Mortality rate? Risk of infection? Transmission? What Scientists Learned – Knowledge

Status as of March 7, 2020

We are still at the start of the Sars-CoV-2 epidemic. Researchers adapt their knowledge and conclusions as new data becomes available. Here’s what scientists know:

According to the latest calculations, the mortality rate from Covid-19 disease in all age groups is 1.1% for cases with symptoms (case fatality rate). If cases without symptoms are also included, this rate is 0.5% (mortality rate from infection). Adam Kucharski, mathematician and epidemiologist at the London School of Hygiene & Tropical Medicine, recently calculated these values. Among young people, the value decreases (0.1%), among the elderly, it increases (5 to 10%), as he explains in the “New York Times”. These values ​​are also confirmed by the Swiss epidemiologist Christian Althaus on Twittereven if its calculated mortality rate of 1.6% for all age groups is slightly higher. These figures clearly show what a large part of scientists have been saying for some time now: Covid-19 is five to fifteen times more dangerous in terms of mortality than seasonal flu. For influenza, the mortality rate is 0.02 to 0.1%. There are up to 90 million cases of influenza each year worldwide, with 200,000 to 650,000 deaths, and between 300 and 2,500 deaths per year in Switzerland.

The elderly are particularly at risk. The risk of complications increases considerably after the age of 65. People with pre-existing conditions should also be protected. In Italy, according to health authorities, the average age of the first 105 deaths was 81, most of them suffering from chronic diseases and were men. The average age of those who died from Covid-19 in China was 70, according to a study published in “The Lancet”. “The data shows that about half of those who died suffered from other illnesses such as diabetes or high blood pressure. But conversely, 30 to 50% of those who died were also in good health, “says Manuel Battegay, professor of infectious diseases at the University of Basel. A team of scientists led by Christian Althaus recently conducted a study to calculate the mortality rate according to age groups. This is case data from the Chinese province in Hubei crisis.

The calculations of Althaus and colleagues are consistent with the largest study to date on the aspect of age and mortality rates: A study “> We presented in detail the study of 44,672 confirmed cases of Covid 19 in mainland China until February 11, 2020, published in the “Chinese Journal of Epidemiology”.

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Evolution of the disease
80% of people infected with Covid-19 have mild conditions. The vast majority of the population will tolerate the infection very well, some will not notice anything. But what exactly does “light” mean? According to, epidemic expert at the WHO, these are not always simple cold symptoms. “Mild” can also mean fever, cough – maybe even pneumonia, but without the need for artificial oxygenation. In 20% of severe cases, the respiratory rate is increased and the oxygen saturation decreases, so it is necessary to use an additional oxygen supply or a respirator. Critical (5%) means respiratory failure or failure of several organs. ” Doctors in northern Italy state in that 10% of cases require intensive medical care.

Children and pregnant women
Children can also be infected, but in most cases they develop no symptoms or only very mild symptoms. We still don’t know if they can spread the virus. Bruce Aylward, an epidemic expert at WHO, said after a study visit to China: “I asked dozens of doctors: did you see a chain of transmission from a child? The answer was no. ” Preliminary data suggests that children are more likely to be infected by adults, but that adults are less likely to be infected by children. Children were also less likely to be affected by the Sras and the Seas. “One theory is that the landing sites in the lungs are even less pronounced for Sars-CoV-2. We still still do not understand in whom 2019-nCoV will lead to a serious illness with pneumonia or to a mild course, “says Manuel Battegay, professor of infectious diseases at the University of Basel. The situation is different with influenza: children are also considered to be at risk groups particularly affected by severe forms of the flu. And they are important drivers of the transmission of influenza viruses in the community. The New York Times has explored in more detail the reasons why children get Covid-19 so rarely and why it is almost always minor. There are no clear answers yet. According to the WHO, pregnant women do NOT belong to groups at risk for Covid-19 according to current knowledge.

