Coronavirus: "a vacherie" that holds surprises - France 24

Paris (AFP)

"This virus is a cowardice", summarizes the French specialist Jean-François Delfraissy: between the concerns on immunity and the symptoms broader than what we thought, the coronavirus reserves many (bad) surprises as and measure research.

- Who is most at risk?

The severity of Covid-19, the disease caused by the new coronavirus, increases with age, as various studies have shown.

Published on March 31 in the British medical journal The Lancet, the latest shows that the disease is on average much more formidable for those over 60 years, with a mortality rate of 6.4% among confirmed cases.

Similarly, this study shows that the proportion of patients requiring hospitalization increases sharply with age: 0.04% for 10/19 year olds, 4.3% for 40/49 year olds, 11.8% for 60 / 69 and 18.4% for those over 80.

The latter figure means that about one in five octogenarians develops a form serious enough to require hospitalization.

Besides age, having a chronic illness is a risk factor.

The most common pathologies in the deceased are hypertension (69.7% of cases), diabetes (32%) and ischemic heart disease (a serious cardiac pathology, 27.7%), according to the last report of the 'Italian Higher Institute of Health (ISS), covering 20,000 dead.

Finally, according to a large analysis published on February 24 by Chinese researchers in the American medical journal Jama, the disease is mild in 80.9% of cases, "serious" in 13.8% of cases and "critical" in 4, 7% of cases.

- How many dead?

If one relates the number of deaths in the world to the total number of officially registered cases, the Covid-19 kills approximately 7% of the diagnosed patients, with disparities according to countries.

But the supposed fatality rate has to be taken with caution as it is unclear how many people have actually been infected. Since many patients seem to develop few or no symptoms, their number is likely to be greater than the cases detected, which would therefore lower this rate.

In addition, countries have very different testing policies and some do not systematically test all suspected cases.

In reality, if we integrate an estimate of undetected cases, "it probably gives a mortality rate around 1%", or "10 times more than the seasonal flu", explained a few weeks ago the American Anthony Fauci, director of the National Institute of Infectious Diseases, before the Congress.

However, the dangerousness of a disease also depends on its ability to spread more or less widely. Even if only 1% of patients die, the number of deaths can be significant if the disease affects a large proportion of the population.

The other factor that aggravates the mortality linked to this new disease is the congestion of hospitals due to a massive influx of cases.

- What symptoms?

"The most common symptoms are fever, fatigue and a dry cough. For some patients, it may also be pain, stuffy nose, runny nose, sore throat or diarrhea," says the organization. world health.

It is often accompanied by respiratory discomfort, which can lead to severe acute respiratory syndrome in the most severe cases.

Symptoms usually last two weeks or more, sometimes less. The aggravation can occur in a second time.

Beyond these types of symptoms, which have been emphasized since the start of the epidemic, it is becoming increasingly clear that the coronavirus also affects the brain and nervous system.

Field observations and several studies have described neurological symptoms: loss of smell and taste, nervous pain, confusion, even seizures and strokes.

Even if there is no certainty, it could be due to the triggering of an overly strong immune response caused by the disease.

Called "cytokine storm", this hyper-inflammatory phenomenon could play a key role in the most severe cases of Covid-19, by attacking the organs.

There is no vaccine or medication, and management involves treating the symptoms. However, some patients are administered antivirals or other experimental treatments, the effectiveness of which is being evaluated.

- What modes of transmission?

The virus is mainly transmitted by respiratory route and physical contact, and it seems that a patient is already contagious even before the first symptoms.

Transmission by respiratory route occurs in the droplets of saliva expelled by the patient, for example when he coughs. Scientists believe that this requires a close contact distance (at least one meter).

In addition, you can become infected by touching an infected object and then putting your hand to your face (eyes, nose, mouth ...).

Two studies published in mid-March and then in mid-April in the American journal NEJM have shown that the new coronavirus is detectable for up to two to three days on plastic or stainless steel surfaces, and up to 24 hours on cardboard.

However, these maximum durations are only theoretical.

"These studies have evaluated the presence of genetic material, and not of live virus", underline the French health authorities on the government.fr official site. However, "it is not because the virus persists that it is enough to infect a person who touches this surface".

"In the opinion of experts, the viral load of the virus (which corresponds to its ability to contaminate) decreases very quickly in the outside environment, and in a few minutes, it is no longer contaminating", continue the French authorities.

Another unknown: the ability of the coronavirus to circulate in suspension in the air and to contaminate in this way (the "aerosols" in scientific jargon).

Object of many conjectures, this mode of transmission is not yet scientifically proven.

To avoid contagion, health authorities emphasize the importance of barrier measures: avoid shaking hands and kissing, washing hands frequently, coughing or sneezing in the crook of one's elbow or in a disposable handkerchief , wear a mask if you are sick ...

- Can we be infected twice?

This crucial question has no firm answer today.

In South Korea, cases of patients tested negative then again positive raise many questions.

The most commonly accepted assumption is that these patients never really healed. Their negative result could be explained either by a very low presence of the virus in the body, or by the fact that the test had been poorly performed.

However, there is still a lack of certainty about the immunity that can be acquired against the coronavirus.

"This virus is a cowardice" and is "devious", according to Jean-François Delfraissy, president of the scientific committee which advises the French authorities.

"We are in the process of asking ourselves the question of whether someone who made a Covid (...) is really so protected as that", he said on April 15 before a parliamentary committee.

He wondered "if we are not completely mistaken" by counting on an immunity comparable to that observed in other diseases. "There are a series of elements that suggest (...) that reactivation phenomena can happen," he concluded.

If this theory were confirmed, it would make it very difficult, if not impossible, to control the epidemic, since the disease could pass several times through the same patient.

© 2020 AFP