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COVID-19 mostly kills through an overreaction of the immune system, whose function is precisely to fight infections, say scientists who have decoded the mechanisms, symptoms, and diagnosis of the disease caused by the SARS-Cov-2 coronavirus.

In a study published in the journal Frontiers in Public Health, the researchers explained step-by-step how the virus infects the airways, multiplies inside cells, and in severe cases causes the immune defences to overshoot with a "cytokine storm".

This storm is an over-activation of white blood cells, which release too-great amounts of cytokines -- inflammation-stimulating molecules --into the blood, they said.

"Similar to what happens after infection with SARS and MERS, data show that patients with severe COVID-19 may have a cytokine storm syndrome," said study author Daishun Liu, Professor at Zunyi Medical University in China.

"The rapidly increased cytokines attract an excess of immune cells such as lymphocytes and neutrophils, resulting in an infiltration of these cells into lung tissue and thus cause lung injury," Liu said.

The researchers explained that the cytokine storm ultimately causes high fever, excessive leakiness of blood vessels, and blood clotting inside the body.

It also causes extremely low blood pressure, lack of oxygen and excess acidity of the blood, and build-up of fluids in the lungs, they said.

The researchers noted that white blood cells are misdirected to attack and inflame even healthy tissue, leading to failure of the lungs, heart, liver, intestines, kidneys, and genitals.

This multiple organ dysfunction syndrome (MODS) may worsen and shutdown the lungs, a condition called acute respiratory distress syndrome, (ARDS), they said.

This, the researchers explained, happens due to the formation of a so-called hyaline membrane -- composed of debris of proteins and dead cells -- lining the lungs, which makes absorption of oxygen difficult.

Most deaths due to COVID-19 are therefore due to respiratory failure, they said.

The researchers explained that in the absence of a specific antiviral cure for COVID-19, the goal of treatment must be to the fight the symptoms, and lowering the mortality rate through intensive maintenance of organ function.

For example, an artificial liver blood purification system or renal replacement therapy can be used to filter the blood through mechanical means, they said.

The team noted that especially important are methods to supplement or replace lung function, for example with non-invasive mechanical ventilation through a mask, ventilation through a tube into the windpipe, the administration of heated and humidified oxygen via a tube in the nose, or a heart-lung bypass.

The researchers stressed the importance of preventing secondary infections.

They noted that SARS-Cov-2 also invades the intestines, where it causes inflammation and leakiness of the gut lining, allowing the opportunistic entry of other disease-causing microorganisms.

The researchers advocate that this should be prevented with nutritional support, for example with probiotics -- beneficial bacteria that protect against the establishment of harmful ones -- and nutrients and amino acids to improve the immune defences and function of the intestine.

"Because treatment for now relies on aggressive treatment of symptoms, preventative protection against secondary infections, such as bacteria and fungi, is particularly important to support organ function, especially in the heart, kidneys, and liver, to try and avoid further deterioration of their condition," Liu added.

The World Health Organisation on Wednesday said that anti-malarial drug hydroxychloroquine (HCQ) will return to the solidarity trial for the potential treatment of coronavirus disease.

At a press conference in the WHO headquarters in Geneva, Director General Tedros Adhanom Ghebreyesus said: "On the basis of the available mortality data, the members of the committee recommended that there are no reasons to modify the trial protocol. The Executive Group received this recommendation and endorsed continuation of all arms of the solidarity trial, including hydroxychloroquine."

The world health body had temporarily suspended the usage of HCQ from the solidarity trial for coronavirus treatment on May 25 soon after a study published in one of the most reliable medical journals, which had suggested that the drug could cause more fatalities among COVID-19 patients.

However, the WHO chief said that the decision was taken as a precaution while the safety data was reviewed.

Ghebreyesus also said that the Data Safety and Monitoring Committee will continue to closely monitor the safety of all therapeutics being tested in the solidarity trial.

"So far, more than 3,500 patients have been recruited in 35 countries. WHO is committed to accelerating the development of effective therapeutics, vaccines and diagnostics as part of our commitment to serving the world with science, solutions and solidarity," he said.

Soon after HCQ was suspended from the trial, the Indian government had said that the antimalarial drug has been known for its benefits for a long time and its usage will be continued on the frontline workers, including police and healthcare professionals, as prophylaxis. The government had also said that studies were being conducted and the drug would be included in the clinical trial also for the treatment of coronavirus disease.

US President Donald Trump also had strongly advocated the use of HCQ and called it a "game-changer". He went to the extent of saying that he had taken the medicine.

Launched by WHO and partners, solidarity trial is an international clinical trial to find an effective treatment for COVID-19, including drugs to slow the progression of the disease or improve survival. The trial, which enrols patients from different countries, "will compare four treatment options against standard of care to assess their relative effectiveness against COVID-19", said WHO. 

The health and future of every child and adolescent worldwide is under immediate threat from ecological degradation, climate change and exploitative marketing practices that push fast food, sugary drinks, alcohol and tobacco at children, said a new report on Wednesday.

No single country is adequately protecting children's health, their environment and their futures, according to the report by a commission of over 40 child and adolescent health experts from around the world.

The commission, convened by the World Health Organization (WHO), the United Nations children's agency, Unicef, and medical journal the Lancet, found that while the poorest countries need to do more to support their children's ability to live healthy lives, excessive carbon emissions --disproportionately from wealthier countries -- threaten the future of all children.

"Despite improvements in child and adolescent health over the past 20 years, progress has stalled, and is set to reverse," said former Prime Minister of New Zealand and Co-Chair of the Commission, Helen Clark.

"It has been estimated that around 250 million children under five years old in low- and middle-income countries are at risk of not reaching their developmental potential, based on proxy measures of stunting and poverty. But of even greater concern, every child worldwide now faces existential threats from climate change and commercial pressures," Clark said.

The report, titled "A Future for the World's Children?", includes a new global index of 180 countries, comparing performance on child flourishing and sustainability, with a proxy for greenhouse gas emissions, and equity, or income gaps.

India ranked 131 among the 180 countries in the index.

The index shows that children in Norway, the Republic of Korea, and the Netherlands have the best chance at survival and well-being, while children in the Central African Republic, Chad, Somalia, Niger and Mali face the worst odds.

However, when the authors took per capita CO2 emissions into account, the top countries trail behind: Norway ranked 156, the Republic of Korea 166, and the Netherlands 160.

Each of the three emits 210 per cent more CO2 per capita than their 2030 target.

The US, Australia, and Saudi Arabia are among the ten worst emitters.

If global warming exceeds 4 degree Celsius by the year 2100 in line with current projections, this would lead to devastating health consequences for children, due to rising ocean levels, heatwaves, proliferation of diseases like malaria and dengue, and malnutrition, said the report.

The only countries on track to beat CO2 emission per capita targets by 2030, while also performing fairly (within the top 70) on child flourishing measures are: Albania, Armenia, Grenada, Jordan, Moldova, Sri Lanka, Tunisia, Uruguay and Vietnam.

The report also revealed the distinct threat posed to children from harmful marketing. Evidence suggests that children in some countries see as many as 30,000 advertisements on television alone in a single year, while youth exposure to vaping (e-cigarettes) advertisements increased by more than 250 per cent in the US over two years, reaching more than 24 million young people.

Children's exposure to commercial marketing of junk food and sugary beverages is associated with purchase of unhealthy foods and overweight and obesity, linking predatory marketing to the alarming rise in childhood obesity, said the report.

The number of obese children and adolescents increased from 11 million in 1975 to 124 million in 2016 - an 11-fold increase, with dire individual and societal costs.