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The Covid-19 is relatively easy to transfer. Jeremy Farrar, medical specialist in infections, says: “What we are seeing now is unprecedented. I have never seen an epidemic that has spread so quickly in the past 100 years. ” The level of contagion of a virus is determined by the so-called R0 value, which indicates how many more people a single infected person will infect. Using a computer model, the EPFZ has calculated that an average person infected with coronavirus infects between 2 and 3.5 other people. The coronavirus is therefore more contagious than the seasonal flu, which has an R0 value of 1.3 to 3. As long as the R0 value of a virus is greater than 1, it can continue to spread in the population. Below 1, it gradually disappears. In the hardest-hit Chinese city of Wuhan, the average of 2.35 was lowered to 1.05 before a travel ban on January 29, according to research. “But such a value can only be reached with drastic measures – in Switzerland, we are still far from it,” says Marcel Salathé, professor of epidemiology at the EPF in Lausanne. “The last values ​​of R0 in Wuhan are estimated at 0.3”, explains Christian Althaus, epidemiologist at the University of Bern. But as soon as the current isolation measures are lifted, the infection rate could rise again.

Incubation period
The incubation period for the new coronavirus, that is, the time between infection and the onset of the first symptoms, is approximately three to seven days. However, it can last up to 14 days. On average, it is 5.5 days. If you have a viral respiratory illness, you are usually more contagious when you have the strongest symptoms. With the new coronavirus, it could be different. You can be contagious before: immediately before symptoms appear. A new study supports this hypothesis, according to which 25 to 30% of infections occur during the phase when the patient has no symptoms. WHO, however, says: although transmission of Sras-CoV-2 has been observed one to two days before the onset of the first symptoms, according to current knowledge, such transmission is rare, unlike the flu , and plays little role in its spread. It is difficult to control transmission before symptoms appear. It was different with the Sars. There, transmission was almost exclusively through people with symptoms.

Modes of transmission
Transmission is mainly by droplets: if the sick person sneezes or coughs, viruses can directly reach the mucous membranes of other people’s nose, mouth or eyes. This can happen directly from person to person via the mucous membranes or indirectly via the hands.

A study published in the Journal of the American Medical Association concludes that the new coronavirus can also be transmitted through contaminated surfaces. In the same study, in which the rooms of patients with Covid-19 were examined, there are also indications that the virus can be transmitted through stool. They found no viruses in the air.

The extent of the infection
According to epidemiologist Marc Lipsitch from Harvard University, 20 to 60% people will be infected with Sars-CoV-2. Most of his colleagues agree with him, the WHO speaks of 40 to 80%. German virologist Christian Drosten of Charity Hospital in Berlin also expects high infection rates. “Up to 70% will likely be infected, but we don’t know how soon,” he said. “It could well take two years or more.” Infection is only problematic if it occurs in a compressed and short time. Most epidemiologists assume that the virus will stay with us for the long term. Sars-CoV-2 will become established in the human population and will remain with us for the next few years. For comparison: according to the WHO, 5 to 20% of people worldwide are infected with the flu every year.

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Scenarios for Switzerland
Even if the Federal Office of Public Health (FOPH) does not want to embark on scenarios, it is part of the daily life of epidemiologists. Especially at the start of an epidemic, it is important to talk about the worst scenarios, because everyone should know what to prevent, says Marcel Salathé, professor of epidemiology at EPFL in Lausanne. Two weeks ago, he estimated the number of deaths in Switzerland at 20,000 to 35,000 in the worst case, if no action was taken. His colleague Christian Althaus of the University of Bern also made such predictions, with 30,000 deaths. “The difficulty of this calculation is that these figures can only be estimated approximately at the beginning”, explains Mr. Salathé. But if, at some point, without the vaccine or medication, you just let the Sars-Cov-2 go by without doing anything, you would expect such death numbers.

“We have no vaccine and no immunity in the population as for the seasonal flu, which however affects about 10% of the Swiss each year and kills between 500 and 2500 people in our country”, explains Mr. Salathé. “This is why it is so important to contain the spread as much as possible. But not just hoping that things go as smoothly as possible, but with real measures. In order not to overburden the health system and save time for the development of a vaccine, the increase in infections should be delayed as long as possible. ”

We have developed different scenarios for Switzerland, based on the SEIR model, which virologists use around the world to forecast the spread of infectious diseases. For variables such as infection rate, incubation time and duration of illness, we used the most recent data from the researchers studying Covid-19. Without measures, the epidemic would spread extremely quickly and peak in May. More than 100,000 people in Switzerland would fall ill at the same time. Gerhard Neher, professor at the Biozentrum at the University of Basel, has an even darker vision: “It is realistic to think that 200,000 people in Switzerland could be sick at the same time. But there are of course a lot of uncertainties in these forecasts ”.

