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The dramatic drop of COVID-19 cases in Michigan and the significantly lower rates of community transmission are providing a safer environment for Michigan residents regardless of vaccination status.
But we haven’t reached herd immunity yet, and it’s not something that people who lack immunity should bank on for protection, experts say.
“We’re never going to get national herd immunity. That ain’t gonna happen,” said Dr. Liam Sullivan, a Grand Rapids infectious disease specialist with Spectrum Health. “Just like the ship for eradicating coronavirus in the human population sailed a long time ago, the ship for getting herd immunity in the total population in the United States has sailed, too.
“But I think there will be certain pockets of the population where we will have substantial herd immunity,” he said, giving Leelanau County as an example.
“Leelanau has the best immunization rate of any county in the state and if they’re not at local herd immunity, they’re pretty darn close,” he said.
In fact, the county — which forms Michigan’s pinkie finger in the northwest Lower Peninsula and includes a sliver of Traverse City — had no new confirmed cases of COVID-19 in all of June. Almost 73% of Leelanau’s 22,000 residents, which includes children too young to be vaccinated, have had at least one dose of vaccine, according the federal Centers of Disease Control.
But it will be hard for Leelanau to keep out COVID-19, Sullivan said. “The problem from them is that people from outside the county can bring it in, and Leelanau and Traverse City are big tourist areas. So that sort of dilutes the herd-immunity thing up there.”
Indeed, experts say that many people misunderstand the concept of herd immunity and how it works in the real world.
Below is a quick look at what people should know about herd immunity.
How herd immunity works
The concept of herd immunity basically comes down to the power of numbers. When enough people are immune to a virus — through either natural immunity or vaccination — outbreaks are controlled or prevented simply because there aren’t enough people for the virus to infect.
Sullivan compares it to a nuclear reactor. Like a nuclear fission, contagious disease can result in a runaway chain reaction. In the case of nuclear power, “you start sticking rods inside of the reactor to control the reaction,” Sullivan said. “The more rods you put in, the more it slows things down to the point where if you get enough rods in there, it shuts down the reaction.”
With contagious disease and vaccination, “it’s the same concept, only instead of rods you have people who are immunized,” Sullivan said. “If you keep getting more and more people immunized, it stops” the chain of infection.
Vaccination vs. natural immunity
While people can gain immunity by acquiring the disease, Sullivan and others point out that vaccination is a much quicker and safer process.
In the case of COVID-19, the CDC estimates during the first 13 months of the pandemic, 24% of Michigan’s population obtained natural immunity to COVID-19, which includes undiagnosed cases. That estimate is based on the results of 1,345 antibody tests performed statewide by commercial labs between April 5-18.
By comparison, it’s taken less than half the time for Michigan to immunize twice as many people through vaccination, without the downsides of widespread deaths and severe illness that have overwhelmed Michigan’s the health-care system during surges in spring 2020 and 2021 as well as late last fall.
Moreover, no disease has ever been eliminated through natural immunity, Sullivan says, pointing to examples such as measles and smallpox that weren’t largely squashed until mandatory vaccines were implemented for each.
Herd immunity on an individual basis
While public health officials often look at the big picture of herd immunity — evidence President Joe Biden’s drive to vaccinate 70% of the U.S. adult population by July 4 — what matters to individuals is their own community of social contacts.
“It really has to do with your own herd,” said Emily Martin, a University of Michigan epidemiologist. “That’s the people you come in direct contact with, the people around you, as well as the social network for those people.”
In other words: What matters for an individual is the vaccination status of their friends, family and co-workers that they see in person, as well as the people at their church, school, neighborhood and local grocery store.
And because people who are unvaccinated tend to be in social circles with other people who unvaccinated, herd immunity can quickly evaporate for an individual even in a county with high vaccination rates, Martin said.
That’s the pattern seen in measles or whooping cough outbreaks, she said. Even when “vaccination rates look pretty solid” from a state or county perspective, outbreaks can still occur in a school and/or religious community where vaccination is not the norm.
What that means for COVID-19: Even in counties with high vaccination rates, there will be pockets vulnerable to COVID outbreaks going forward.
“So certainly in places where there’s low vaccine uptake at the county level, you would expect more outbreaks,” said Ryan Malosh, another U-M epidemiologist. “But even in a high-vaccinated county like Washtenaw, wherever there is a pocket of low vaccination, you could see small-scale outbreaks.”
Importance of participating
Dr. Jennifer Morse, the public health medical director for 19 counties in the northern Lower Peninsula , is frustrated by the numbers who don’t plan to be immunized and say they’re relying on herd immunity.
She points to a poll by the Kaiser Family Foundation that found 29% of adults in rural communities said they will not get the vaccines.
“There’s a lot of, ‘Not my kid or not me. Everybody else can do it and then I’ll be protected,’ ” she said. “But unfortunately, if you have 29% of people saying ‘I’m not going to do it; let someone else do their herd immunity for me,’ that’s going to be a problem.”
That’s absolutely true, Sullivan said.
“The key thing about herd immunity is that people can’t just say, ‘Well, I’m going to rely on herd immunity,’ ” and avoid getting vaccinated, he said. “You’re part of the herd. We’re all part of the herd. If we truly want herd immunity to work, we all have to participate in it.”
Why herd immunity is important
People who decline to get vaccinated often take the stance that if they don’t want to be immunized, they aren’t hurting anyone except themselves.
But that’s not the case, health experts say.
Herd immunity is important because it creates a protective bubble around children too too young to be vaccinated; people with medical conditions that prevent vaccination; those undergoing cancer treatments or whose immune systems have been weakened; elderly persons whose fading immune systems make them more vulnerable to breakthrough infections, even if they are fully vaccinated.
And with COVID-19, the number of vulnerable people is exceptionally large because vaccinations aren’t yet available for children under 12. In Michigan, that’s 1.4 million residents right there.
Herd immunity also is important because as long as COVID-19 continues circulating, it continues to mutate. And while the current vaccines have held strong against the variants that have surfaced so far, that may not always be the case.
“It’s a basic, common-sense threat and it has implications for global vaccinations,” said Marcus Cheatham, who head the Mid-Michigan District Health Department, which covers Clinton, Montcalm and Gratiot counties. “As long as the virus is alive and mutating, it will find ways to break through the vaccines, as good as they are.
“So for our own safety and well-being, we need to stop it,” he said about transmission of COVID-19. “We can look inside Michigan and say we need to stop it from mutating in Michigan, but we really need to do that globally. This is not an esoteric point at all. It’s just basic Virus 101.”