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Washington, Jul 1: The United States has approved four coronavirus vaccine candidates for clinical trials, Food and Drug Administration (FDA) head Stephen Hahn told reporters.

"Four vaccines have been approved for moving into clinical trials... and another six are in the pipeline for us to review," Hahn said during a press briefing on Tuesday.

The US Administration launched in May Operation Warp Speed, a joint project of Health and Defense Departments, which aims to deliver 300 million doses of a vaccine for COVID-19 by January 2021.

The country's top pandemics expert Anthony Fauci warned on Tuesday, however, that there is no certainty the United States will be able to develop a vaccine against COVID-19 that works and will be safe.

Data on vaccine effectiveness, he added, may be available in the winter or early next year.

Houston, Mar 15: Researchers, studying the novel coronavirus, have found that the time between cases in a chain of transmission is less than a week, and over 10 per cent of patients are infected by someone who has the virus, but does not show symptoms yet, a finding that may help public health officials contain the pandemic.

The study, published in the journal Emerging Infectious Diseases, estimated what's called the serial interval of the coronavirus by measuring the time it takes for symptoms to appear in two people with the virus -- the person who infects another, and the infected second person.

According to the researchers, including those from the University of Texas at Austin, the average serial interval for the novel coronavirus in China was approximately four days.

They said the speed of an epidemic depends on two things -- how many people each case infects, and how long it takes cases to spread.

The first quantity, the scientists said, is called the reproduction number, and the second is the serial interval.

Due to the short serial interval of the disease caused by the coronavirus -- COVID-19 -- they said, emerging outbreaks will grow quickly, and could be difficult to stop.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days,” said Lauren Ancel Meyers, study co-author from UT Austin.

Meyers explained that public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others.

“The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat,” Meyers added.

In the study, the scientists examined more than 450 infection case reports from 93 cities in China, and found the strongest evidence yet that people without symptoms must be transmitting the virus -- known as pre-symptomatic transmission.

More than one in ten infections were from people who had the virus but did not yet feel sick, the scientists said.

While researchers across the globe had some uncertainty until now about asymptomatic transmission with the coronavirus, the new evidence could provide guidance to public health officials on how to contain the spread of the disease.

“This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Meyers said.

The researchers cautioned that asymptomatic transmission makes containment more difficult.

With hundreds of new cases emerging around the world every day, the scientists said, the data may offer a different picture over time.

They said infection case reports are based on people's memories of where they went and whom they had contact with, and if health officials move quickly to isolate patients, that may also skew the data.

“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide. This tells us that COVID-19 outbreaks can be elusive and require extreme measures,” Meyers said.

Washington, Mar 29: The number of known coronavirus US cases soared well past 115,000, with more than 1,900 dead, as President Donald Trump said on Saturday he was considering imposing a quarantine on the hard hit New York region.

American healthcare workers in the trenches of the pandemic are appealing for more protective gear and equipment to treat a surge in patients that is already pushing hospitals to their limits in virus hot spots such as New York City, New Orleans and Detroit.

Trump told reporters he could order a quarantine on three states, New York, New Jersey and Connecticut, which between them have recorded at least 64,000 infections and 895 deaths.

He also appeared to soften his previous comments calling for the US economy to be swiftly reopened. Asked whether he thought the United States would restart by Easter Sunday, April 12, Trump replied, "We'll see, what happens."

New York Governor Andrew Cuomo said he had no details on any possible quarantine order for his state, telling a briefing: "I don't even know what that means. I don't know how that would be legally enforceable, and from a medical point of view I don't know what you would be accomplishing."

He said New York was postponing its presidential primary election to June 23, from April 28.

As the crisis deepened, nurses at Jacobi Medical Center in New York's borough of the Bronx protested outside the hospital on Saturday, saying supervisors asked them to reuse personal protective equipment, including masks. Some held signs with slogans including "Protect our lives so we can save yours."

"The masks are supposed to be one-time use," one nurse said, according to videos posted online. "Now, all of a sudden the CDC (Centers for Disease Control and Prevention) is saying that it's fine for us to reuse them. These choices are being made not based on science. They're being made based on need."

One resident at New York Presbyterian Hospital said they were issued with just one mask.

"This is your mask forever. You can bring it home with you. Here's how you can clean your mask," said the resident, who asked not to be named because he was not authorized to speak to the media. "It's not the people who are making these decisions that go into the patients' rooms."

Doctors are also especially concerned about a shortage of ventilators, machines that help patients breathe and are widely needed for those suffering from COVID-19, the pneumonia-like respiratory ailment caused by the highly contagious novel coronavirus.

Hospitals have also sounded the alarm about scarcities of drugs, oxygen tanks and trained staff.

By Saturday afternoon, the US number of cases stood at 115,842 with at least 1,929 deaths, according to a Reuters tally. The United States has had the most recorded cases of any country since its count of infections eclipsed those of China and Italy on Thursday.

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As shortages of key medical supplies abounded, desperate physicians and nurses were forced to take matters into their own hands.

New York-area doctors say they have had to recycle some protective gear, or even resort to bootleg suppliers.

Dr. Alexander Salerno of Salerno Medical Associates in northern New Jersey described going through a "broker" to pay $17,000 for masks and other protective equipment that should have cost about $2,500, and picking them up at an abandoned warehouse.

"You don't get any names. You get just phone numbers to text," Salerno said. "And so you agree to a term. You wire the money to a bank account. They give you a time and an address to come to."

Nurses at Mount Sinai Hospital in New York said they were locking away or hiding N95 respirator masks, surgical masks and other supplies that are prone to pilfering if left unattended.

"Masks disappear," nurse Diana Torres said. "We hide it all in drawers in front of the nurses' station."

One nurse at Westchester Medical Center, in the suburbs of the city, said colleagues have begun absconding with scarce supplies without asking, prompting better-stocked teams to lock masks, gloves and gowns in drawers and closets.

An emergency room doctor in Michigan, an emerging epicenter of the pandemic, said he was wearing one paper face mask for an entire shift due to a shortage and that hospitals in the Detroit area would soon run out of ventilators.

"We have hospital systems here in the Detroit area in Michigan who are getting to the end of their supply of ventilators and have to start telling families that they can't save their loved ones because they don't have enough equipment," the physician, Dr. Rob Davidson, said in a video posted on Twitter.

Sophia Thomas, a nurse practitioner at DePaul Community Health Center in New Orleans, where Mardi Gras celebrations late last month fueled an outbreak in Louisiana's largest city, said the numbers of coronavirus patients "have been staggering."

In the nation's second-largest city, Los Angeles Mayor Eric Garcetti said spiking cases were putting Southern California on track to match New York City's infection figures in the next week.