Germany’s most famous virologist is at a loss. After returning to his highly popular German podcast after the summer holidays, Christian Drosten told his listeners that it’s "very difficult to assess” the current situation.

No one can reliably say how many people are currently infected with the coronavirus in Germany. The official number of cases reported by the Robert Koch Institute (RKI), the country’s center for disease control, could be two times lower than the true figure, or perhaps even 20 times lower. "We have to honestly admit to ourselves that we don’t actually know where the virus is right now.”

There’s only one thing that's certain: The number of coronavirus infections is rising again significantly. After lockdown measures were eased in mid-July, around 300 to 500 new cases were reported each day, but now that figure has increased to 1,300 a day, even reaching more than 2,000 on one recent occasion.

"I am very concerned about the latest developments in Germany," says RKI head Lothar Wieler. Are we witnessing the beginning of the dreaded second wave of the coronavirus in Germany? Will we soon be threatened with a new lockdown, with school closures and many other restrictions? Chancellor Merkel has also described the situation as "alarming.”

For many people, it is increasingly difficult to take these warnings seriously because there are very few people dying from coronavirus-related complications right now. There are also enough beds available in the intensive care units. Conditions like the overflowing ICU wards seen in Italy in the spring seem like the distant past.

And is the rising number of cases not simply explained by the fact that so many people have recently returned from vacation and also the fact that patients who have very few symptoms are now getting tested more regularly? Or is it possible that the virus has become less dangerous through a mutation?

"It’s a very human reaction to interpret all the signs as indicating that things could get better,” says Emma Hodcroft, an epidemiologist at the University of Basel’s Biozentrum, a center specializing in molecular and biomedical research. "But you have to be logical about it."

And the logic is clear: Studies from Britain and Spain show that the infection fatality rate of COVID-19 is 0.8 to 0.9 percent – many times higher than for influenza.

But "humans are not made to be permanently frozen in fear,” says Hodcroft. "If an exceptional situation lasts too long, we lose our fear of it. But if we let down our guard, the virus will spread again relentlessly."

Which brings us to the question: How dangerous is the situation in Germany right now? And what else is in store for the country?

1. Is the reason that we have more confirmed cases due to the fact that there is more widespread testing?

For once, Donald Trump actually is right. "Cases are going up in the U.S. because we are testing far more than any other country,” the U.S. president tweeted a few weeks back. The simple rule is, of course, true: If test for the disease, you will find the disease.

This correlation can also be observed in Germany: Whereas half a million people were being tested each week at the beginning of July, that figure had risen to 1.1 million people by the end of August, including thousands of returning vacationers. It’s no wonder that the numbers have increased since then, given that many people were tested despite showing few symptoms or none at all - cases that likely would never have gone to the doctor on their own.

But this is only half of the story. The increase in the number of cases in Germany cannot be explained by the increase in tests alone. The bottom line is that there actually are more infected people than in May or June.

An evaluation by the Robert Koch Institute shows that the number of cases is increasing much more than one would expect based on the test numbers alone. This is because the positivity rate, meaning the proportion of those tests that come back positive, has also increased. If the real number of infections were constant, however, the proportion would decrease as testing expanded.

Among 15- to 34-year-olds, the positivity rate is likely to have risen to around 1.5 percent in recent weeks. Previously, it had been less than 1 percent - a clear indication that coronavirus infections are indeed on the rise, especially among younger people.

 2. Why are so few people dying of COVID-19 in Germany right now?

Currently, the disease is generally killing fewer than 10 people per day in Germany. The situation is also similar in other European countries. Intensive care units have also largely returned to regular operations. SARS-CoV-2 seems to have lost much of its terror.

Is it possible the virus mutated during the pandemic and has become less aggressive?

"There is no indication of this,” says Hodcroft, who is researching that question in Basel as part of the Nextstrain project. German virologist Drosten has come to the same conclusion. "Overall scientific observation has not seen any change in the virus,” he has said.

What has changed conspicuously, however, is the age structure of the patients: In many countries, it is now mainly younger people who are becoming infected. In March, people aged 5 to 34 accounted for around 30 percent of cases in Germany. Now, though, they represent 60 percent of all cases. Back in April, almost 20 percent of those infected was over 80 years of age, but now, the elderly are rarely infected.

