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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.

Italian researchers have claimed that they have successfully developed a vaccine to contain coronavirus (COVID-19) which is likely to work on humans, a report said.

Luigi Aurisicchio, CEO of Takis, the firm developing the medication, said that a coronavirus candidate vaccine has neutralised the virus in human cells for the first time, the Arab News reported.

"This is the most advanced stage of testing of a candidate vaccine created in Italy. Human tests are expected after this summer," Aurisicchio was quoted as saying to Italian news agency ANSA.

"According to the Spallanzani Hospital, as far as we know we are the first in the world so far to have demonstrated neutralisation of the coronavirus by a vaccine. We expect this to happen in humans too," he added.

The researchers experimented with the vaccine on mice that had successfully developed antibodies that blocked the virus from infecting the cells. They further observed that the five vaccine candidates generated a large number of antibodies, and selected two with the best results.

All of the vaccine candidates currently being developed are based on the genetic material of DNA protein "spike", the molecular tip used by the coronavirus to enter human cells.

They are injected with the so-called "electroporation" technique, which consists of an intramuscular injection followed by a brief electrical impulse, helping the vaccine break into the cells and activating the immune system, the report said.

Researchers believe that this makes their vaccine particularly effective for generating functional antibodies against the "spike" protein, in particular in the lung cells, which are the most vulnerable to coronavirus.

"We are working hard for a vaccine coming from Italian research, with an all-Italian and innovative technology, tested in Italy and made available to everyone," Aurisicchio was quoted by the Arab News report.

"In order to reach this goal, we need the support of national and international institutions and partners who may help us speed up the process," he noted.

The total number of COVID-19 infections, fatalities and recoveries since the pandemic began has risen to 213,013 in the country.

The coronavirus pandemic has sickened more than 2,425,000 people, according to official counts. So far at least 164,000 people have died, and the virus has been detected in at least 177 countries, as the following table shows.