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Study: Some vaccinated and unvaccinated people in Wisconsin have similar COVID-19 viral loads

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Posted at 9:35 PM, Aug 04, 2021
and last updated 2021-08-05 12:03:05-04

MADISON — Some vaccinated Wisconsin residents infected with COVID-19 in June and July had as much virus in their nasal passages as newly infected, unvaccinated people, according to a new study.

Researchers at UW–Madison, Public Health Madison & Dane County and Exact Sciences say their findings match those from the CDC study that describes a COVID-19 outbreak in Massachusetts.

The Wisconsin researchers say their study suggests the bottom line is that fully vaccinated people who get sick with coronavirus could infect others.

The researchers studied nearly 300 COVID-positive samples collected in Wisconsin between June 28 and July 24. Their analysis showed no significant difference in “viral load” between 79 fully vaccinated people and 212 unvaccinated people.

Both the vaccinated and unvaccinated people had high viral loads during their positive tests, enough to make them contagious to others, according to the study.

Katarina Grande, co-author of the study and public health supervisor and COVID-19 Data Team lead at PHMDC, 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."

42 of the cases studied were identified as the delta variant. 50 out of the original 300 samples underwent genetic testing to determine which strain of the virus was present.

The findings don't diminish the importance of the vaccine, researchers say; the vaccines remain effective in keeping people from getting severely sick - even against the delta variant.

“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 and co-author of the study. “As long as the vaccines are keeping people out of the hospitals, I would say they’re working spectacularly well.”

Read the UW's summary of the study by clicking here.

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