Coronavirus: the veil is gradually lifting over the disease - France 24

Paris (AFP)

"Coronavirus": unknown to the general public only three months ago, this word is now part of the daily life of billions of humans, who learn every day a little more about this disease fought by doctors around the world.

- 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 people over 60, 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 (respiratory failure, heart disease, history of stroke, cancer ...) is a risk factor.

In a recent report on 10,000 deaths, the Italian Higher Institute of Health (ISS) identified common pathologies in the deceased. The most common are hypertension (73.5% of cases), diabetes (31%) or ischemic heart disease (a serious heart condition, 27%).

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 deaths can we expect?

If one relates the number of deaths in the world to the total number of officially registered cases, Covid-19 kills approximately 5% of the patients diagnosed, 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.

The study published in The Lancet on March 31 estimated the proportion of deaths among the confirmed cases at 1.38%.

However, the danger of a disease does not only depend on the absolute death rate but also on its ability to spread more or less widely.

Even if only 1% of patients die, "it can make significant figures if 30% or 60% of a population is infected," said Dr. Simon Cauchemez, of the Institut Pasteur in Paris.

The other factor that aggravates the mortality linked to this new disease is the congestion of hospitals due to a massive influx of cases. This complicates not only the management of patients with severe forms of Covid-19, but also everyone else.

- What symptoms?

The most common symptoms "include respiratory problems, fever, cough, shortness of breath and difficulty breathing," says WHO. Each of these symptoms may be more or less present depending on the case and the evolution is fluctuating, with ups and downs.

Another common symptom is loss of smell and taste. According to a recent Belgian study carried out on 417 patients who were "non-severely" infected, 86% presented with smell disorders (most of them no longer smelling anything) and 88% with taste disorders.

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

"In the most severe cases, the infection can lead to pneumonia, severe acute respiratory syndrome, kidney failure, and even death," according to the WHO.

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

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 ...

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

A study published in mid-March in the American journal NEJM showed 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, since they are recorded under experimental conditions.

"It is not because a little virus survives that it is enough to infect a person who touches this surface. Indeed, after a few hours, the vast majority of the virus dies and is probably no longer contagious" , underline the French health authorities on the government.fr official site.

Another unknown: the ability of the coronavirus to be transmitted via expired air ("aerosols" in scientific jargon) and not just coughing or sneezing.

The subject of much speculation in recent weeks, this mode of transmission is not yet scientifically proven.

- Can we be infected twice?

Is it possible to be contaminated by the coronavirus, to heal and be tested negative then to be reinfected in stride? A few cases in Asia have raised this question.

To the extent that these cases were isolated, the scientists think that they are undoubtedly explained by the fact that these patients in reality never really cured. The negative test can either come from the fact that it was poorly done, or from a very weak presence of the virus in the body.

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

Based on the example of other viral diseases, specialists believe that once cured, one is temporarily immune, even if this is not yet proven.

However, it is not known how long this supposed immunity lasts. This question is crucial.

"If a person can in theory be immunized for a long period, for example 12 to 24 months, then he can return to public places safely even if the virus is still circulating (...) Conversely, if immunity is very short, a person who has already been infected could be infected again very soon after healing, "says the Center for Strategic and International Studies (CSIS) in Washington.

© 2020 AFP