Omicron subvariants most common in wastewater in Finland

BA.4/BA.5 subvariants of the Omicron coronavirus variant are now more common than the BA.2 subvariant in Finland, according to the results of wastewater monitoring carried out by the Finnish Institute for Health and Welfare (THL).

The relative proportion of mutations indicating subvariants BA.4 and BA.5 exceeded the proportion of the BA.2 subvariant in wastewaters at monitoring locations around midsummer.

Around the same time, BA.4/.5 subvariants also became the dominant virus in nationwide variant sequencing of that covers a sub-sample of laboratory-confirmed COVID-19 patient samples.

Wastewater monitoring investigates the total amount of coronavirus genetic material (RNA) and the proportions of different coronavirus variants in Finnish wastewater.

The RNA number has remained at a high level in wastewater, which means that a large number of infections is still circulating among the population.

As a major share of the infections are only verified by home testing, laboratory-confirmed cases do not reflect this situation.

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

Omicron BA.4/5 subvariants were detected in Finnish wastewaters for the first time in Kuopio on 8–9 May 2022. By the end May, these subvariants were already detected in the wastewaters of ten different monitoring locations.

The most recently completed sequencing results are from wastewater samples collected in mid-July 2022, at which time the latest subvariants were dominant at all locations covered by THL’s wastewater monitoring.