“In the absence of a vaccine, the best scenario we can hope for is that there is a very low rate of spread of the virus in the general population, and that if there are local hotspots and epidemics, that local health authorities can work fast enough to contain it and prevent its spread,” said Dr. Thomas Kamradt, an immunologist and professor at the University Hospital at Friedrich-Schiller University in Jena, Germany.

R number is very important?

High reproduction rates show how easily the virus spreads when left unchecked. When it falls below 1, the epidemic fades. When it is higher than 1, it spreads. If this number stays above 1 for a long period of time, there may be a point where there are more sick people than the hospital can handle. That means some patients end up losing the critical care they need – for example because there aren’t enough ventilators – and therefore the overall number of deaths is much higher.

Chancellor Angela Merkel has repeatedly stressed that in order to defeat the virus, the number – widely known as R0 or just R – must remain below 1. He suggested that new restrictions might need to be imposed if the rate rises.

But while the number R is important, it does not paint a complete picture. Levels in Germany jumped suddenly because 1,553 workers at the Toennies factory tested positive for the virus, even when other parts of the country saw very few new infections.

“R must always be seen in context,” said Marieke Degen, deputy press official at the Robert Koch Institute. “If your total infection is low – in Germany [it’s] “a few hundred per day – and some larger outbreaks, R can go up quite quickly, but this is not too problematic,” he said. It would be much worse if you had 50,000 cases daily and an estimated R of around 2 – 3. “

While the outbreak at the factory is already severe, authorities hope the virus has not been able to spread further. North-Rhine Westphalia’s Prime Minister Armin Laschet said on Tuesday that so far, only 24 people who had no connection with the factory were positive in the district. “The question is, how many people have met those who have been infected?” Laschet said at a press conference.

Detective work

Experts are now working against the clock to find out. The district has tested everyone connected to the factory, and sent 100 mobile testing teams to contact as many people as possible. A special diagnostic center has been opened in the district to ensure that anyone can get a free test. Dozens of soldiers, police officers, scientists from the Robert Koch Institute and members of the Red Cross have been mobilized to help.

Speed ​​is the most important. “You are always behind the epidemic to some extent,” said Mike Tildesley, a professor at Warwick University. “We know people can be infected for several days before symptoms appear … when you get to the stage you realize there are problems, there are already more [cases] in the population. ”

Despite great efforts, epidemiologists are careful to say the epidemic is under control. “Twenty-four seems like a low number, but it is a sign that the outbreak is not entirely limited to workers and their families … there is enough time for it to spread outside,” Dr. Martin Stuermer, a virologist and director of IMD Labor, a coronavirus testing laboratory in Frankfurt.

The Toennies factory closed last week, with all 7,000 employees and their families ordered to quarantine themselves, but the closure of the wider district and 360,000 residents was not announced until Tuesday.

Stuermer was worried that it might be too late. The German rule of thumb that was put in place when it began to reduce restrictions last month was that if an area records more than 50 new cases per 100,000 population in seven days, it should consider locking it up.

“From that point of view, it’s too late,” he said, adding that earlier serious outbreaks at meat-packing plants in Germany and elsewhere should be a warning sign. “Someone should be vigilant … Toennies start testing, they identify more and more cases, they identify herds of infections and they take steps to stop the spread, but overall, they fail to control the outbreak,” he said.

Tildesley said that compared to previous pandemics, countries such as Germany and Britain were now better equipped to prevent local outbreaks from spreading further because they had succeeded in increasing contact tracing and testing.

But both Stuermer and Kamradt say that to succeed, every part of the system must work well: Health authorities must be able to move quickly, people must respect lockouts and companies must behave responsibly.

Toennies, the company that runs the plant at the epicenter, has found itself under pressure. Clement Toennies has apologized for the outbreak and said the company assumed full responsibility, but the criticism did not stop.

CNN has repeatedly contacted Toennies to comment.

“Cooperation from the factory is not very good, the authorities have to walk there to get data about employees to be able to track them and talk to them … it can be done faster,” Kamradt said. Local officials including Laschet even suggested that Toennies should be responsible for the outbreak.

Toennies said in a statement that it was “working all the time” to help the authorities. Responding to criticism from local authorities who said the company failed to provide employee addresses, Toennies said it was not negligent and did not hide any data. It blames German data protection laws. “We are in an extreme situation and have to consider the privacy and data protection of several thousand people. In the end, we weigh the consequences and make the data available.” But federal labor minister Hubertus Heil told German tabloid Bild that he had “almost zero” confidence in the Toennies.

Many of those infected are migrant workers from Romania, Bulgaria and Poland who work in narrow conditions and on temporary contracts, with low wages. German health authorities are now trying hard to reach this previously invisible community – the district employs 150 translators to help.