New data from the Wisconsin Department of Health shows people who have been vaccinated and boosted against COVID-19 became infected at higher rates than those who were not vaccinated in April. However, the state’s epidemiologist emphasizes that the data is clear that the effectiveness of vaccines in preventing serious illness and death remains high.
DHS updated its Post-Vaccination Illness webpage Thursday to include data on individuals who received booster shots after completing their vaccination course. It shows that in April, the rate of confirmed and probable COVID-19 cases was highest among those who completed the series and received a boost, at 507 per 100,000. Those who were unvaccinated had an infection rate of 420.8 per 100,000. Those who had completed the vaccination course but not received a booster had an infection rate of 211.5 per 100,000.
During a media briefing, state epidemiologist Dr. Ryan Westergaard states that the data is from hospital and local health agency reporting and is not a randomized clinical research study and that there are potential biases built into the data.
“People who get a booster shot may also be more likely to be tested if they develop symptoms,” Westergaard said. “People who get a booster shot may change their behavior so they are more exposed. There are a number of explanations.”
Westergaard said the bottom line is that the effectiveness of current vaccines at preventing infection by Omicron variants of the coronavirus has decreased.
“But effectiveness in preventing death and serious illness has remained high‘ Westergaard said.
April DHS data shows unvaccinated Wisconsin residents were twice as likely to be hospitalized as vaccinated residents. Unvaccinated residents were seven times more likely to die from COVID-19 than those who completed their vaccination course.
Coronavirus infections rose in May, although the latest data shows a slight drop in cases. On Thursday, DHS reported a seven-day average of 1,823 new cases. That’s down from a seven-day average of 2,201 cases reported on May 15.
“So we’re optimistic that the weather stays nice, if people get vaccinated and recover and have some immune protection, that this wave won’t be as strong as what we’ve seen in the past,” Westergaard said.
But Westergaard said despite the slight decline and new antiviral drugs becoming available in hospitals to treat serious COVID-19 illness, people need to be cautious over Memorial Day weekend.
“One lesson we’ve learned repeatedly in the more than two years of the pandemic is that there is a risk of transmission on holiday weekends like Memorial Day, when people gather,” he said.