Karl Manke, 77, left, wears a mask while cutting hair, Tuesday, May 5, 2020 at Karl Manke's Barber and Beauty Shop in Owosso, Mich. Manke re-opened his doors on Monday in defiance of Gov. Gretchen Whitmer's executive order mandating salons, barbershops and other businesses to stay closed. He has already given nearly 100 haircuts, and fields more calls than that daily, all while continuing to cut hair. (Jake May/The Flint Journal via AP)

As Europe and the U.S. loosen their lockdowns against the coronavirus, health experts are expressing growing dread over what they say is an all-but-certain second wave of deaths and infections that could force governments to clamp back down.

"We're risking a backslide that will be intolerable," said Dr. Ian Lipkin of Columbia University's Center for Infection and Immunity.

Elsewhere around the world, German authorities began drawing up plans in case of a resurgence of the virus. Experts in Italy urged intensified efforts to identify new victims and trace their contacts. And France, which hasn't yet eased its lockdown, has already worked up a "reconfinement plan" in the event of a new wave.

"There will be a second wave, but the problem is to which extent. Is it a small wave or a big wave? It's too early to say," said Olivier Schwartz, head of the virus unit at France's Pasteur Institute.

In the U.S., with about half of the states easing their shutdowns to get their economies restarted and cellphone data showing that people are becoming restless and increasingly leaving home, public health authorities are worried.

Many states have not put in place the robust testing that experts believe is necessary to detect and contain new outbreaks. And many governors have pressed ahead before their states met one of the key benchmarks in the Trump administration's guidelines for reopening—a 14-day downward trajectory in new illnesses and infections.

A worker is seen through a steel tube at MAP, a factory operating in design, manufacture and installation of steel structures for civil and industrial use, in Corsico, near Milan, Italy, Wednesday, May 6, 2020. Italy began stirring again after the coronavirus shutdown, with 4.4 million Italians able to return to work and restrictions on movement eased in the first European country to lock down in a bid to stem COVID-19 infections. (AP Photo/Antonio Calanni)

"If we relax these measures without having the proper public health safeguards in place, we can expect many more cases and, unfortunately, more deaths," said Josh Michaud, associate director of global health policy with the Kaiser Family Foundation in Washington.

Cases have continued to rise steadily in places such as Iowa and Missouri since the governors began reopening, while new infections have yo-yoed in Georgia, Tennessee and Texas.

Lipkin said he is most worried about two things: the reopening of bars, where people crowd together and lose their inhibitions, and large gatherings such as sporting events, concerts and plays. Preventing outbreaks will require aggressive contact tracing powered by armies of public health workers hundreds of thousands of people strong, which the U.S. doesn't yet have, Lipkin said.

Customers Randy and Nancy Cree eat dinner in the dining room of the Chic-A-Dee Cafe In Topeka, Kan., Tuesday, May 5, 2020. Some booths are closed in order to maintain distance. Restaurant dining rooms, retail stores and some offices began reopening Monday after Kansas lifted a statewide stay-at-home order. (AP Photo/Orlin Wagner)

Worldwide the virus has infected more than 3.6 million people and killed over a quarter-million, according to a tally by Johns Hopkins University that experts agree understates the dimensions of the disaster because of limited testing, differences in counting the dead and concealment by some governments.

The U.S. has recorded over 70,000 deaths and 1.2 million confirmed infections, while Europe has reported over 140,000 dead.

This week, the researchers behind a widely cited model from the University of Washington nearly doubled their projection of deaths in the U.S. to about 134,000 through early August, in large part because of the easing of state stay-at-home restrictions. Newly confirmed infections per day in the U.S. exceed 20,000, and deaths per day are running well over 1,000.

In hard-hit New York City, which has managed to bring down deaths dramatically even as confirmed infections continue to rise around the rest of the country, Mayor Bill de Blasio warned that some states may be reopening too quickly.

A female student wearing a protective face mask to help curb the spread of the new coronavirus checks temperature of her classmates at a high school in Wuhan in central China's Hubei province, Wednesday, May 6, 2020. Senior students returned to classes on Wednesday in the central Chinese city of Wuhan, the epicenter of the coronavirus pandemic, after no new cases or deaths were reported from the outbreak that had prompted a 76-day quarantine in the city of 11 million. (Chinatopix via AP)

"My message to the rest of the country is learn from how much effort, how much discipline it took to finally bring these numbers down and follow the same path until you're sure that it's being beaten back," he said on CNN, "or else if this thing boomerangs, you're putting off any kind of restart or recovery a hell of a lot longer."

A century ago, the Spanish flu epidemic's second wave was far deadlier than its first, in part because authorities allowed mass gatherings from Philadelphia to San Francisco.

"It's clear to me that we are in a critical moment of this fight. We risk complacency and accepting the preventable deaths of 2,000 Americans each day," epidemiologist Caitlin Rivers, a professor at Johns Hopkins, told a House subcommittee in Washington.

President Donald Trump, who has pressed hard to ease the restrictions that have throttled the economy and thrown more than 30 million Americans out of work, pulled back Wednesday on White House plans revealed a day earlier to wind down the coronavirus task force.

Valentina Bacchin, wearing a sanitary mask to protect against COVID-19 looks at Wilfy, a young westie dog needing a haircut, in the Bottega di Zula pet grooming shop in Rome, Wednesday, May 6, 2020. Bacchin reopened her shop on Monday when Italy began stirring again after a two-month coronavirus shutdown, with 4.4 million Italians able to return to work and restrictions on movement eased in the first European country to lock down in a bid to stem COVID-19 infections. (AP Photo/Alessandra Tarantino)

He tweeted that the task force will continue meeting indefinitely with a "focus on SAFETY & OPENING UP OUR COUNTRY AGAIN."

