New University of Minnesota research is assessing whether COVID-19 vaccines protect people with compromised immune systems — a key group excluded from vaccine clinical trials.

While evidence shows COVID-19 vaccine effectiveness in the general population, there is little known about how the shots work in people with HIV or taking immune-suppressing drugs as part of their cancer care or organ transplants, said Dr. Amy Karger, a lead investigator of the university study.

“We really need to dig deeper and look at these groups, where we know they have something that could be impairing their ability to mount an immune response,” she said.

Minnesota has counted 604,291 infections with the coronavirus that causes COVID-19, and 7,531 deaths — including 115 infections and four deaths reported Friday. The state also reported 132 COVID-19 hospitalizations, down from 699 on April 14 at the peak of this spring’s wave.

Vaccination progress in Minnesota has been credited with shortening the duration and severity of the spring wave — with more than 3 million people 12 and older in the state receiving at least a first shot and nearly 2.8 million people completing the one- or two-dose series.

While other researchers study whether people need booster doses over time to maintain protection, Karger said the U study will establish whether the initial doses work in the immunocompromised population. The study is part of a $6.7 million grant the U received as part of the national SeroNet research group.

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Unvaccinated people with weakened immune systems had been protected by mask-wearing and social distancing that reduced viral transmission in their communities, but those practices have declined over the past month since state mandates were lifted.

The U is recruiting 2,000 people who have either recently received vaccine or are about to receive their first dose — a challenge now that 64% of all eligible people 12 and older have received their shots — and will monitor the antibody levels in their blood over two years.

“Minnesota has been so successful with vaccination … that our pool is ever-shrinking,” Karger said.

The U planned last fall to study the duration of natural immunity in people after coronavirus infections. While public health guidance suggests protection lasts 90 days in most people, Karger said there is credible evidence that protection lasts eight months or more in people with healthy immune systems.

“Ninety days seems to be old news,” said Karger, although the duration of protection in immunocompromised people remains less clear.

Federal approval of COVID-19 vaccines in December shifted the U research toward duration of immunity after people received their shots.

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“I do think the booster shots and future shots and timing and doses are going to be really important questions that we need to tackle,” she said.

Researchers at Johns Hopkins University in Baltimore this week reported improved protection in some organ transplant recipients who received a third booster dose of COVID-19 vaccine.

Separate research in Minnesota also has contributed to the ongoing review of the safety of COVID-19 vaccines.

Doctors with the Minneapolis Heart Institute Foundation this week published details of four vaccine recipients 16 to 31 who suffered myocarditis, an inflammation of the heart muscle that was found in enough recipients to prompt a review next week by the federal Advisory Committee on Immunization Practices.

Two of the patients with the inflammation had received first doses of vaccine after suffering coronavirus infections. The other two had received two doses but hadn’t suffered prior infections. “This research isn’t a definitive answer, but it adds to the clinical insights available and encourages ongoing study and diligent monitoring,” said Dr. Mario Göessl, a cardiologist and researcher with the Minneapolis foundation.

Researchers this week at nference, in partnership with Mayo Clinic in Rochester, also published a review showing that COVID-19 vaccination was not significantly linked to the development of cerebral venous sinus thrombosis, a blood clot.

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Equal numbers of clots were found before and after vaccination in a group of Mayo patients, suggesting they weren’t influenced by vaccination, said Venky Soundararajan, co-founder and chief scientific officer of nference. “This study comes at a critical moment in the pandemic and provides independent evidence that it is generally safe to be vaccinated against COVID-19.”

Most people in the study received either Moderna or Pfizer doses, which haven’t been linked to blood clot risks.

Usage of the Johnson & Johnson vaccine was paused briefly in the U.S. this spring to assess clots found in some recipients, but then resumed without restrictions when federal health officials concluded the benefits outweighed the small risks. The low number of recipients of that vaccine in the nference study limited its findings.