Infection Protection Act: How meaningful is the incidence value?

REUTERS / Andreas Gebert

Changes to the Infection Protection Act will be voted on this Wednesday in the Bundestag and Bundesrat in a fast-track process. The law should now also include the measures against the pandemic that the federal government has so far enforced through ordinances, such as the mask requirement, the ban on events or the closing of restaurants and shops. You can find the draft law here.

The planned new Infection Protection Act is also criticized – by scientists, among others. Because it also sets the incidence value of 50 new infections per 100,000 inhabitants in the past seven days. From this limit value “serious protective measures” should be able to be taken, from a value of 35 “strongly restrictive protective measures” and with a value below that “simple protective measures”.

The value of 50 was seen by the federal government in the spring as an overload limit for the health authorities, above which control over the infection process can be lost. According to the Robert Koch Institute, the incidence value is currently far higher throughout Germany, at 141.

Statistics experts criticize: the incidence value alone is insufficiently informative

But the incidence value depends on many factors that can limit its informative value for the course of the pandemic. Statistics experts, for example, pointed out in a message from the RWI Leibniz Institute for Economic Research in Essen at the end of October. Because the absolute number of new infections must also be set in relation to the number of tests. Since the test capacities were still significantly limited in the spring, the figures for the first wave from March and April cannot be compared with those from September or October.

Because at that time, many people were tested who showed clear symptoms and thus had a high probability of getting seriously ill with Covid-19. Since the summer, however, there have been increasing numbers of mass tests on younger population groups who are less likely to become seriously ill, such as those returning to travel and certain professionals. According to the Robert Koch Institute, infected people were on average 32 years old in August. In April this value was still more than 50 years.

However, the rate of positive tests has risen significantly since September and is currently just under ten percent. As in the spring, the probability is increasing again that infections will not be recorded due to a lack of test capacities. The mean age of those infected has also risen continuously since August. And the number of deaths has been rising again since the end of September. On Tuesday, 305 coronavirus-related deaths were reported to the Robert Koch Institute.

“A value of 50 cases per 100,000 inhabitants today has a completely different meaning than six months ago”

Nevertheless, the ratio of the deceased to those infected two weeks earlier has fallen significantly, write the scientists, who also include the Berlin psychologist Gerd Gigerenzer and the statistics expert Katharina Schüller. In all age groups it can be seen that the proportion of those who have died has decreased significantly since spring. Two studies from the USA and Great Britain come to similar results. One reason for this could be that doctors, nurses and hospitals are now much better prepared for severe cases of Covid-19.

“A value of 50 cases per 100,000 inhabitants today has a completely different meaning than it did six months ago,” write the statistics experts in the message from RWI Essen. “The only case where one could justify looking only at the 7-day incidence is whether health officials can still track the number of contacts for people with positive tests. In all other cases, we urgently advise not only to consider the change in the 7-day incidence compared to the ‘first wave’, but also the change in positive test rates and death rates or the proportion of corona patients in intensive care units . ”

“The sole reduction of the situation assessment to a single measured value, as provided here, cannot be justified epidemiologically and does not correspond to the state of the available scientific evidence,” said epidemiologist Gérard Krause from the Helmholtz Center for Infection Research in a statement as an expert on the draft law.

The load limit of the health authorities could, for example, also be positively influenced by improved digitization and staffing. Krause also points out that the number of cases reported alone does not sufficiently express the severity of the pandemic situation. For example, changed test strategies and case definitions or the introduction of new test procedures could lead to very different reporting figures. “This indicator therefore does not have the robustness required to justify appropriate measures depending on it.”

The SPD health expert and epidemiologist Karl Lauterbach sees it differently. In the past few months it has been learned that the incidence value is helpful and useful as an epidemiological guide. “From a 7-day incidence of over 50, we are usually already in exponential growth,” he told the “Spiegel”. “Then contacts are very difficult to trace and the probability of superspreading events increases sharply.”

The virus cannot be isolated from a specific population group. Therefore, the risk groups could only be protected by influencing the value of new infections in the general population.



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