Dane County approaching herd immunity milestone

Photo by Lauren Bishop, CDC/https://phil.cdc.gov/Details.aspx?pid=24150

By May 14, Dane County projects it will have provided COVID-19 vaccines to 80 percent of those 16 and older, according to the head of the county’s data team.

That’s if the county’s strong vaccination pace continues, Katarina Grande said in a Greater Madison Chamber of Commerce briefing yesterday.

“We still know that we’re not going to see like a ‘herd immunity day’ or a specific moment of declaration,” Grande said. “We also know that the impacts of more transmissible variants like B.1.1.7 have likely impacted and raised that theoretical level needed for herd immunity.”

Herd immunity is when enough people have protection against infection that a community becomes resistant either by vaccination or previous infection. The World Health Organization says there’s not enough information about how long immunity lasts from previous infection, so it supports herd immunity through vaccination. 

“It is difficult to predict how many (people) need to be vaccinated to achieve herd immunity in a population,” said Ajay Sethi, population health sciences professor at the UW-Madison School of Medicine and Public Health. 

The estimated range is between 60 and 90 percent of people fully vaccinated. But currently, 20 percent of the population is ineligible because they are under 16 years old. 

“We are headed in the right direction as more people choose to be vaccinated,” he said in the latest episode of “Badger Talks,” an interview series produced by UW-Madison University Communications. “Ultimately, we want a high vaccination rate among people at any and every type of gathering or group activity that people do normally.”

The U.S. is approaching half of the population getting at least the first dose. Grande said some countries have seen a tipping point after 50 percent coverage. Israel is seeing less than one case per 100,000 people at 60 percent coverage. Dane County is seeing 9 cases per 100,000 people with 60 percent of its population having received at least one dose. Dane County leads the state with that metric.

“There’s still variability here, and there’s no guarantee that just at this coverage level this is what we’ll see,” Grande said. “We acknowledge that uncertainty but also know that the pathway remains that the summer is looking good.”

Dane County is 46.5 percent fully vaccinated as of yesterday, meaning that portion of residents has received two doses of the Pfizer or Moderna shot or one dose of the Johnson & Johnson shot. More than half of every age group has at least started a vaccine series.

Breakthrough infections — when a variant gets passed the vaccination — is “extremely rare,” at .03 percent in Wisconsin, Grande said. 

-By Stephanie Hoff