一个常设大流行专家小组在周四发布的一份报告中预测，新型冠状病毒可能至少要再持续18个月到2年，直到60%到70%的人口被感染。

他们建议美国为最坏的情况做好准备，包括秋季和冬季的第二波冠状病毒感染。他们预测，即使在最好的情况下，也会有人继续死于病毒。

明尼苏达大学传染病研究与政策中心（CIDRAP）主任迈克·奥斯特霍尔姆说，"在60%到70%的人感染之前，病毒不会停止。"

"这一点很快就会得到证实，而如此看待这一问题与微生物学相悖。"

奥斯特霍尔姆撰写关于大流行风险的文章已经20年了，并曾为几位总统提供过建议。这份报告是由其他三位专家共同撰写的，他们是马克·利普西奇，哈佛公共卫生学院流行病学家大流行问题研究顶级专家；克里斯汀·摩尔博士，前疾病控制和预防中心流行病学家，现CIDRAP医学主任；约翰·巴里，历史学家，2004年撰写了关于1918年流感大流行的书《大流感》。

等待群体免疫

他们说，因为Covid-19是新型病毒，没有人有任何免疫力。他们写道："随着群体免疫在人类中逐渐发展，大流行的持续时间可能是18至24个月。"

他们的预测与华盛顿大学卫生计量和评估研究所（IHME）等团体提出的模型或伦敦帝国学院提出的模型不同，后者的报告预测美国和英国将有数百万人死亡，使得两国政府做出强烈的反应。

利普西奇说："我已经说过很久了，当你试图了解传染病将如何发展时，你应该依靠历史和模型。例如，大流行性感染通常不会像季节性流感那样在夏天死亡。"他说。

他们说，只有流感大流行菌株才能与Covid-19相比。

他们在报告中写道："由于潜伏期较长，无症状传播较多，生殖数（R0）较高，COVID-19似乎比流感更容易传播。生殖数（R0）是指每个患者感染其他人员的平均人数。"

"较高的生殖数（R0）意味着，在大流行结束之前需要更多的人感染并免疫。"他们补充道。根据最近的流感大流行，此次疫情可能会持续 18 到 24 个月。

CIDRAP主导的小组为进行综合预测利用这些报告和以往大流行的历史数据发表了有关Covid-19医疗细节的报告。

为最坏的情况做准备

他们说，政府官员应该停止告诉人们大流行可能即将结束，而是为公民做好长期准备。

他们说，有三种情况是可能的：

情景1：2020年春季的第一波Covid-19之后，夏季出现一系列重复的小波，然后持续一至两年，2021年的某个时候逐渐减弱

情景 2：第一波 Covid-19 之后在秋季或冬季出现较大一波，2021 年出现一个或多个小波。他们写道："这种模式要求在秋季恢复缓解措施，以努力减少感染的传播，防止医疗系统不堪重负。"这种模式与1918-19年大流行的情况相似。

方案3：持续传输的"缓慢燃烧"。第三种情况可能不需要恢复缓解措施，尽管病例和死亡将继续发生。

他们建议，各国和地区应规划设想方案2，这是最坏的情况。

他们建议："政府官员应制定具体计划，包括启动缓解措施，以应对疾病高峰时出现疾病高峰。"

利普西奇和奥斯特霍尔姆都表示，他们对许多州决定取消旨在控制病毒传播的限制感到惊讶。

"我认为这是一个实验。这是一个可能夺去生命的实验，特别是在那些不进行仔细控制却试图确定何时再次尝试减缓速度的地方，"利普西奇说。

此外，他说，一些州在决定进行限制的时候感染病例没有那么多，反而在感染病例增加时选择解除限制。

利普西奇说："甚至很难理解这个理由。"

报告说，疫苗可以提供帮助，但速度不会很快。"大流行过程也可能受到疫苗的影响；然而，疫苗可能至少要到2021年的某个时候才能接种，"他们写道。

"我们不知道疫苗开发过程中可能会出现哪些挑战，时间可能会推迟。"

Expert report predicts up to two moreyears of pandemic misery

The new coronavirus is likely to keepspreading for at least another 18 months to two years—until 60% to 70% of thepopulation has been infected, a team of longstanding pandemic experts predictedin a report released Thursday.