Many will develop the disease with mild symptoms. But according to current assumptions, 10% of people will need intensive medical care. In the worst-case scenario, 10,000 hospital beds would have been needed in May – Switzerland has 40,000. Fortunately, the spread of the coronavirus can be severely curbed by meeting bans, strict hygiene rules, social distancing, etc. The number of people requiring medical assistance could be reduced by two thirds.

Marcel Salathé explained: “Maybe we can slow down the momentum because people are already staying at home and doing social distancing. As a result, the epidemic in Switzerland would progress much more slowly, and no additional drastic measures would be necessary. This would be the ideal case. But you should at least prepare yourself psychologically for this exceptional year, with fewer meetings, less travel and more home office. It’s inevitable”.

US President Donald Trump said at a meeting in the White House that the coronavirus would disappear thanks to the milder temperatures in April. “It is possible, but this analogy with the flu and the cold is still only wishful thinking,” says epidemiologist Stephen Morse of Columbia University in New York. “Let’s wait until April, then we will know if it’s true.” What we do know, however: other coronaviruses are only present in the cold season, as this study by a Swedish-Swiss research team shows. We therefore hope that Sars-CoV-2 will soon become less widespread.

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But even if it did, the seasonal nature of the virus would not stop the pandemic. As Marc Lipsitch, professor of epidemiology at Harvard University writes, a slight decrease in Sars-CoV-2 may be possible in the northern hemispheres. However, he says that it is not reasonable to hope that this will lead to a decisive decrease. An unapproved study, in which Lipsitch participated, suggests that the new coronavirus could spread in many different climates. Singapore, which is almost on the equator, is for example also affected by the epidemic.

For Richard Neher, professor at the Biozentrum of the University of Basel and expert in the propagation of viruses, it is clear: “Sars-CoV-19 will not disappear in spring and summer; at best, we can expect fewer infections. If we manage to delay the epidemic so that only a small part of the population will be infected by the summer, we will save time to prepare for a second wave in the fall. ”

Epidemiologist Marcel Salthé also sees them in the same way: “We cannot assume that the virus will simply disappear in the spring, as claimed by some politicians on the other side of the Atlantic”. The virus spreads quickly, even in countries with very different climates.

American and Chinese researchers are currently testing a drug to help the seriously ill. There is still no substance specifically developed against the new virus because it takes years. But scientists use existing drugs and see if they help fight the virus. A promising candidate is the drug Remdesivir, which has already been effective in individual cases. Researchers at the pharmaceutical company Gilead Sciences originally developed it to fight Ebola. Remdesivir sneaks into and interferes with the mechanism that RNA viruses use for replication. Both the Ebola virus and the coronavirus are RNA viruses. A 35-year-old man, seriously injured by Covid-19, was cured in Seattle. Legally, there would be no obstacle to the use of this medicine in Switzerland.

Another strategy: seriously ill patients could be treated with blood plasma from people who have overcome the disease. Antibodies from cured patients would strengthen the immune systems of newly infected patients. It has already worked with Ebola, Mers and Sras.

In addition, Norwegian researchers carried out a literature review last week to look for additional substances and reviewed 120 already approved drugs that doctors use against viruses. These include the two anti-HIV drugs Lopinavir and Ritonavir. Studies on these two drugs are also already underway in Hong Kong and Guangdong. Chinese researchers also want to test the anti-inflammatory Actemra from the Swiss pharmaceutical manufacturer Roche. It is intended to slow down inflammatory reactions.

According to the director general of the Mandial Health Organization (WHO), 20 vaccines are currently being developed to fight Sars-CoV-2. WHO has also received requests for testing and approval of 40 tests.

In mid-February, 400 experts agreed at a conference in Geneva to speed up the search for a vaccine. Many countries are currently working on a vaccine. But how fast could it be ready to use? “Overall, I am very confident that we will see the first experimental vaccines before the end of this year,” said virologist Gerd Sutter of Ludwig Maximilian University in Munich. The question of whether and when they can be tested on humans is another question. “The development of a vaccine is a long and laborious process, especially the approval and clinical trials of a candidate.”

Epidemiologist Marcel Salathé is optimistic: “I would be surprised that we do not have a vaccine by the end of the year. The situation would then return to normal next year. But for the next six months, we have to manage the coronavirus with non-pharmaceutical measures. ”

Created: 08.03.2020, 01h10

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