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Virus levels high in Wisconsin COVID-19 cases, even among fully vaccinated
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COVID-19 | WISCONSIN STUDY

Virus levels high in Wisconsin COVID-19 cases, even among fully vaccinated

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Hanson preparing syringe (copy) (copy)

Mark Hanson, a registered nurse, is one of many retired volunteers who help the Middleton-based Benevolent Specialists Project Free Clinic provide COVID-19 vaccinations and a wide range of specialty medical care.

Some vaccinated people infected with COVID-19 in Wisconsin in June and July had as much virus as newly infected unvaccinated people, meaning they can also readily spread infection, according to a new study by researchers in Madison.

The findings echo a recent Centers for Disease Control and Prevention report describing an outbreak centered in Cape Cod, Massachusetts. The CDC study focused on cases arising from a handful of large public gatherings, while the new Wisconsin results came from more everyday circumstances.

Analysis of nearly 300 COVID-positive samples collected in Wisconsin between June 28 and July 24 showed no significant difference in “viral load” between 79 fully vaccinated people and 212 unvaccinated people, according to a study by researchers at UW-Madison, Public Health Madison and Dane County and Exact Sciences.

The vaccinated and unvaccinated study subjects had high viral loads at the time of their positive tests, levels shown in previous studies to be substantial enough to make them contagious to others, the researchers said.

“This is what the CDC’s study showed last week in a single outbreak, but we are seeing the same in a more distributed sample across our state,” Katarina Grande, co-author of the new study and leader of the COVID-19 data team at the city-county health department, said in a statement.

The new results show that vaccinated people, who don’t have much to fear in terms of severe disease, must be mindful that they can still be a source of infection for others, the researchers said.

“If there are people in their lives who are vulnerable, they still need to take care to keep those people safe,” said Thomas Friedrich, a scientist at UW–Madison’s AIDS Vaccine Research Laboratory, which has been collecting genetic samples from positive COVID tests. “We still need a community response to the pandemic that includes vaccinated people taking steps to prevent the unlikely — but not impossible — chance that they would transmit infection to others.”

The findings have led the CDC and Public Health Madison and Dane County to return to recommending face coverings indoors for vaccinated and unvaccinated people.

The Wisconsin researchers reported the results Saturday on the preprint server medRxiv, before the peer review process carried out by most journals, as has become more common during the COVID-19 pandemic. UW-Madison released a summary of the findings Wednesday.

Nearly one-third of the study’s cases came from Dane County, where unvaccinated people are being diagnosed with COVID-19 at a rate two-and-a-half times greater than vaccinated people. Some breakthrough infections are expected in vaccinated people because no vaccine is 100% effective.

Of the 50 samples that underwent genetic testing to determine which strain of the coronavirus that causes COVID-19 was present, 42, or 84%, were the delta variant, which appears to be more transmissible. Nearly all new COVID-19 cases in Wisconsin involve the delta variant, including among vaccinated people.

Vaccination remains critical, the researchers said, because the available vaccines against the virus are effective — even against the delta variant — and help prevent new, dangerous cases.

“They’re still working to keep people from becoming infected, though not necessarily as well as they were against earlier types of the virus,” said David O’Connor, a UW School of Medicine and Public Health professor. “As long as the vaccines are keeping people out of the hospitals, I would say they’re working spectacularly well.”

Wisconsin reported 1,180 new COVID-19 cases Wednesday, for a daily average of of 902, the highest since February, when vaccines were scarce.

Some 353 patients were hospitalized with COVID-19 as of Wednesday, including 114 in intensive care. That is well below the peak of 2,277 patients in hospitals with the infection in mid-November but nearly five times the recent low of 74 patients hospitalized with the coronavirus on July 6.

Statewide, 52.3% of residents have had at least one dose of vaccine. Among adults, it’s 63.1%, according to the state Department of Health Services. Higher rates are needed for the “herd immunity” that can prevent outbreaks, health officials have said.

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