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Paris, Apr 17: Even as virologists zero in on the virus that causes COVID-19, a very basic question remains unanswered: do those who recover from the disease have immunity?

There is no clear answer to this question, experts say, even if many have assumed that contracting the potentially deadly disease confers immunity, at least for a while.

"Being immunised means that you have developed an immune response against a virus such that you can repulse it," explained Eric Vivier, a professor of immunology in the public hospital system in Marseilles.

"Our immune systems remember, which normally prevents you from being infected by the same virus later on."

For some viral diseases such a measles, overcoming the sickness confers immunity for life.

But for RNA-based viruses such as Sars-Cov-2 -- the scientific name for the bug that causes the COVID-19 disease -- it takes about three weeks to build up a sufficient quantity of antibodies, and even then they may provide protection for only a few months, Vivier told AFP.

At least that is the theory. In reality, the new coronavirus has thrown up one surprise after another, to the point where virologists and epidemiologists are sure of very little.

"We do not have the answers to that -- it's an unknown," Michael Ryan, executive director of the World Health Organization's Emergencies Programme said in a press conference this week when asked how long a recovered COVID-19 patient would have immunity.

"We would expect that to be a reasonable period of protection, but it is very difficult to say with a new virus -- we can only extrapolate from other coronaviruses, and even that data is quite limited."

For SARS, which killed about 800 people across the world in 2002 and 2003, recovered patients remained protected "for about three years, on average," Francois Balloux director of the Genetics Institute at University College London, said.

"One can certainly get reinfected, but after how much time? We'll only know retroactively."

A recent study from China that has not gone through peer review reported on rhesus monkeys that recovered from Sars-Cov-2 and did not get reinfected when exposed once again to the virus.

"But that doesn't really reveal anything," said Pasteur Institute researcher Frederic Tangy, noting that the experiment unfolded over only a month.

Indeed,several cases from South Korea -- one of the first countries hit by the new coronavirus -- found that patients who recovered from COVID-19 later tested positive for the virus.

But there are several ways to explain that outcome, scientists cautioned.

While it is not impossible that these individuals became infected a second time, there is little evidence this is what happened.

More likely, said Balloux, is that the virus never completely disappeared in the first place and remains -- dormant and asymptomatic -- as a "chronic infection", like herpes.

As tests for live virus and antibodies have not yet been perfected, it is also possible that these patients at some point tested "false negative" when in fact they had not rid themselves of the pathogen.

"That suggests that people remain infected for a long time -- several weeks," Balloux added. "That is not ideal."

Another pre-publication study that looked at 175 recovered patients in Shanghai showed different concentrations of protective antibodies 10 to 15 days after the onset of symptoms.

"But whether that antibody response actually means immunity is a separate question," commented Maria Van Kerhove, Technical Lead of the WHO Emergencies Programme.

"That's something we really need to better understand -- what does that antibody response look like in terms of immunity."

Indeed, a host of questions remain.

"We are at the stage of asking whether someone who has overcome COVID-19 is really that protected," said Jean-Francois Delfraissy, president of France's official science advisory board.

For Tangy, an even grimmer reality cannot be excluded.

"It is possible that the antibodies that someone develops against the virus could actually increase the risk of the disease becoming worse," he said, noting that the most serious symptoms come later, after the patient had formed antibodies.

For the moment, it is also unclear whose antibodies are more potent in beating back the disease: someone who nearly died, or someone with only light symptoms or even no symptoms at all. And does age make a difference?

Faced with all these uncertainties, some experts have doubts about the wisdom of persuing a "herd immunity" strategy such that the virus -- unable to find new victims -- peters out by itself when a majority of the population is immune.

"The only real solution for now is a vaccine," Archie Clements, a professor at Curtin University in Perth Australia, told AFP.

At the same time, laboratories are developing a slew of antibody tests to see what proportion of the population in different countries and regions have been contaminated.

