Chancellor Angela Merkel recommended spending the autumn holidays last week in Germany – or in European regions with low contamination rates, such as Italy. Just a few days later, it doesn’t seem so easy for Berliners to plan anymore: People coming from coronavirus-risk areas in Germany must be quarantined for 14 days in Schleswig-Holstein – this now also applies to residents of Berlin’s Mitte, Neukölln and Friedrichshain-Kreuzberg.
Decisive for this classification are the figures of the Robert Koch Institute (RKI), how many of the 100,000 people in the individual neighborhoods, boroughs and Berlin districts are infected with the corona virus within seven days: If this value is higher than 50 they are considered risk areas. According to his own counts of the daily mirror, which evaluates the reports of the health authorities slightly faster than the RKI, Tempelhof-Schöneberg and Charlottenburg-Wilmersdorf also sometimes exceeded the value of 50 at the weekend. The federal states draw very different consequences from the figures : Berlin and Rhineland-Palatinate, for example, only lifted the quarantine requirement for people from risk areas over the weekend.
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In addition to reminders about protective measures against the virus, politicians and doctors repeatedly explain that another strict lockdown and curfew are unlikely to be necessary – RKI president Lothar Wieler also believes the situation is manageable and said he used the S-Bahn every day. in Berlin.
Before the latest meeting, the Prime Minister of North Rhine-Westphalia, Armin Laschet (CDU), asked the federal government and the states to take into account not only the number of new infections for risk assessment, but also based on the hospital’s capacity, the share of traceable infections and the percentage of positive results from all tests to develop a uniform traffic light model, as Berlin and Austria already use. However, the federal and state governments initially only agreed to establish “an appropriate early warning system” that should help prevent the 50 seven-day incidence rate being exceeded.
Which indicators are suitable for an early warning system?
The basis of all important values and calculations – including the so-called reproduction value and doubling time – is the number of newly infected people who tested positive for Sars-CoV-2, which health authorities report daily. However, the decisive factor in assessing the dynamics of the pandemic and when it threatens to get out of control is how quickly more and more infected people are in a region. “All other indicators are related to a delay, for example hospital admissions or R-value estimates,” says Mirjam Kretschmar, scientific director of mathematical disease modeling at Utrecht University.
The doubling time, which indicates the period of time in which the number of new infections doubles, is useful in case of a strong infection. In Germany it is currently 90 days – but only 45 for Berlin.
The pandemic gets “out of control” long before the clinics fill up: when health authorities can no longer adequately monitor and isolate the contacts of infected people. Kai Nagel, mobility researcher at the Technical University of Berlin, believes this has been neglected in the discussion so far. In the “Modus-Covid” project – “Model-based research of school closures and other measures to contain Covid-19” – the physicist uses his computer models to protect against infection: they simulate the movements and contacts of people in buses and trains , at work or in schools. The crucial question is when health authorities are overwhelmed by identifying the contacts of the people identified as infected within one day and quarantining them.
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There is no unambiguous, generally applicable limit for this, as this is also related to the facilities and organizational structure of the government. But Nagel estimates that health authorities will be overwhelmed when the previous limit of 50 new infections per 100,000 residents in seven days for political action is reached. Converted, this means that the Berlin offices per day, cautiously estimated, about 250 new cases arise. Experience has shown that each of them had between 10 and 100 contacts in the contagious phase of their disease. “That means health authorities have exactly one day to reach these 2,500 to 25,000 contacts and order quarantine, because the next day they have to find the next 2,500 to 25,000 contacts,” Nagel says. “That sounds like a lot to me and I don’t think it is possible.” If the contacts are not reached in time, infected people will infect others.
Then the R-value, the measure of the number of people infected by an infected person, increases and the number of new infections increases exponentially. Then you can ‘only take countermeasures with relatively drastic restrictions’, says Nagel. The use or imminent overload of contact tracking would be an indicator of early action to be taken. To do this, you need to measure how fast, on average, health authorities reach each contact of an infected person in their contagious phase. If that takes several days, contact tracking will stop working. This makes it clear that politically ordered contact restrictions are not only intended to minimize the direct risk of infection, but also serve to track contacts more easily.
The capacities of the test laboratories could also serve as an early warning system, says Nagel: “The laboratories should not be fully utilized, otherwise tests will be postponed until the next day and we will soon have the same problem.”
Are hospital admissions and death rates of sick people a sensible criterion?
“That’s just too late”, says Nagel: “When it comes to keeping the number of infections under control, you can’t wait until the hospitals are half full before you take action.” Rafael Mikolajczyk, director of the Institute of Medical Epidemiology at the University of Halle-Wittenberg also says: The capacity of intensive care beds is “only of theoretical importance, as the overload of the health system is preceded by the loss of control over the epidemic. “, and control should start earlier” Limiting meeting larger groups (especially when unfamiliar people meet), extending mask requirement, better adherence to distances and ventilation recommendations. “
Which early measures prevent more drastic measures?
Nagel believes that using the Bundeswehr to track contacts is both possible and useful. “But people must of course be trained, and already now.” Another possibility would be a “cluster strategy” for contact tracking, as suggested by Charité virologist Christian Drosten. Because Sars-CoV-2 is mainly spread via superspreading events: 80 percent of the secondary infected are infected by less than ten percent of the infected. In other words, most infected people don’t infect anyone, but a few dozen, causing clusters of infections. The key figure for this is the dispersion value “k”: the smaller “k”, the more strongly a pathogen spreads via super spreaders. In influenza it is 1, so hardly superspread, Sars-CoV-2 has a “k” of 0.1, estimates a research team led by Sebastian Funk of the London School of Hygiene. According to Drosten, health authorities overwhelmed with follow-up should focus on these cases as needed.
When are drastic measures like curfews necessary?
“Hopefully that is not necessary,” says Nagel. “In our simulations we consistently find that a complete shutdown is not much better than a targeted dilution of human density.” For example, closing a school doesn’t mean much less contact than if the students wear masks, are often ventilated and alternate face-to-face teaching and homeschooling so that only half of the teachers and students meet. “Of course these are just model calculations, but we are pretty sure of that,” says Nagel. The same applies to offices: as long as a mask is worn on the work floor, open office spaces are well ventilated and some of the employees remain in the home office, this is sufficient. “For the areas of education and training, work, public transport and fresh air leisure events, there is a catalog of measures that can be used to minimize the contribution to contamination,” says Nagel.
Nagel mainly sees problems in restaurants, cafes and bars, family celebrations and mutual visits, such as “dinners”. It’s not so much about the number of people, but about the density – how many people per square meter come close. You can enforce such rules in restaurants, but in private you can do nothing but appeal: “No more than six people in a living room of 30 square meters.”
In the current report of the “Modus” project, Nagel emphasizes that the protective measures “do not have a linear effect”: “As many measures as possible that may not be implemented perfectly