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Paris, Apr 9: More than 1.5 million cases of the novel coronavirus have been registered worldwide, according to a tally compiled by AFP at 0530 GMT Thursday from official sources.

Of the 1,502,478 infections, 87,320 people have died across 192 countries and territories since the epidemic first emerged in China late last year.

The tallies, using data collected by AFP from national authorities and information from the World Health Organization (WHO), probably reflect only a fraction of the actual number of infections. Many countries are only testing the most serious cases.

May 30: Warning of the tightrope walk ahead as governments battle the coronavirus crisis, Nobel laureate Peter Charles Doherty has expressed concern about densely populated countries such as India relaxing lockdown norms while also describing a complete shutdown as “an economic and social impossibility”.

The Australian immunologist, who cautioned that the number of COVID-19 cases will rise in the coming days, said the earliest time frame for an effective vaccine “going into large numbers of people” is nine to 12 months.

"If all goes well with testing, we could know if some of the candidate vaccines are both safe and effective as early as September/October. Then, rolling a vaccine out will depend on the type of product and how quickly it can be made, put in vials and so forth," Doherty told PTI in an email interview from Melbourne.

The novel coronavirus, he added, does not change fast like influenza and, from what is known so far, “the same vaccine should work everywhere”.

Doherty, who is with the Department of Microbiology and Immunology at the Doherty Institute, University of Melbourne, won the Nobel Prize for Medicine in 1996 for his discovery of how the body’s immune system distinguishes virus-infected cells from normal ones.

Discussing the lockdown, he said, "If it was purely a matter of hard science, everywhere should stay locked down. But that’s pretty much an economic and social impossibility.”

The expectation, he said, is the numbers will rise and limiting spread will depend on people acting responsibly and the capacity for rapid response and extensive contact testing.

“And in a densely populated country like India I think that it will be very difficult," the scientist said.

Several countries, including India, began relaxing lockdown norms in mid-May despite the WHO’s warning about a second wave. India’s lockdown began on March 25 and has since been extended. The fourth phase ends on Sunday.

Asked whether there are any alternatives to a lockdown, the 79-year-old said, "There is no other option other than closing borders. South Korea, for example, conducted massive, intensive testing and contact tracing in a wealthy country with a very disciplined population. Otherwise, not till we have effective vaccines."

He added that he personally doesn’t see the point of closing borders for people coming in if there’s already a high incidence of disease in the community, “unless it’s to avoid the need to care for them and use scarce hospital beds".

According to Doherty, the coronavirus "is a new virus which has come straight out of nature".

“It (the virus) has moved so rapidly across the world because of people travelling on international planes as well as tourist ships," he added.

The immunologist also warned against the use of hydroxychloroquine to treat COVID-19, and said current and planned trials of the anti-malaria drug should be stopped.

“My understanding is that the use of the drug in severe disease is definitely contra-indicated, but it’s not yet clear whether, if taken under medical supervision, it could have some useful effect if taken early on, or as a preventive. Those trials just haven’t been done properly," Doherty noted.

The Indian Council of Medical Research (ICMR) has backed the use of hydroxychloroquine as a preventive against COVID-19 even after the WHO suspended clinical trials of the drug citing safety concerns.

Asked whether plasma therapy can be an effective treatment for COVID-19, Doherty said, "We lack good properly controlled trials but, especially if the plasma has been tested for antibody levels and there’s evidence of good activity, it could be helpful. If I had the disease and was offered plasma therapy I would certainly accept, but I would not take hydroxychloroquine."

Doherty is also very optimistic about herd immunity developing against the SARS-CoV-2 infection.

"We think that (herd immunity) will cut in and have an obvious effect when, say, 60 per cent of people have been infected. Best hope is to boost herd immunity with a vaccine," he stated.

Herd immunity is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through vaccination or previous infections.

The number of COVID-19 cases have crossed 5.9 million and the fatalities 3,65,000, according to the Johns Hopkins University on Saturday. 

In India, the death toll has risen to 4,971 and the number of cases to 1,73,763, according to the Union Health Ministry on Saturday.

Several states, including Bihar, Uttar Pradesh, Madhya Pradesh, Jharkhand and Chhattisgarh, have reported a rise in number since lockdown norms were relaxed in early May and migrant workers reached home.

In Uttar Pradesh, for instance, the number of infections rose from around 3,000 on May 4 to 6,532 on May 26. Similarly, Bihar’s numbers increased from around 500 to over 2,700 in the period.

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.