When will the curve finally flatten out?

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When will the curve finally flatten out?


We sit at home, staring at the thousands of new infections that are reported every day, and ask ourselves: When will social distancing finally be effective?



© Image: Ina Fassbender / AFP / Getty Images, graphic: ZEIT ONLINE, [M] TIME ONLINE
The curve of new infections is still fluctuating strongly. But it could show in a few days whether the measures taken will work.


For almost two weeks now people have not been able to go to yoga or the bouldering hall, they no longer meet friends for a beer, and they do not see their grandchildren on weekends. The work takes place at the kitchen table, where you nervously try to survive the video conference with the boss without one of the children screaming through the picture. Anyone who has to do without a lot and have to put up with such a difficult situation naturally wants to know: does all of this pay off? When will the curve of new corona infections finally flatten?

A look at the numbers unfortunately does not provide a clear picture: since March 26, new infections have actually decreased slightly in Germany – but only for four days, then the curve rose again more steeply. Depending on how optimistically one interprets these numbers, the developments can be interpreted in two directions: The small hollow that formed at the beginning of last week could indicate that the whole measure – the social distancing, the closure of day-care centers, schools, shops and restaurants, the constant washing of hands and keeping your distance – have a first effect. But you could also look at the renewed increase in the curve since the middle of last week and conclude that the measures taken are of no use.

The honest answer is: the development cannot yet be reliably interpreted. However, that could change soon. “Every day we get more security,” says Rafael Mikolajczyk. However, the head of the Institute for Medical Epidemiology, Biometry and Computer Science at Martin Luther University Halle-Wittenberg advises: “I would give us a few more days until we can see a clear trend.” It can take a long time for the corona virus to be reflected in the data, and there are several reasons for this.

A central factor for the reliable assessment of the Sars-CoV-2 virus is the incubation period, i.e. the time between the infection and the appearance of the first symptoms. This period of time is unusually long with the new corona virus. On average, infected people start coughing, fevering, or other symptoms after five to six days. In individual cases, the incubation period can be 14 days or even longer (Journal of Clinical Medicine: Linton et al., 2020). At the moment, people in Germany are mostly tested for the pathogen who already have clear symptoms. This means that the graphics lag behind, they show the number of people who got infected five days ago – possibly even earlier.

Assuming an infected person is tested, as soon as they experience symptoms, it takes a while for the sample to be examined in the laboratory and a test result to be available. According to the Robert Koch Institute (RKI), it can take six to ten days from infection to get a positive test result. Then the health department has yet to pass on the numbers of infected people to the state authorities. From there, in turn, the nationwide responsible RKI informed. Only then do the positively tested appear in the national statistics. If you also consider the closure of some authorities on the weekends, the curve can flatten out quickly, with no actual decrease in new infections.

The delays due to the incubation period and the reporting system contribute to the fact that the graphics cannot reflect the current situation of the pandemic. “If you count the cases every day during an epidemic, they reflect the prevalence and risk of at least two weeks ago,” said Michael Ryan, director of the Health Emergency Program at the World Health Organization (WHO).

It is therefore not yet possible to assess how effective the measures taken so far are. That also has to do with it, says epidemiologist Mikolajczyk, that the initial restrictions specifically aim to minimize social contacts outside of one’s own household. People are still in contact with the family or roommates. One must therefore bear in mind that many household members will first become infected with the infected before a clear flattening of the curve can be seen. “Therefore, the measures may be more effective than they look in the short term.”

If one relies on the statements of the WHO director Ryan, measures such as exit restrictions, daycare and school closings and the home office show an initial effect after two weeks at the earliest. Angela Merkel’s address to the Germans has been around that long. The Chancellor asked the population on March 18 to keep their distance. So the impact of the speech would only just start to be reflected in the numbers.

But even if this were the case, this interpretation should also be viewed with caution. The data situation is difficult because too many factors affect whether the curve becomes steeper or flatter. The way you test can significantly distort the number of cases. Statisticians speak of a bias. The more tested, the more infected people are found.

Especially at the beginning of the epidemic, laboratories, hospitals and health departments gradually increased their capacities. However, if the number of tests is increased rapidly, the daily number of confirmed infections can increase even faster than the number of those who actually got infected that day. Because the infected people who could not get a test on the previous days are tested – if at all – afterwards and therefore do not appear in the statistics until much later or not at all. Conversely, if the number of tests stops increasing, although the infections continue to increase, the increase will slow down, for example because the laboratory capacity has been reached.

In order to be able to reliably assess how the contact block affects the number of new infections, the authorities would have to test the same amount consistently. In the reality of a pandemic that also hits Germany somewhat unprepared, this is an unrealistic requirement. Also in Wuhan, where the new corona virus first appeared at the end of 2019, the numbers have been fluctuating up and down for a while after the strict lockdown, says Michael Ryan of the WHO. This is not least due to the fact that China has changed its way of counting several times.

In recent days, the RKI has also made various recommendations as to who should be tested and who should not. Such changes are reflected in the number of cases. “It would not only be important to document how many tests take place, but also in what context they are carried out,” says Mikolajczyk from the University Hospital Halle (Saale). But the number of tests has not been documented in Germany for a long time. In the meantime, the RKI is reporting how many tests were carried out in Germany per week.

It is difficult to interpret the numbers clearly. But at least they show a tendency. But we should still enjoy this with caution at the present time. “It is still too early to judge whether there is a lasting effect,” says Richard Neher from the Biozentrum at the University of Basel. In addition, flattening the curve is not enough. Because even if the measures led to the number of new infections remaining constant, that would not be enough to curb the epidemic. “The number of cases has to go down!”

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