Such an approach has been favoured in Britain and Finland, while in Germany some experts have floated the idea of an "immunity passport" that would allow people to go back to work.

"It's too premature at this point," said Saad Omer, a professor of infectious diseases at the Yale School of Medicine.

"We should be able to get clearer data very quickly -- in a couple of months -- when there will be reliable antibody tests with sensitivity and specificity."

One concern is "false positives" caused by the tests detecting antibodies unrelated to COVID-19.

The idea of immunity passports or certificates also raises ethical questions, researchers say.

"People who absolutely need to work -- to feed their families, for example -- could try to get infected," Balloux.

Google on Monday announced it is gradually winding down its free public Wi-Fi Station programme currently available at over 400 railway stations in India, and will work with the Indian Railways and Railtel Corporation to help them with existing sites so they can remain useful resources for people.

Google launched its Station initiative in India in 2015 to bring fast, free public Wi-Fi to over 400 of the busiest railway stations in the country by mid-2020.

"We crossed that number by June 2018 and implemented Station in thousands of other locations around the country in partnership with telecommunications companies, ISPs and local authorities," Caesar Sengupta, Vice President, Payments and Next Billion Users, Google, said in a statement.

"Over time, partners in other countries asked for Station too and we responded accordingly. We're grateful for these partnerships, especially with the Indian Railways and the Government of India, that helped us serve millions of users over the last few years," he added.

According to Google, the decision to shut Station has been taken keeping the affordable mobile data plans and mobile connectivity in mind that is improving globally including in India.

"India, specifically now has among the cheapest mobile data per GB in the world, with mobile data prices having reduced by 95 per cent in the last 5 years, as per TRAI in 2019," said Sengupta.

The Indian users consume close to 10GB of data, each month, on average, according to reports.

"Our commitment to supporting the next billion users remains stronger than ever, from continuing our efforts to make the internet work for more people and building more relevant and helpful apps and services," Sengupta noted.

Global networking giant Cisco last year teamed up with Google to roll out free, high-speed public Wi-Fi access globally, starting with India.

The first pilot under the partnership was rolled out at 35 locations in Bengaluru.

Sengupta said that in addition to the changed context, the challenge of varying technical requirements and infrastructure among our partners across countries has also made it difficult for Station to scale and be sustainable, especially for our partners.

"And when we evaluate where we can truly make an impact in the future, we see greater need and bigger opportunities in building products and features tailored to work better for the next billion user markets," he said.

While Google is still working on a coronavirus screening and tracking website, Microsoft Bing team has already launched a web portal for tracking COVID-19 infections worldwide.

The website, accessible at bing.com/covid, provides up-to-date infection statistics for each country.

The COVID-19 Tracker currently lists 168,835 as total confirmed cases, 84,558 active cases, 77,761 recovered cases and 6,516 deaths.

There are at least 3,244 confirmed cases of novel coronavirus in the US and at least 61 deaths.

"Lots of Bing folks worked (from home) this past week to create a mapping and authoritative news resource for COVID19 info," Michael Schechter, General Manager for Bing Growth and Distribution at Microsoft, was quoted as saying in a ZDNet report on Sunday.

An interactive map allows site visitors to click on the country to see the specific number of cases and related articles from a variety of publishers.

Data is being aggregated from sources like the World Health Organization (WHO), the US Centers for Disease Control and Prevention (CDC), and the European Centre for Disease Prevention and Control (ECDC).

Microsoft announced the website two days after US President Donald Trump said Google has begun working on COVID-19-related portal for US citizens.

Google's website is being built by Verily, a subsidiary of Alphabet focused on healthcare services.

"More than 1,700 engineers are currently working on the site", Trump said during a press briefing last week.

The tool will triage people who are concerned about their COVID-19 risk into testing sites based on guidance from public health officials and test availability.

Initially, there was some confusion on Google's coronavirus portal but the company later announced that it is "partnering with the US Government in developing a nationwide website that includes information about COVID-19 symptoms, risk, and testing information."