These figures provide the most important explanation for the low death rate, because the risk of dying from COVID-19 depends heavily on age. The risk of death for men over 80 is 57 times higher than it is for men between 40 and 59. Compared to 20 to 39-year-olds, the risk of death among the elderly is even 644 times higher.

There is no certainty that younger people will continue to represent the highest number of infections in the coming weeks and months, even if many older people are showing extreme caution and avoiding social outings to the extent possible. The experience from the spring shows us that when young people party, work, travel and get infected that, at some point, the virus will travel to the elderly as well.

"Older people will ultimately become infected, because families do eventually meet, which is why the virus won't just remain among the young," says Drosten.

"It's a gamble," explains Hodcroft. "The more the number of cases increases, the greater the likelihood that we will once again be seeing more elderly people becoming infected. The same thing happened in Sweden, despite the deliberate efforts made to shield the elderly."

In Spain, where the number of infected persons has been dangerously high again for several weeks now, the number of deaths is also rising again.

And in Florida, relief that the virus had possibly become less terrifying was fleeting, and soon more and more elderly were getting infected, with many deaths. "We have to do everything we can to keep case numbers as low as possible," says Hodcroft.

3. At what point does the pandemic spin out of control?

If you take a closer look at the situation in France, you can guess what German epidemiologists and politicians are afraid of.

For three months, the number of infections in Germany’s neighboring country remained at a low level, but they exploded in August. More than 7,000 cases are now being reported a day, with even more than 15,000 on some days. It appears that France has already crossed the point at which it is impossible to contain it.

In fact, there could be a critical threshold above which the infection processes get out of control, even if no one is able to say yet where, exactly, that value lies.

What is happening in countries like France and Spain could have to do with a phenomenon known in physics: "percolation.” It describes, for example, how electrical conductivity suddenly increases when the metal content in a metal-glass mixture exceeds a certain threshold.

Epidemiologists use this model to better understand how infectious diseases spread. "During the lockdown in France, a low contact rate and low mobility ensured that local outbreaks remained small,” says mathematician Pieter Trapman of Stockholm University. He has used the phenomenon of percolation to explain, for example, the transmission of the plague pathogen between gerbil families.

According to the model, the infections initially simmer in isolated clusters, and the virus only rarely jumps from one group to another.

If, after the end of a lockdown, the infections and also the contacts between people slowly increase, not much will change in terms of the course of the infections. There will be more cases in the clusters, but the outbreaks remain local. Epidemiologists are hoping for this to be the current situation in Germany.

But when people start moving around more, have increased social contacts and the infection rate continues to rise, chains of infection develop between groups that are actually separate from one another - and the virus suddenly spreads uncontrollably.

Virologist Drosten is also worried that percolation is playing an important role in the coronavirus pandemic. "I have known for years that this phenomenon exists,” he says.

The model shows that the epidemic situation can suddenly spiral out of control. And why does it appear that this has already happened in France?

Drosten attributes this to the fact that the number of infections in the spring was significantly higher there than in Germany. "I think we are still below a percolation threshold in Germany, but France and Spain may already have exceeded it.” The fact that the countries didn’t begin their lockdowns until later in the spring means that they may have "more infection mass in the background.”

4. Are fewer people dying from COVID-19 because better treatments are now available?

Most experts doubt that a sufficiently effective vaccine will be available this winter. However, considerable progress has been made in the medical profession in treating the sick.

Of the many medications that were tested on the new coronavirus all around the world in the first few months, three in particular have actually proven successful: anticoagulants, dexamethasone to suppress an excessive immune response, and the drug Remdesivir, which inhibits the replication of the virus. "We now have a much better feel for this disease,” says Marius Hoeper, acting director of the Department of Pneumology at the Hannover Medical School.

Torsten Feldt, the senior physician at the Institute for Tropical Medicine at Düsseldorf’s University Hospital, is also cautiously optimistic. "I would definitely not give the all-clear," he says. "I'm sure we'll have another critical period in the fall and winter." And despite better treatment options, he says patients under 50 will still die. "We can't stop that yet. But now we know what to do – we are prepared for almost all scenarios. I don’t think the situation in the hospitals will get out of control so easily.”