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All of the foreboding trends that prompted the World Health Organization to declare COVID-19 a global pandemic exactly two years ago are declining in Minnesota.

COVID-19 hospitalizations in Minnesota declined Thursday to 313, the lowest total since Aug. 7 and below the peak of 1,629 on Jan. 14. Positive COVID-19 tests dropped to 3.7% of the total in the week ending March 3, despite a decline in testing activity.

New outbreaks of at least five pre-K-12 students or staff found infectious in school dropped from 816 in mid-January to as few as four in the two weeks ending March 5, according to a Minnesota Department of Health update Thursday.

All of which has health officials asking the hopeful question: When will the pandemic no longer be a pandemic? Epidemiologists are studying when COVID-19 should be redefined as endemic, in which infectious disease levels are constant but manageable, said Dr. Jack O'Horo, an infectious disease expert with Mayo Clinic.

"The fortunate thing right now is we are continuing to see numbers fall as we approach this new normal," he said.

COVID-19 levels have been declining since mid-January in Minnesota, which on Friday recorded another nine COVID-19 deaths and 583 coronavirus infections. The state hasn't had a day without a COVID-19 death since Aug. 15, but the preliminary total of 492 deaths in February is below the peak of 1,073 in December.

Minnesota this week revised its reporting of COVID-19 vaccinations to emphasize the importance of booster doses to address waning immunity. Only 49% of Minnesotans 5 and older are considered up to date, meaning they have received the initial two-dose series if they are 5-11, or booster or additional doses when recommended if they are 12 or older.

Booster rates decline by age groups from 84% among vaccinated seniors to 36% among Minnesotans 12-15, according to state data, which exclude some vaccinations provided at federal facilities.

State officials said lower vaccination rates by age group have played a role in the changing COVID-19 mortality trends. While 82% of Minnesota's 12,264 COVID-19 deaths have been seniors, who are most vulnerable to the disease, that rate has been 71% since July 1.

An estimated 70% of Minnesotans have temporary immunity against the omicron coronavirus variant now based on vaccinations and recent infections, according to the Institute for Health Metrics and Evaluation in Washington state.

Immunity should be widespread enough to suppress COVID-19 through spring and much of the summer in the United States, O'Horo said. "The fall remains the big unknown, and that's where it's going to be important for all of us to keep an eye on ... recommendations on vaccination and if there is a need for some sort of recurrent or seasonal vaccination to prevent something like this from coming back next winter."

Only Rice County is in the high-risk range for coronavirus transmission that carries a recommendation for indoor public mask-wearing, according to a Thursday update from the Centers for Disease Control and Prevention. The rest of Minnesota is in the moderate- or low-risk range based on the burden COVID-19 is placing on local hospitals.

The faster-spreading delta and omicron variants of the coronavirus caused the last two waves, and public health officials continue to watch for signs that a BA.2 omicron subvariant could spark another increase in cases.

The subvariant made up 17% of viral material detected last week in sewage at the Metropolitan Wastewater Treatment Plant in St. Paul. However, the total amount of viral material is declining and is only 2½ times above the lowest levels recorded last June.

Breakthrough infections increased in vaccinated people this winter, mostly because omicron was so widespread, but a researcher with St. Luke's Regional Health Care System in Duluth co-authored a report Friday showing the vaccine remained effective in children.

The CDC study showed the vaccine was more effective against the delta variant, but reduced the risk of omicron infection by 59% in children 12-15. A lower-dose version reduced the risk by 31% in children 5-11.

Weekly surveillance testing of children in four states found that half of omicron infections were asymptomatic compared with one-third of delta infections, the study showed. Symptomatic children who had been vaccinated spent a half day less in bed on average than unvaccinated children.

"The infections observed in this study in the youngest population were largely with omicron, which is recognized as a milder strain of virus," said Dr. Harmony Tyner, the St. Luke's researcher who urged more pediatric vaccinations. "COVID is likely to continue circulating in the population and we may not be so fortunate as to have mild strains in the future."