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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.

Consumer watchdog Which? has claimed that more than one billion Android phones and tablets are vulnerable to hackers as they no longer supported by security updates.

According to the research report, the most at-risk phones are any that run Android 4 or older and those smartphones running Android 7.0 which can not be updated are also at risk.

Based on data from Google analysed by Which?, two in five android device users around the world are no longer receiving the important updates. Currently, those devices are unlikely to have issues, but the lack of security leaves them open to attack.

"It is very concerning that expensive Android devices have such a short shelf life before they lose security support, leaving millions of users at risk of serious consequences if they fall victim to hackers," Kate Bevan editor Which? said in a statement.

"Google and phone manufacturers need to be upfront about security updates with clear information about how long they will last and what customers should do when they run out. The government must also push ahead with planned legislation to ensure manufacturers are far more transparent about security updates for smart devices and their impact on consumers," Kate added.

Android phone released around 2012 or earlier, including popular models like the Samsung Galaxy S3 and Sony Xperia S, are particularly at risk to hackers.

Which? has made suggestions to Android users on what to consider if they have an older phone that may be at risk.

Any Android device which is more than two years old, check whether it can be updated to a newer version of the operating system. If it is on an earlier version than Android 7.0 Nougat, try to update via Settings> System>Advanced System update.

In case a user is not able tto update the phone, the device could be at risk of being hacked if it is running a version of Android 4 or lower.

A user also need to be careful about downloading apps outside the Google Play store and should also install a mobile anti-virus via an app.

Amid the rapid spread of the novel coronavirus (COVID-19), which has infected 73 people in India and killed more than 4,500 individuals globally, doctors have advised that in addition to regularly washing hands, one should also disinfect their smartphone every 90 minutes with alcohol-based hand sanitizer.

Ravi Shekhar Jha, Head of Department at Fortis Escorts Hospital in Faridabad said the best method to disinfect your smartphone is to use regular doctor spirit or the alcohol-based hand sanitizer at least every 90 minutes.

"Avoid touching your eyes, mouth, or nose. The best option is to use a phone cover or a Bluetooth device and try to touch your phone as less as possible. We would also recommend cleaning your phone at least twice a day," Jha told IANS.

According to research, published in 2018 by Insurance2Go, a gadget insurance provider, revealed that smartphone screens have three times more germs than a toilet seat.

One in 20 smartphone users was found to clean their phones less than every six months, said the study.

"In the time of fear of coronavirus, smartphones should also be disinfected with alcohol-based sanitizer rub. Pour few drops of sanitizer on a tiny clean cotton pad and rub it safely on your entire phone," said Jyoti Mutta, Senior Consultant, Microbiology, Sri Balaji Action Medical Institute in New Delhi.

"You can repeat this process every evening coming back home after an entire day out at work and once in the morning before going out," Mutta added.

"Maintain basic cleanliness, and try to avoid using other's phones especially if suffering from respiratory illness or flu-like symptoms as there is no other way to disinfect these regular gadgets," she stressed.

Another study from the University of Surrey in the UK, also found that the home button on your smartphone may be harbouring millions of bacteria - some even harmful.

The World Health Organisation (WHO) declared the novel coronavirus as a global pandemic on Wednesday. The death toll of COVID-19 has crossed the 4,500 marks and confirmed cases globally have touched one lakh as per the reports.

According to Suranjeet Chatterjee, Senior Consultant in Internal Medicine Department of Indraprastha Apollo Hospitals in New Delhi, "We should frequently wash our hands, cover our coughs and it is important to adapt to other good hygiene habits that are most important in such a situation."

"Coronavirus and other germs can live on surfaces like glass, metal or plastics and phones are bacteria-ridden. It is necessary that we sanitize our hands frequently and make sure that our hands are clean all the time," Chatterjee told IANS.

"The emphasis should be laid on sanitising our hands rather than sanitizing the phone - once in a while the phone can be sanitized under the guidance of the makers of the phone," Chatterjee stressed.

According to the global health agency, the most effective way to protect yourself against coronavirus is by frequently cleaning of your hands with alcohol-based hand rub or washing them with soap and water.

The WHO's report showed the virus infects people of all ages, among which older people and those with underlying medical conditions are at a higher risk of getting infected.

People should eat only well-cooked food, avoid spitting in public, and avoid close contact, the WHO said, adding that it is important for people to seek medical care at the earliest if they become sick.