Minnesota has reopened free COVID-19 testing sites in St. Paul and Bloomington this week — only two months after shutting down sites in both cities amid optimistic signs that the pandemic was fading.

A highly infectious delta variant of the coronavirus has sparked a new wave of COVID-19 cases since that time, prompting renewed demand for testing in order to diagnosis illnesses and chart the spread of the pandemic.

"Combined with social distancing, masking, and staying home when sick, testing can help us slow the spread of the delta variant as we continue to get as many folks vaccinated as possible," said State Health Commissioner Jan Malcolm in a statement.

The positivity rate of COVID-19 diagnostic testing had dropped from a peak of 7.5% in early April during the prior wave to a low of 1.1% on June 28. It has since risen to 6.6%, back above Minnesota's caution threshold of 5% that indicates substantial viral spread.

Testing resumed at Roy Wilkins Auditorium in St. Paul on Tuesday, and will be available each week from 11 a.m. to 6 p.m. Monday through Thursday, and then from 11 a.m. to 4 p.m. on Sundays. Testing resumed Monday in Bloomington at a former Department of Motor Vehicles facility, and will be available from 11 a.m. to 6 p.m. on weekdays.

Pop-up testing sites also are being relocated in Mankato and St. Cloud later this week to meet ongoing demand. The weekly testing rate in Minnesota has tripled since early July. Minnesota's pop-up sites offer a saliva test through a state contract with Vault Health.

More than 70% of eligible people 12 and older in Minnesota have received at least first doses of COVID-19 vaccine, which has shown in studies to offer strong protection against severe illnesses and hospitalizations. However, the vaccines appear less effective against the delta variant in preventing all infections, including mild and asymptomatic cases, raising the need for testing and other strategies to manage the spread of the virus.

The state's list of community testing sites includes locations in Winona, Moorhead, Duluth and Brooklyn Park.