Corona has long been shaping our streetscape (here passers-by in Bonn): "If we keep the degree of contact reduction as in the current partial shutdown, the number of new infections every day will remain at around 20,000"
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We have to learn to live with the coronavirus.
The sentence comes up again and again in the Sars-CoV-2 pandemic, but the question of how exactly this could succeed has so far largely remained unanswered.
Researchers working with physicist Viola Priesemann from the Max Planck Institute for Dynamics and Self-Organization took a closer look at two concepts and calculated what they would mean for each individual and the longer-term course of the pandemic.
Two long term options
Priesemann specializes in simulating spreading processes - such as that of viruses.
"No vaccination has yet been approved and it will take time to distribute the vaccine to the population," she said on Wednesday in an interview with journalists.
"So now we have to think about which strategy makes sense for the next few months."
Two concepts in particular are being discussed: It is conceivable to focus on keeping the number of infections and ultimately the number of patients who have to be treated in intensive care units below the capacity limit of the clinics.
The alternative would be to keep pushing the numbers so far that reliable contact tracking is possible.
The calculations by Priesemann's team point in a clear direction: once the number of new infections has been reduced to around a thousand a day, people would only have to restrict their contacts a little in order to contain the virus in the long term, reports the explorers.
Restaurants and cafes could then reopen with hygiene concepts.
On the other hand, consistently high numbers of infections meant sustained major restrictions in order to just prevent overcrowding of the intensive care units.
At the same time there would be more sick people and more dead people.
Fewer sick people, fewer dead people, more freedom
When the number of cases is low, it is sufficient to prevent 40 percent of the infections in order to stabilize the spread of the virus and prevent a further, nationwide shutdown, the researchers write in their previously published study.
Since infections arise through contact, this means that people also have to reduce encounters with others by 40 percent compared to the time before the pandemic.
According to the scientists, this can already be achieved through relatively mild contact restrictions.
According to a study, limiting the number of participants in major events to one hundred people would mean that there would be around 35 percent fewer infections in the population.
If you reduce the group size to less than ten, you will achieve around 45 percent reduction.
Frequent ventilation, keeping your distance and wearing a mask can also reduce the risk of infection, so that more contact would otherwise be possible.
"In the scenario, people would only have to forego comparatively few contacts and otherwise would have great freedom," said Priesemann.
At the same time, the number of sick people and thus deaths would fall significantly.
The economic consequences would also be less if catering establishments could reopen.
One last tough shutdown
However, a final hard shutdown would be necessary in order to reduce the numbers so far that the virus can be controlled again.
"So many people are currently infected that the health authorities are unable to identify and isolate infected people before they infect other people," said Priesemann.
In addition, around ten percent of the tests carried out are positive.
This high value is a clear indication that the test capacities are not sufficient to check all and therefore more unfounded suspected cases.
"That means there is a high number of unreported cases and with it many chains of infection that cannot be contained at all."
The aim must therefore be to push the R-value back below 0.7, as was the case in the first wave, according to the researcher.
This could cut the number of infections at least in half every week.
"Just as we see exponential growth with an R value above one, the numbers decrease exponentially with an R value below one."
The effect is reinforced by the fact that fewer cases are overlooked with lower numbers of infections.
If there are few new infections, rapid tests could also make it easier to control the infection process in the future, explained Priesemann.
Protection against superspreading at Christmas
If, with the help of the measures now decided by the heads of state of the federal states and Chancellor Angela Merkel, the number of infections could be reduced by an additional 30 percent, the number of new infections in the period from December 1 to Christmas could be reduced to around 2500 - and would then be relatively easy to control.
An extra week could reduce the value to around a thousand.
To be able to do this by Christmas, around a third of the current infections would have to be prevented from now on.
"Christmas parties with ten people from different households and their children, as well as New Year's Eve celebrations with low numbers of infections with regular ventilation, could easily be justified," says Priesemann.
The probability of meeting an infected person at one of these events is low under the conditions mentioned.
In addition, chains of infection that started on the holidays could be contained more easily (read more about this here).
If the infection situation got out of control again in a region, countermeasures would have to be taken quickly in a small area.
Infections that would be brought in from neighboring countries could to a certain extent be contained through contact tracing, said Priesemann.
"The best thing would be a uniform strategy with the clear goal of low case numbers across Europe."
Noticeably reduce contacts in the long run
The alternative concept of reducing the number of infections just enough so that the intensive care capacities are sufficient would, according to the study, mean maintaining the current situation more or less permanently.
Occasionally, hospitals are already reporting overloads.
There are still options to switch to other clinics, but the scope is getting smaller.
"The restrictions of the past few weeks have resulted in the R-value falling from around 1.4 to around one," explained Priesemann.
This means that each infected person is currently infecting another person on average.
"If we keep the degree of contact reduction as in the current partial shutdown, the number of new infections every day will remain at around 20,000," says the expert.
The numbers would rise again through easing.
According to the researchers' calculations, if the incidence is high, infections and thus contacts must be permanently reduced by around 60 percent compared to the time before the pandemic, otherwise nationwide shutdown measures would be necessary repeatedly.
While four out of ten infections and thus contacts would have to be eliminated with low numbers of infections, here it is six out of ten.
»The 40 percent reduction in contact in the low-incidence scenario can be achieved almost solely by avoiding large events and larger meetings and through hygiene measures.
To forego an additional 20 percent of the contacts makes it necessary to also cancel significantly smaller meetings - and even that might just be enough, «explained Priesemann.
A communication problem
Side effects of this strategy would be, in addition to the permanently stronger contact restrictions, higher sickness and death rates and thus a higher burden on the health system as well as tens of thousands of people in quarantine.
"That is also a disadvantage for the economy," said Priesemann.
In addition, the strategy is riskier, since the long-term consequences of a Sars-CoV-2 infection are still largely unknown.
However, Priesemann also sees a difficulty in the low-incidence scenario: "It is more difficult to communicate this model in a comprehensible manner, because contact tracking is a more abstract criterion than overcrowded intensive care units."
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