Sublineage of Omicron variant found in Finnish wastewater

The new XBB sublineage of the Omicron variant has been found in wastewater monitoring for the coronavirus, said the Finnish Institute for Health and Welfare (THL) in a press release on Thursday.

XBB was first detected in wastewater in Espoo and Helsinki in late October and the sublineage was included in reports on wastewater analysis in December.

XBB is a recombinant sublineage of the BA.2.10.1 and BA.2.75 sublineages.

It has also been detected since late October in sequenced samples taken from humans. However, its proportion in samples does not seem to increase very fast.

Several different sublineages of the Omicron variant are now spreading in Finland. The formation of new sublineages and variants is part of the natural evolutionary process of viruses. At present there are no indications of variants or sublineages that would cause more serious illness than usual.

“The XBB and BA.2.75 sublineages descending from the BA.2 sublineage of the Omicron variant, as well as BA.4 and BA.5 sublineages can now be found in Finnish wastewater. There have been no significant changes in the relative proportions of the sublineages of the Omicron variant since July; since then, the BA.5 and the sublineages that descend from it have been the most common subvlineages found in wastewater”, said THL Senior Researcher Anssi Lipponen.

Many of the BA.5 sublineages are very similar to the main lineage and distinguishing them from each other in wastewaer samples is not possible at present.

A fairly even rising trend has been seen throughout the autumn period in the numbers of coronavirus genotypes, or RNA, in wastewater in Finland.

The most recent samples of wastewater were collected on 18-19 December 2022 and the weekly report is being published exceptionally already on Thursday 22 December.

The increase in the amount of coronavirus in wastewater indicates a typical autumn and early winter infection period that can also be seen in an increase in respiratory tract infections. There has been no corresponding rise in cases of COVID-19 confirmed by laboratory tests, because health care services are conducting only limited numbers of COVID-19 tests, for example, on members of at-risk groups for severe coronavirus disease who exhibit symptoms of the disease.

Espoo is currently taking its new wastewater treatment plant in Blominmäki into use. The results of wastewater testing the Blominmäki treatment plant will be included in the weekly report after the Christmas break.

The treatment plant will process the wastewater of about 400,000 residents in Espoo, Kauniainen, Kirkkonummi, Siuntio, and West Vantaa, which was previously processed at the Suomenoja wastewater treatment plant. The deployment of the new treatment plant means that results from the Suomenoja wastewater treatment plant will not be included in the weekly reports at the end of the year.