Home-made face masks may need at least two layers to stop Covid-19 spread: Study

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.

May 30: Patients undergoing surgery after contracting the novel coronavirus are at an increased risk of postoperative death, according to a new study published in The Lancet journal which may lead to better treatment guidelines for COVID-19.

In the study, the scientists, including those from the University of Birmingham in the UK, examined data from 1,128 patients from 235 hospitals from a total of 24 countries.

Among COVID-19 patients who underwent surgery, they said the death rates approach those of the sickest patients admitted to intensive care after contracting the virus.

The scientists noted that SARS-CoV-2 infected patients who undergo surgery, experience substantially worse postoperative outcomes than would be expected for similar patients who do not have the infection.

According to the study, the 30-day mortality among these patients was nearly 24 per cent.

The researchers noted that mortality was disproportionately high across all subgroups, including those who underwent elective surgery (18.9 per cent), and emergency surgery (25.6 per cent).

Those who underwent minor surgery, such as appendicectomy or hernia repair (16.3 per cent), and major surgery such as hip surgery or for colon cancer also had higher mortality rates (26.9 per cent), the study said.

According to the study, the mortality rates were higher in men versus women, and in patients aged 70 years or over versus those aged under 70 years.

The scientists said in addition to age and sex, risk factors for postoperative death also included having severe pre-existing medical problems, undergoing cancer surgery, undergoing major procedures, and undergoing emergency surgery.

"We would normally expect mortality for patients having minor or elective surgery to be under 1 per cent, but our study suggests that in SARS-CoV-2 patients these mortality rates are much higher in both minor surgery (16.3%) and elective surgery (18.9%)," said study co-author Aneel Bhangu from the University of Birmingham.

Bhangu said these mortality rates are greater than those reported for even the highest-risk patients before the pandemic.

Citing an example from the 2019 UK National Emergency Laparotomy Audit report, he said the 30-day mortality was 16.9 per cent in the highest-risk patients.

Based on an earlier study across 58 countries, Bhangu said the 30-day mortality was 14.9 per cent in patients undergoing high-risk emergency surgery.

"We recommend that thresholds for surgery during the SARS-CoV-2 pandemic should be raised compared to normal practice," he said.

"For example, men aged 70 years and over undergoing emergency surgery are at particularly high risk of mortality, so these patients may benefit from their procedures being postponed," Bhangu added.

The study also noted that patients undergoing surgery are a vulnerable group at risk of SARS-CoV-2 exposure in hospital.

It noted that the patients may also be particularly susceptible to subsequent pulmonary complications, due to inflammatory and immunosuppressive responses to surgery and mechanical ventilation.

The scientists found that overall in the 30 days following surgery 51 per cent of patients developed a pneumonia, acute respiratory distress syndrome, or required unexpected ventilation.

Nearly 82 per cent of the patients who died had experienced pulmonary complications, the researchers said.

"Worldwide an estimated 28.4 million elective operations were cancelled due to disruption caused by COVID-19," said co-author Dmitri Nepogodiev from the University of Birmingham.

"Our data suggests that it was the right decision to postpone operations at a time when patients were at risk of being infected with SARS-CoV-2 in hospital," Nepogodiev said.

According to the researchers, there's now an urgent need for investment by governments and health providers in to measures which ensure that as surgery restarts patient safety is prioritised.

They said this includes the provision of adequate personal protective equipment (PPE), establishment of pathways for rapid preoperative SARS-CoV-2 testing, and consideration of the role of dedicated 'cold' surgical centres.

In a study conducted in 117 countries, researchers have found that the world is experiencing the most dramatic reduction in the seismic noise (the hum of vibrations in the planet's crust) in recorded history due to global COVID-19 lockdowns.

Measured by instruments called seismometers, seismic noise is caused by vibrations within the Earth, which travel like waves and the waves can be triggered by earthquakes, volcanoes, and bombs - but also by daily human activity like travel and industry.

This quiet period was likely caused by the total global effect of social distancing measures, closure of services and industry, and drops in tourism and travel, the study published in the journal Science, reported.

The new research, led by the Royal Observatory of Belgium and five other institutions around the world including Imperial College London (ICL), showed that the dampening of 'seismic noise' caused by humans was more pronounced in more densely populated areas.

"Our study uniquely highlights just how much human activities impact the solid Earth, and could let us see more clearly than ever what differentiates human and natural noise," said study co-author Stephen Hicks from ICL in the UK.

For the findings, the research team looked at seismic data from a global network of 268 seismic stations in 117 countries and found significant noise reductions compared to before any lockdown at 185 of those stations.

Researchers tracked the 'wave' of quietening between March and May as worldwide lockdown measures took hold.

The largest drops in vibrations were seen in the most densely populated areas, like Singapore and New York City, but drops were also seen in remote areas like Germany's the Black Forest and Rundu in Namibia.

Citizen-owned seismometers, which tend to measure more localised noise, noted large drops around universities and schools around Cornwall, UK and Boston, US - a drop in noise 20 per cent larger than seen during school holidays.

The findings showed that countries like Barbados, where lockdown coincided with the tourist season, saw a 50 per cent decrease in noise.

"The changes have also given us the opportunity to listen in to the Earth's natural vibrations without the distortions of human input," the study authors wrote.

Earlier in April, a study published in the journal Nature, reported at least a 30 per cent reduction in that amount of ambient human noise since lockdown began in Belgium.