What will herd immunity look like?

MADISON, Wis. — We’ve all heard experts say the goal is to get to herd immunity. For Public Health Madison and Dane County, that means between 60 and 90% of the population is vaccinated or has coronavirus antibodies.

Currently, 55% of Dane County residents have gotten at least one dose of a vaccine.

Herd immunity doesn’t mean the virus will disappear. It will still be in the community, but we would see fewer infections, hospitalizations and deaths.

“It really is about where the virus or the disease meets a dead end,” said Dr. Matt Anderson at UW Health. “I hear about when my dad was growing up and parents being concerned to send their kids to the pool in the summer because Polio virus was being transmitted and such. I’ve never thought about that once.”

The hope is that our grandchildren will feel that way about COVID. But that will only happen if we reach herd immunity with coronavirus like we did with Polio.

“There’s not any sort of like magic threshold, or any day that we’re going to have a herd immunity day,” said Brittany Grogan, a data analyst at Public Health Madison & Dane County.

In a blog post, Grogan published some of the numbers the department is looking at to understand vaccine access and equity. By looking at the percentage of people who are not eligible in each racial group, you can see where disparities would remain even after we reach herd immunity.

“Our Hispanic and Black populations are younger than other groups, with around 30-32% being under the age of 16. So that means that nearly a third of those populations are not eligible to receive a vaccine,” said Grogan.

Not Eligible Chart

But there are also numbers that give hope. 92% of people 65 and older in Dane County have received at least one dose of a vaccine.

When we think about what herd immunity will look like, Grogan said it will be similar to what we are seeing in the 65+ population right now. It has been weeks since the last case linked to clusters in long term care facilities, and less than 2 new cases per day are being reported.

“Herd immunity doesn’t necessarily mean absolutely zero cases from that point, but enough that we’re not going to see another spike or another wave of these outbreaks,” said Grogan.

She said it is likely we will still have outbreaks similar to the one we had at a Dane County daycare earlier this month. But with more people vaccinated, hopefully less people will be infected from a single outbreak.

With about 20% of people in Dane County under the age of 16 and not eligible for a vaccine, that means to reach herd immunity we will need a large number of those eligible to get a shot.

“If you’re not doing it for yourself, do it for your neighbor. Do it for somebody who can’t be vaccinated. Do it for somebody who is immune suppressed who maybe their body didn’t amount the immune response that we would have liked for them to have had because they’re getting chemotherapy,  because they have some other disease,” said Anderson.

Even though Dane County’s vaccine numbers look good, state and national numbers need to also reach herd immunity for the community to truly get back to normal.

“Dane County is not an island. So even if we have vaccination rates that are at herd immunity levels, people travel in and out of the county all the time. And transmission can still occur among people who aren’t vaccinated,” said Grogan.