From infection to pandemic: Corona took two attempts

15. September 2020 – 15:01 Clock

Previous assumptions rejected

To understand how that is Coronavirus Spread all over the world, researchers use various methods to study the onset of epidemics. With recently published study results, they throw previous assumptions for Europe and North America overboard.

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Only a renewed introduction led to the pandemic

To the Spread of the coronavirus to stop, it is important to understand chains of infection. The source of the infection is always searched for. This also applies to the global perspective. How exactly epidemics could occur in Europe and North America and what role the first Sars-CoV-2 infected people played, researchers can now say after two comprehensive studies.

The teams around Trevor Bedford from the University of Washington and Michael Worobey from the University of Arizona agree on the basis of their research results that Sars-CoV-2 could only spread massively and become epidemics in a second attempt in Europe and North America. According to the researchers, however, the first infections that were registered in Bavaria and the US state of Washington were successfully contained and finally warded off. It was only when the virus was reintroduced from China into Washington State and Lombardy that the epidemics finally brought the epidemics to Europe and North America.

Other routes of propagation

It had previously been assumed that the spread of the first two infected people, who were identified on January 19 in Washington State and on January 27 in Bavaria, started. Patient “WA1” entered the USA from China on January 15th. Patient “BavPat1” was infected by a colleague who had traveled from China. From these two patients, the virus is said to have spread uncontrolled and unnoticed by the health authorities and triggered so-called cryptic epidemics. In fact, the epidemic did not occur in the US state until six weeks later. The outbreak in Europe, specifically in Lombardy, was only around February 20, writes the German Medical Journal.

In the previous hypothesis, the virus is said to have spread from Bavaria to Lombardy and from there returned to Germany via Ischgl. Genetic similarities initially supported these assumptions. A comparison of the genes from 455 Sars-CoV-2 samples by the Bedford team confirmed this assumption at first glance. A more detailed analysis, however, showed that the virus did not arrive in Europe until February 2. This date can be calculated from the assumption of a mutation rate and the differences in the genome sequences of the viruses that were later isolated, the paper continues.

Supported by further study

The researchers, the “Seattle Flu Study”, come to similar results. In the study, a total of 10,382 airway swabs were taken between January 1 and March 15. The first positive Sars-CoV-2 test was found on February 21, more than a month after the infection in “WA1”. According to the study, the virus then spread rapidly in the period after February 21. These numbers speak against a so-called cryptic epidemic, i.e. against increased infections that went unnoticed by the health authorities.

Computer models confirm new routes of infection

Worobey’s researchers come to similar assessments. The researchers had simulated the spread of Sars-CoV-2 with the help of computer models. This, too, does not result in a uniform picture of the infection process that corresponds to the first two infected people and the later outbreaks. According to the calculations, between 140 and 2847 new infections in Bavaria had to come in the first 36 days, i.e. after January 27. It is unthinkable that so many cases would have gone unnoticed by health officials. In fact, 16 other people in Bavaria were demonstrably infected with Sars-CoV-2. In addition, the viruses that were obtained and examined from infected people in Italy were not genetically identical to those of “BavPat1”.

The results of the computer simulations suggest that the epidemic in Lombardy was triggered by a virus imported directly from China. This should have reached the region between January 20th and February 6th. This virus made it to New York about two weeks later. From here it spread all over the United States. Some of the viruses that are currently being detected in Washington State also come from this virus in Italy.

The results of both studies were published in the journal “Science”.


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