Grampians Health made the announcement after Omicron strains BA.4/BA.5 were identified at wastewater treatment plants in the Wimmera and Yarriambiack catchment areas.

While it is too soon to detect a local trend, the increase in wastewater detections indicates the new strains were also prevalent at a higher rate in the community.

This trend is being seen statewide, with detections of the BA.4/BA.5 strain in Melbourne and regional wastewater catchments increasing to 12 per cent, up from 4 per cent on May 21.

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While there is no evidence that BA.4/BA.5 causes more serious disease, there is a correlation with increased overall cases, hospitalisations and deaths.

"The more people who become unwell, the more likely it is that our hospitals are going to see continued increases in patients with COVID-19 needing care." said Dr Rob Grenfell, chief strategies and regions Grampians Health.

Dr Grenfell reminded residents to continue vaccinating and urged anyone eligible for their third or fourth dose to get it as soon as possible.

"We can keep each other safe by staying up to date with vaccinations, isolating for the full seven days if we are COVID positive and staying home if we are unwell," he said.

"As winter is here, it's important we keep doing all the simple things that keep us safe. It will keep the pressure off our local hospitals and health workers, who are already stretched, and help those in our community who are more at risk of serious illness or death if they do get COVID."

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Dr Grenfell said many workplaces and health services are dealing with workforce pressures due to COVID and influenza, forcing staff to miss work.

"Thank you for having your vaccine because that has certainly reduced the number of people we've had in hospital and has saved many lives," he said.

The Omicron BA.2 strain remains the dominant variant in Victoria, while the BA.2.12.1 strain continues to be detected at low levels.

Face masks are still required for everyone aged eight and above in some locations, including on public transport, rideshares and taxis, and in sensitive settings such as hospitals and care facilities.

They are also required by household contacts in quarantine who meet the criteria for leaving home.

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Masks are strongly recommended in shared indoor settings; if you can't physically distance; or you are with those more vulnerable to COVID-19.

Improve ventilation by opening doors and windows, using fans or purifiers, and gathering outside where possible.

COVID-19 early treatments are now available for eligible Victorians who are at higher risk of developing a serious illness with COVID-19 infection.

More information can be found via www.grampianshealth.org.au.

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