The COVID-19 pandemic began in late 2019 in Wuhan, China. Since then, the SARS-CoV-2 virus has spread rapidly despite attempts to restrict it. As of mid-April 2022, the number of reported coronavirus infection cases exceeded 500 million worldwide, with the total death toll over 6.2 million.

In a recently completed study, researchers from the University of Helsinki and KU Leuven in Belgium investigated the arrival and spread of SARS-CoV-2 in Finland in 2020. The results were published in the Communication Medicine log.

“Research on the geographical evolutionary history of coronaviruses revealed that in spring 2020, about 42 independent viral lineages arrived in Finland mainly from Italy, Austria and Spain. Four of these lineages caused two-thirds of the entire outbreak in Finland in spring 2020, when a single virus lineage from Spain led to a major chain of transmission that covered a third of the outbreak in the country. most of the 42 lineages did not lead to community transmission in Finland,” explains the postdoctoral researcher Ravi Kant.

“At the start of the pandemic, one of the biggest problems in monitoring chains of transmission was the genetic similarity of the virus all over the world – there were very few differences in the viral genome between countries and the chains of transmission Philippe Lemey’s research group has developed an analysis technique that combines data on human mobility at the individual and population levels with sequence analysis of the viral genome.We have applied this technique to Finnish sequencing data. says postdoctoral researcher Teemu Smura.

Coronavirus landed in Finland from Austria, Italy and Spain

According to the researchers, Austria, Spain and Italy were the most important sources of coronavirus spread in Finland in 2020. These countries also experienced the first peaks of infection in February 2020.

“A possible source of coronavirus infections are Austrian travelers who may have caught the virus at popular ski resorts. At least in the town of Ischgl in Tyrol, Austria, the coronavirus situation was severe in March 2020. The virus strains that spread from there may have been behind the chains of transmission from a number of European countries,” says doctoral researcher Phuoc Truong Nguyen.

“Our results show that only a small portion of infections are transmitted further, indicating that if travel restrictions and quarantines, testing, tracing and isolation programs, or other border control measures are deployed early enough, they can delay the development of cases of infection in extended chains of transmission in society.However, these measures will only be effective if they are combined with other preventive measures, and if the viral strains to be prevented do not have not already spread,” says Professor Olli Vapalahti.

SARS-CoV-2 has become a complex virus

The key questions relating to the coronavirus pandemic concern the continued evolution of the virus. Originally, SARS-CoV-2 spread to humans as a zoonotic disease (transmissible between animals and humans), most likely through bats.

“The circulation of the virus in a new host species requires many changes: for example, the virus must adjust its surface proteins so that they attach more effectively to the host cells. In addition, the virus must overcome the innate defenses of the host. In fact, the rapid transmission of the coronavirus between people in large human populations has produced complex genetic diversity in the virus. Currently, one of the most central questions in related research is how these different changes alter the biological characteristics of the virus, and what kind of changes selection pressure guides the virus towards in the future,” says Associate Professor Tarja Sironen.

Epidemic waves in Finland in 2020

• The first case of SARS-CoV-2 was diagnosed in Finland on January 29, 2020 in a tourist who arrived from Wuhan, China. However, the infection has not been transmitted to other people in Finland.
• The first wave of the outbreak in Finland started in late February 2020, peaking in early May and ending in early June.
• In June and July, the incidence of the coronavirus was low in Finland.
• The second epidemic wave started in August 2020 and lasted until early November.