不得不做什么?

未接种疫苗的美国人必须在国际旅行的一天内出示新冠肺炎检测呈阴性的证明。如果你接种了疫苗，无论是美国人还是其他国家的公民，你都需要在出发后的三天内进行检测。这不适用于美国境内的航班

谁将执行疫苗规则?

这取决于航空公司。他们将必须核实疫苗记录，并将其与身份证进行匹配，如果他们不这样做，他们可能面临每次违规高达近3.5万美元的罚款。航空公司还将收集乘客的信息，用于联系追踪工作。在美国，疾控中心的工作人员将抽查旅行者是否符合规定

哪些疫苗会让你接种?

大部分但不是全部。世界卫生组织批准紧急使用的任何新冠肺炎疫苗，包括在美国使用的辉瑞、Moderna和强生疫苗，以及在海外使用最多的疫苗，如阿斯利康和中国的科兴生物。目前不允许的是俄罗斯的Sputnik V疫苗，该疫苗在70个国家获得授权。世卫组织正在审查人造卫星，但尚未批准。

如果你从墨西哥或加拿大开车来，或者坐渡船来，会怎么样?

陆地边界只对“基本”旅行开放。现在，任何人都可以来，只要他们接种了COVID疫苗。准备向海关和边境保护局出示枪击证据。儿童免于这项要求。

这将如何影响旅行?

尽管美国政府将此描述为重新开放，但一些在大流行早期技术上被允许飞往美国的人现在因其疫苗接种状态而被阻止。恢复正常旅行的其他障碍是美国签证签发的严重延误，大多数国家的人需要签证来美国出差和旅游，以及其他国家的限制，这些限制使旅行变得困难。

例如，尽管来自中国的人现在将被允许进入美国，但由于国内的限制，预计不会有很多人去旅行。在大流行之前，中国游客是美国旅游业的一个利润丰厚的市场。

行业专家确实预计，从欧洲飞来的人将大量涌入，并希望随着全球更多人接种疫苗、美国签证处理速度加快、其他国家取消自己的限制以及人们对因旅行而获得COVID感到不那么害怕，旅行将出现更广泛的复苏。

EXPLAINER: How US rules on international travel are changing

More than a year and a half after COVID-19 concerns prompted the U.S. to close its borders to international travelers from countries including Brazil,China, India, South Africa, theUnited Kingdomand much of Europe, restrictions are shifting to focus on vaccine status.

Beginning Monday, bans on travel from specific countries are over. The U.S. will allow in international travelers, but they must be vaccinated — with a few exceptions.

The U.S. is also reopening the land borders with Canada and Mexico for vaccinated people. Most trips from Canada and Mexico to the U.S. are by land rather than air.

Here are some questions and answers about the changes:

WHY ARE THESE CHANGES HAPPENING?

The goal is to restore more normal travel while limiting the spread of COVID-19, the government says. The travel industry and European allies have pushed for an end to country-specific bans. Americans have been allowed to fly to Europe for months, and Europeans have been pushing the U.S. to change its policies.

In 2019, before the pandemic, about one-fifth of the roughly 79 million visitors to the U.S. came from Europe.

WHAT ARE THE MAIN REQUIREMENTS?

All adult foreign nationals traveling to the U.S. must be fully vaccinated before boarding their flight. Like before, travelers will still have to show proof of a negative COVID-19 test taken within 72 hours of departure to the U.S.

EVERYONE NEEDS TO BE VACCINATED?

Yes, with some exceptions. Children under 18 don't need to be vaccinated but they do need to take a COVID test. Kids 2 and younger are exempt from testing requirements.

WHAT ABOUT ADULTS WHO AREN'T VACCINATED?

Since half the world remains unvaccinated, and vaccine distribution has been so skewed to rich countries, the Biden administration is leaving a loophole for people who live in countries wherevaccinesare scarce. That list includes about 50 countries where fewer than 10% of people have been vaccinated. Travelers from those countries will need permission from the U.S. government to come, and it can't be just for tourism or business travel.

The U.S. government says it will permit unvaccinated international visitors to enter the country if there is a humanitarian or emergency reason, such as an emergency medical evacuation. Those exceptions will be applied “extremely narrowly” and require approval from the Centers for Disease Control and Prevention. There could also be a medical exception, with documentation from a doctor.

WHAT WILL AMERICANS HAVE TO DO?

Americans who are unvaccinated have to show proof of a negative COVID-19 test within one day of international travel. If you're vaccinated, you need to take a test within three days of your departure, for both Americans and citizens of other countries. This does not apply to flights within the U.S.

WHO IS GOING TO ENFORCE THE VACCINE RULES?

That's up to airlines. They will have to verify vaccine records and match them against ID, and if they don't, they could face fines of up to nearly $35,000 per violation. Airlines will also collect information about passengers for contact tracing efforts. There will be CDC workers spot-checking travelers for compliance in the U.S.

WHICH VACCINES WILL LET YOU IN?

Most but not all of them. Any COVID-19 vaccine approved for emergency use by the World Health Organization, which include the Pfizer, Moderna and Johnson & Johnson vaccines used in the U.S. as well as most used overseas, such as AstraZeneca and China's Sinovac. Not currently allowed is Russia’s Sputnik V vaccine, which is authorized in 70 countries. The WHO is reviewing Sputnik but hasn't approved it.

WHAT IF YOU DRIVE IN FROM MEXICO OR CANADA, OR TAKE A FERRY?

The land borders have only been open for “essential” travel. Now, anyone can come, if they're vaccinated against COVID. Be prepared to show proof of the shot to Customs and Border Protection agents. Children are exempt from the requirement.

HOW WILL THIS AFFECT TRAVEL?

While the administration is characterizing this as a reopening, some people who were technically allowed to fly to the U.S. earlier in the pandemic are now blocked because of their vaccination status. Other roadblocks to normal travel resuming are big delays in issuing U.S. visas, which people in most countries need to visit the U.S. for business and tourism, and restrictions in other countries that make travel difficult.

Even though people coming from China will now be allowed into the U.S., for example, not many are expected to travel because of restrictions at home. Before the pandemic, Chinese tourists were a lucrative market for the U.S. travel industry.

Industry experts do expect a big influx in people flying from Europe, and hope that a broader recovery in travel follows as more people globally get vaccinated, U.S. visa processing speeds up, other countries lift their own restrictions and people feel less scared about getting COVID because of travel.