Underscoring those economic concerns, the European Union predicted the worst recession in its quarter-century history. And the U.S. unemployment rate for April, which comes out Friday, is expected to hit a staggering 16 percent, a level last seen during the Great Depression of the 1930s.

Governors continue to face demands, even lawsuits, to reopen. In Michigan, where armed demonstrators entered the Capitol last week, the Republican-led Legislature sued Democratic Gov. Gretchen Whitmer, asking a judge to declare invalid her stay-at-home order, which runs at least through May 15.

In hard-hit Italy, which has begun easing restrictions, Dr. Silvio Brusaferro, president of the Superior Institute of Health, urged "a huge investment" of resources to train medical personnel to monitor possible new cases of the virus, which has killed about 30,000 people nationwide.

Residents of the Paraisopolis slum attend a ceremony on a soccer field after getting basic training from health workers on how to stay safe during the COVID-19 pandemic in their community in Sao Paulo, Brazil, Wednesday, May 6, 2020. With over 100,000 residents, Paraisopolis is one of the areas of Sao Paulo most affected by the new coronavirus. (AP Photo/Andre Penner)

He said that contact-tracing apps—which are being built by dozens of countries and companies—aren't enough to manage future waves of infection.

German Chancellor Angela Merkel said after meeting with the country's 16 governors that restaurants and other businesses will be allowed to reopen in coming weeks but that regional authorities will have to draw up a "restriction concept" for any county that reports 50 new cases for every 100,000 inhabitants within a week.

Britain, with over 30,000 dead, the second-highest death toll in the world behind the U.S., plans to extend its lockdown but has begun recruiting 18,000 people to trace contacts of those infected.

On Thursday, New Zealand Prime Minister Jacinda Ardern outlined a plan for a further relaxation of its lockdown rules, under which the country would reopen bars, retail stores and hair salons beginning next week and once again allow domestic travel.

  • Nathan Golub, left, Operations Manager of Surgical Services and Angela Wilson, Coordinator of Transplant Programs at Baylor Scott & White Hospital watch as the U.S. Navy Blue Angels fly over their hospital in Dallas, Wednesday, May 6, 2020. (AP Photo/Tony Gutierrez)

  • People from the low-income neighborhood of Klong Toey wait to get tested for the coronavirus in Bangkok, Thailand, Wednesday, May 6, 2020. Thai health workers started testing community of about 1600 people of the Klong Toey area at a nearby Buddhist temple. (AP Photo/Gemunu Amarasinghe)

  • Medical workers take a break at a coronavirus mobile test site in Jakarta, Indonesia, Wednesday, May 6, 2020. The Indonesian Election Commission has decided to postpone preparations for Sept. 23, 2020, regional elections until at least December later this year after a number of organizers got sick with virus. (AP Photo/Dita Alangkara)

  • People rest and exercising on park in Barcelona, Spain, Wednesday, May 6, 2020. Spain has implemented time slots for different groups like sport and exercise, for elders and for children, to control release of the population from lockdown while controlling the spread of coronavirus. Spain's government has extended the country's current state of emergency for another 15 days. Spain has recorded over 25,600 deaths from the new coronavirus. (AP Photo/Emilio Morenatti)

  • Migrant laborers and their family members, who arrived from Gujarat state on a train, wave from inside a bus as they prepare to leave for their native villages in their home state of Uttar Pradesh in Prayagraj, India, Wednesday, May 6, 2020. India is running train service for thousands of migrant workers desperate to return home since it imposed a nationwide lockdown to control the spread of the coronavirus. (AP Photo/Rajesh Kumar Singh)

  • Familihulp home healthcare worker Nathalie Deroost, wears a face mask to protect against the spread of coronavirus, as she speaks with her client, former truck driver Jerome Demeyer, 86, at his house in Bierbeek, Belgium, Wednesday, May 6, 2020. Belgium is relaxing some of its lockdown measures Monday. Business-to-business companies can open their offices to employees again and those taking public transport must wear a mask. (AP Photo/Francisco Seco)

  • Homeless people sleep on a train at the Coney Island Stillwell Avenue Terminal Wednesday, May 6, 2020, in the Brooklyn borough of New York. (AP Photo/Frank Franklin II)

  • People pass by wearing face masks to protect against the spread of the new coronavirus as ride along a street in Beijing, Wednesday, May 6, 2020. China on Wednesday reported just two new cases of the coronavirus and no deaths. (AP Photo/Mark Schiefelbein)

  • A banner in Italian reads: "If we open we go bankrupt!" as restaurant and bar owners protest against limited reopening in Milan, Italy, Wednesday, May 6, 2020. Hundreds of Milan bar and restaurant owners each placed an empty chair from their establishments in front of the Arco della Pace triumphal arc Wednesday in a protest demanding fiscal and other measures to help them survive the lockdown. Restaurants and bars can presently prepare take-away food and drinks for customers and will only open for sit-down clients from June 1. (Claudio Furlan/LaPresse via AP)

  • Cars and trucks are driven on a relatively empty highway in Frankfurt, Germany, Wednesday, May 6, 2020. Due to the coronavirus a lot less traffic is seen during the day. (AP Photo/Michael Probst)

In other developments, the U.S. Centers for Disease Control and Prevention said nearly 5,000 coronavirus illnesses and at least 88 deaths have been reported among inmates in American jails and prisons. An additional 2,800 cases and 15 deaths were reported among guards and other staffer members.

A 57-year-old immigration detainee at Otay Mesa Detention Center in San Diego died Wednesday from complications related to the coronavirus, authorities said, marking the first reported death from the virus among about 30,000 people in U.S. immigration custody. Otay Mesa has been a hotbed for the spread of the coronavirus.