They recommended that the US prepare for aworst-case scenario that includes a second big wave of coronavirus infectionsin the fall and winter. Even in a best-case scenario, people will continue todie from the virus, they predicted.

"This thing's not going to stop untilit infects 60 to 70 percent of people," Mike Osterholm, who directs theCenter for Infectious Disease Research and Policy (CIDRAP) at the University ofMinnesota, said.

"The idea that this is going to bedone soon defies microbiology."

Osterholm has been writing about the riskof pandemics for 20 years and has advised several presidents. He wrote thereport along with Harvard School of Public Health epidemiologist Marc Lipsitch,who is also a top expert on pandemics; Dr. Kristine Moore, a former Centers forDisease Control and Prevention epidemiologist who is now medical director forCIDRAP; and historian John Barry, who wrote the 2004 book "The GreatInfluenza" about the 1918 flu pandemic.

Waiting for herd immunity

Because Covid-19 is new, no one has anyimmunity, they said. "The length of the pandemic will likely be 18 to 24months, as herd immunity gradually develops in the human population," theywrote.

Their predictions are different from modelspresented by groups such as the Institute for Health Metrics and Evaluation(IHME) at the University of Washington or the models produced by ImperialCollege London, whose report predicting millions of deaths in the US and UKhelped galvanize responses by both governments.

The CIDRAP-led team used those reports,historical data on past pandemics, and published reports about the medicaldetails of Covid-19 to put together their forecast.

"I have said for a long time that whenyou are trying to understand how infectious disease is going to unfold, youshould rely on history as well as models," Lipsitch said. For instance,pandemic infections don't tend to die down in the summer, like seasonal fludoes., he said.

Covid-19 is most comparable to a pandemicstrain of influenza, they said.

"Because of a longer incubationperiod, more asymptomatic spread, and a higher R0, COVID-19 appears to spreadmore easily than flu," they wrote in the report. R0 is the average numberof other people infected by each patient.

"A higher R0 means more people willneed to get infected and become immune before the pandemic can end," theyadd. "Based on the most recent flu pandemics, this outbreak will likely last18 to 24 months."

Preparing for the worst

They said government officials should stoptelling people the pandemic could be ending and instead prepare citizens for along haul.

Three scenarios are possible, they said:

Scenario 1: The first wave of Covid-19 inspring 2020 is followed by a series of repetitive smaller waves that occurthrough the summer and then consistently over a one- to two-year period,gradually diminishing sometime in 2021

Scenario 2: The first wave of Covid-19 isfollowed by a larger wave in the fall or winter and one or more smaller wavesin 2021. "This pattern will require the reinstitution of mitigationmeasures in the fall in an attempt to drive down spread of infection andprevent healthcare systems from being overwhelmed," they wrote. "Thispattern is similar to what was seen with the 1918-19 pandemic."

Scenario 3: A "slow burn" ofongoing transmission. "This third scenario likely would not require thereinstitution of mitigation measures, although cases and deaths will continueto occur."

States and territories should plan forscenario 2, the worst-case scenario, they recommended.

"Government officials should developconcrete plans, including triggers for reinstituting mitigation measures, fordealing with disease peaks when they occur," they advised.

Lipsitch and Osterholm both said they aresurprised by the decisions many states are making to lift restrictions aimed atcontrolling the spread of the virus.

"I think it's an experiment. It's anexperiment that likely will cost lives, especially in places that do it withoutcareful controls to try to figure out when to try to slow things downagain," Lipsitch said.

Plus, he said, somestates are choosing to lift restrictions when they have more new infectionsthan they had when they decided to impose the restrictions.

"It is hard to even understand therationale," Lipsitch said.

A vaccine could help, the report said, butnot quickly. "The course of the pandemic also could be influenced by avaccine; however, a vaccine will likely not be available until at leastsometime in 2021," they wrote.

"And we don't know what kinds ofchallenges could arise during vaccine development that could delay thetimeline."