It is called the prevention paradox: precisely because preventive measures are effective, there is no evidence of their effectiveness. This raises doubts as to whether the countermeasures – as in the current case of the corona shutdown – were necessary at all. A team of researchers has therefore checked whether and what the individual measures against the corona pandemic have brought here. The result: In the case numbers and the spread of Sars-CoV-2, three stages of the decrease can be seen – and these coincide fairly exactly with the entry into force of the three packages of measures in Germany.
Italy and Spain were the deterrent examples: They experienced such rapid increases in the number of cases of Covid 19 at the beginning of the corona pandemic that it overwhelmed clinics and the health system. The drastic scenes from Italian hospitals led to concerns about such an escalation also growing in Germany. For this reason, among other things, the federal government – like the governments of other countries before – decided to largely lockdown: schools and shops were closed, events were banned and exit restrictions and contact restrictions were imposed. In the meantime, many of these measures have been relaxed and the large wave of Covid cases did not occur in Germany. However, this now raises doubts in some people as to whether the hard measures were necessary at all: would the epidemic possibly have been less dramatic than it was initially postulated?
Looking back at epidemic development
Scientists call these doubts a prevention paradox: precisely because preventive measures are effective, there is no evidence of their effectiveness. Because the consequences feared without these measures are missing. This usually makes it difficult to prove in retrospect that the incisions were necessary and effective. However, in the case of the corona epidemic, there is a way for us in Germany to check the effectiveness of the measures on the course of the epidemic: Because public life has been shut down in three chronologically separate steps, you can see for each of these packages of measures whether it has an impact on the transmission rate and the number of new infections. This is exactly what researchers led by Jonas Dehning from the Max Planck Institute for Dynamics and Self-Organization in Göttingen have now investigated.
For their study, the scientists evaluated the Covid-19 case numbers in Germany and compared the spread of the coronavirus Sars-CoV-2 in four phases of the epidemic: Before the measures began, after the cancellation of large public events around March 8, 2020, after the closure of educational institutions and many shops on March 16 and after the extensive ban on contacts on March 22. They calculated that new infections are usually only reported with a delay of a week, because the symptoms only appear after five to six days and then again up to three days before the test result. Using an epidemiological model, the researchers determined the rate of spread of the coronavirus in the form of several indicators, including the rate of reproduction and the rate of growth. The growth rate indicates the number of new infections minus the number of those recovered. “If the effective growth rate is greater than zero, the number of cases increases exponentially, it is less than zero, recovery dominates and new cases decline,” explains Dehning and his team.
Three cuts can be seen
The evaluations gave clear indications of a connection between measures and epidemic development in Germany: “We have found clear evidence for three points of change in the course of the epidemic,” the researchers report. The first of these turning points occurred around March 7, 2020 and halved the growth rate. “This date coincides with the timing of the first government measures, which included the cancellation of major events, but also with the increased vigilance of the population,” report Dehning and his team. The second stage in the case numbers followed around March 16. “This second change point matches the timing of the second package of measures, which closed schools and some stores,” the researchers said. These measures brought the growth rate down to just slightly above zero.
According to the data, the third cut occurred on March 24. “This date matches the entry into force of the third package of measures with the closure of contacts and the closing of all non-essential stores,” said Dehning and his team. “Only after this third intervention did the mean growth rate drop below zero and thus indicate a decrease in new infections.” According to the scientists, the course of the epidemic in Germany clearly shows that the containment measures had a concrete, understandable effect. “After each of these measures and the corresponding change in behavior of the population, we noticed a significant reduction in the rate of spread,” said Dehning and his team. “However, our results also show that the full extent of the measures was necessary to stop the exponential growth.” How the virus spread and the Covid 19 case numbers will develop in the course of the easing is still unclear. “We have only recently seen the first effects of the easing on April 20 in the case numbers,” explains Dehning’s colleague Michael Wilczek. “And until we can evaluate the easing of May 11th, we also have to wait two to three weeks.”
Source: Jonas Dehning (Max Planck Institute for Dynamics and Self-Organization, Göttingen) et al., Science, doi: 10.1126 / science.abb9789
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