Following months of a steady decline, Finland's Covid cases have started to rise again over the past week.
The coronavirus Delta variant has also likely started to spread in Finland after hundreds of football fans returning from Russia were allowed into the country without being tested for Covid last week, according to virology professor Ilkka Julkunen.
So far, about 300 of the Finnish football tourists have tested positive for Covid-19 since their return, according to the Institute for Health and Welfare (THL).
The Delta variant — previously referred to as the variant from India — is more contagious than previous strains and is very commonly seen in Russia.
"The Delta variant spreads more easily and it will probably take over other virus strains, as it did in Britain," Julkunen told Yle TV1's breakfast news programme.
Finland needs to prevent the further spread of the outbreak, according to Julkunen and Markku Mäkijärvi, Chief Medical Officer of the Helsinki and Uusimaa Hospital District (HUS).
Both experts reiterated recent appeals by authorities and officials for the football tourists to seek out Covid tests and encouraged them to practice social distancing as well as use face masks in public.
Delta's threat in HUS area
Many of the new cases brought in from Russia were diagnosed in the HUS area. As of Tuesday, a total of 222 new cases were reported in HUS among people who returned from Russia or had been in contact with them, while 783 people have been ordered into quarantine.
"Those figures will increase even more, because not all infections have been traced in the municipalities yet," Mäkijärvi said in a HUS statement issued on Tuesday.
Health authorities became increasingly concerned about the sudden deterioration in the country's epidemic situation towards the end of last week.
Dozens of former infection chain contact tracers were called back to work, in an effort to curb new infection chains caused by the untested border crossers. At the moment, there are more than 100 infection chain trackers working in Finland.
Chief epidemiological physician at the City of Helsinki's Social Services and Health Care Division, Sanna Isosomppi, said tracking efforts were going well but the work is difficult due to incomplete information on bus passenger lists.
Furthermore, people who receive calls from contact tracers often don't answer the phone on the first try, until they are sent a text message explaining what the call was about. The process of reaching individuals by phone was particularly sluggish last week in Helsinki, Isosomppi explained.
However, the most important measure in continuing the battle against the further spread of the virus is to limit the number of people that one is in contact with, Isosomppi added. This is particularly true in the current situation, as the Delta variant is much more likely to spread than other known variants.
Don't cancel plans, use common sense
Julkunen said Finland's epidemic situation was improved by the country's vaccine coverage, as approximately 60 percent of Finland's population over the age of 16 has received at least one of two doses of a Covid vaccine.
"Two doses of the vaccine also provides quite good immune protection against the Delta variant," Julkunen said.
Meanwhile, despite the cases brought in from the east, HUS chief medical officer Mäkijärvi also said the Covid situation in Finland was good in the broader picture.
"Your summer holidays don't need to be cancelled, but we need to act sensibly and responsibly despite the fact it's summer and vacation time," he said.
Health authorities and public officials have continued to urge those who returned from Russia — as well as individuals they have been in contact with — to be tested for coronavirus infections, even if they do not have Covid symptoms.