Minnesota's COVID-19 breakthrough cases point to vaccine effectiveness

Breakthrough infections might be more common in the omicron era, but fully vaccinated Minnesotans make up less of the state's COVID-19 hospitalizations and deaths.

New state breakthrough data on Monday showed that fully vaccinated Minnesotans made up 55% of 20,502 infections reported in the week ending Dec. 25, but only 26% of the 116 COVID-19 deaths. The share of deaths involving vaccinated Minnesotans was as high as 50% in mid-October, before booster doses were broadly available.

The data suggest a payoff to booster shot campaigns in Minnesota, which ranks second among states with nearly 53% of fully vaccinated residents receiving recommended extra doses, according to the Centers for Disease Control and Prevention.

Overall, nearly 3.8 million Minnesotans have been fully vaccinated with the initial series, or 67% of the state's population. The vaccination level magnifies the disparity in risk for unvaccinated Minnesotans, who make up 33% of the state's population but 64% of COVID-19 deaths and 72% of hospitalizations since May 2.

State health officials are hopeful vaccination progress has blunted the omicron wave, which has caused record infection numbers but appears to be peaking. Mayo Clinic's predictive 14-day model has pushed the state's peak infection date from Jan. 26 to Feb. 3.

"I still think it's a little too early to tell," said Kathy Como-Sabetti, a COVID-19 epidemiology supervisor for the Minnesota Department of Health. "I'm increasingly hopeful but I wouldn't say I'm entirely convinced."

Sewage sampling at the Metro Wastewater Treatment Plant in Bloomington already has shown a decline in viral prevalence in the Twin Cities. However, declines haven't been found statewide. The University of Minnesota coordinates with 44 plants to test wastewater for molecules that indicate the presence of certain strains of the coronavirus.

"We have seen this decrease pretty uniformly across the greater metropolitan area and it's starting to decrease down the 35 corridor in south-central Minnesota — Albert Lea and that area," said Dr. Tim Schacker, vice dean for research at the University of Minnesota Medical School. "But everywhere else in the state, it's still pretty much accelerating. It's still going up, so they have not peaked yet."

Schacker said wastewater sampling can offer two-week predictions of increases in viral activity and will be used more in the future in Minnesota to track the pandemic and others pathogens such as influenza.

Minnesota on Monday reported another 12,722 coronavirus infections and 42 COVID-19 deaths, including four people in their 40s. The state's pandemic death toll is 11,193.

COVID-19 hospitalizations in Minnesota had fluctuated from 1,314 on Jan. 1 to a high of 1,629 on Jan. 19 and back down to 1,566 on Friday. The share of hospitalizations requiring intensive care has declined from 25% last month to 15%, partly because the omicron variant spreads faster but produces a lower rate of severe illness.

The delta variant wave last winter started strongly in rural Minnesota counties with lower vaccination rates before increasing in metro areas. The omicron wave spread in reverse, starting in the highly vaccinated metro areas before spreading outward to the rest of Minnesota.

Bloomington-based HealthPartners joined with health systems from nine other states on Friday to report that booster doses of COVID-19 vaccine were highly effective, even during the omicron wave, in preventing emergency department or urgent care clinic visits and hospitalizations. The researchers verified waning immunity six or more months after patients received their initial vaccine doses.

The Minnesota Department of Health also contributed to a national CDC report on Friday showing the rate of U.S. coronavirus infections last fall was three times lower in fully vaccinated people and 14 times lower in people who had received boosters compared with those who were unvaccinated.

The gap narrowed in December as the omicron variant produced higher rates of infection in all three groups, but the report showed vaccination remained protective.