Coronavirus on wane in wastewater in Finland

The amount of coronavirus in wastewater has started to decline throughout the country since the beginning of August, according to the wastewater monitoring carried out by the Finnish Institute for Health and Welfare (THL).

The most recent wastewater samples were collected on 4–5 September. Based on the samples, the amount of coronavirus continued to decline in all wastewater treatment plants involved in the monitoring, with the exception of Helsinki, where the decrease plateaued.

Measured levels of coronavirus genetic material, or RNA, in wastewater have not been this low since January 2022.

The number of new laboratory-confirmed COVID-19 cases has also decreased in recent weeks.

The number of municipalities involved in coronavirus wastewater monitoring has been reduced. Going forward, monitoring will continue on a weekly basis at nine wastewater treatment plants in Espoo, Helsinki, Joensuu, Jyväskylä, Kuopio, Oulu, Tampere, Turku and Vaasa.

Additionally, samples will be collected once a month from the Lappeenranta, Pietarsaari, Rovaniemi and Seinäjoki wastewater treatment plants.

The updated weekly report published on 9 September 2022 displays both the amount of coronavirus in wastewater and the number of cases detected in the treatment plant network area since August 2020.

In addition, the amount of coronavirus RNA can be displayed either on a logarithmic scale indicating orders of magnitude or on a linear scale indicating the actual measurement value.

First wastewater observations of the BA. 2.75 subvariant of omicron in August

As viruses multiply, mutations occur in their genome. Mutations are part of the natural evolution process of viruses.

Currently, the omicron BA.4/5 subvariant is the most common coronavirus variant in Finnish wastewater.

Distinguishing between the BA.4 and BA.5 subvariants is currently not possible due to the similarity of their genomes.

The first indications of the new omicron BA.2.75 subvariant were found in Finnish wastewater on 1 August in Espoo.

The observations were confirmed in the second week of August by wastewater samples from Pori and Joensuu. The latest sequencing results are from the middle of August, when the BA.2.75 subvariant was detected again in Joensuu.

In August, indications of the subvariant have also been found in the follow-up study of laboratory-confirmed coronavirus cases.

Total proportions of different SARS-CoV-2 virus variants in Finnish wastewater found in sequenced wastewater samples from monitored wastewater treatment plants between 2 May and 15 August 2022. The paler area represents the standard deviation from the results of different treatment plants.