Population health experts are divided on whether Michigan and the rest of the country can truly achieve herd immunity against COVID-19 based on current trends.
Herd immunity occurs when enough people are immune to a disease to keep it from spreading in the community. That typically happens when about 70% to 80% of the population has developed antibodies against a disease or virus through either infection or vaccination, said Michigan State University epidemiology professor Nigel Paneth.
It’s possible that Michigan could reach 70% immunity as early as October, Paneth argued, provided vaccinations continue to be administered at their current pace and a few other things happen.
But Ali H. Mokdad, a professor of Health Metrics Sciences at the Institute for Health Metrics and Evaluation at the University of Washington, said about a quarter of people who say they will refuse the vaccine — which puts the achievement of herd immunity in doubt across the country, including Michigan.
Based on data collected as part of the Facebook Global Symptom Survey, an ongoing survey of Facebook users to monitor the spread of COVID-19, about 73% of Michigan residents answered Yes, or Maybe Yes, when asked if they would take the vaccine, he said.
“So more than 25% of people in Michigan are not willing to take the vaccine,” Mokdad said. “Herd immunity’s not gonna happen this year for sure.”
And Dr. David Rubin, director of the PolicyLab at Children’s Hospital of Philadelphia, said herd immunity shouldn’t be the goal. His team has constructed county-level models to project future cases in more than 800 U.S. counties — including more than 15 counties in Michigan — based on current social distancing practices.
“I don’t think herd immunity is what we’re looking to achieve here because I don’t think it’s realistic,” Rubin said. “What we do need to get to is COVID being an endemic virus” — that is, regularly occurring.
“I don’t think we’re ever going to eliminate COVID. What vaccination is doing is reducing the risk of severe disease, not necessarily reducing the risk of transmission.”
Where Michigan stands
The Michigan Department of Health and Human Services has set a goal of vaccinating 70% of adults age 16 and older in the state, or about 5.6 million people, as soon as possible, said Michigan Department of Health and Human Services spokeswoman Lynn Sutfin.
Part of the reason for the state’s goal is there is no vaccine that has been approved for emergency use in children younger than 16.
Only the Pfizer vaccine is approved for use in 16- and 17-year-olds, while the Moderna and Johnson & Vaccine shots can only be used on adults 18 years and older. Pfizer reported Wednesday that preliminary data from its own study of 2,260 U.S. volunteers ages 12-15 found no cases of COVID-19 among fully vaccinated adolescents compared with 18 among those given dummy shots.
The ability of states to meet their vaccination goals depends in part on how many vaccines they get from the federal government. Health providers complained earlier this year that they weren’t getting enough doses. But the Biden administration has increased the weekly vaccine allotments in Michigan and other states in recent weeks.
Michigan’s vaccine allocation from the Biden administration is going to hit a record high of 620,040 doses next week — up from the 554,020 doses of Pfizer, Moderna and Johnson & Johnson vaccine received the week of March 28. and 465,500 doses expected for the week of April 4, according to the state health department.
This was up from 343,875, the highest number of vaccine doses shipped to Michigan during any one week in January.
Gov. Gretchen Whitmer said Wednesday that she is raising the state’s vaccination goal from 50,000 shots administered per day to 100,000 shots.
Through Monday, about 20.1% of Michigan’s adult population of 8.1 million had been fully vaccinated, according to Michigan’s COVID-19 Vaccination Dashboard. About 33.8% of adults had received at least their first dose of vaccine.
The proportion of the population that is immune to COVID-19 is derived by adding the fraction that has been vaccinated to the fraction that was infected with the disease — about 20% across the country is Paneth’s estimate.
By that back-of-the-envelope estimation, roughly 40% of Michigan’s adult population is immune.
Meanwhile, COVID-19 cases among Michigan’s kids ages 10-19 have risen faster than any other age group in the past month as the state confronts another spike in virus cases, according to the state health department.
It’s also the first time during the pandemic that this age group has led in confirmed and probable cases in Michigan, according to data from the Michigan Department of Health and Human Services. But the level is well below the surge of cases experienced in November and December.
The federal Food and Drug Administration has not yet authorized any vaccine for children, and independent clinical trials for children younger than 16 have just begun, Paneth said. They aren’t expected to be approved for emergency use until next year at the earliest.
“We’re going to have to vaccinate the children too because they still could be a reservoir,” Paneth said. “We can’t leave them out. We might be getting close (to herd immunity). But we still need to vaccinate the kids.”
The inability to vaccinate children is among the reasons why the University of Washington’s Mokdad doesn’t think it’s possible to achieve herd immunity anywhere in the country this year.
“We are far from reaching herd immunity in Michigan, and in the United States and all states in the U.S.,” Mokdad said. “Simply because right now the vaccines are only authorized for adults.”
Some states ahead on immunity
Some states that imposed fewer restrictions and exposed more people to the virus appear to be closer to achieving herd immunity than states like Michigan, according to one expert. They include Florida and Oklahoma, said Dr. Aaron Wendelboe, an associate professor of epidemiology at the University of Oklahoma Health Sciences Center.
Florida Gov. Ron DeSantis never imposed a mask mandate, and in September banned local communities from having their own mask requirements. Tourist crowds have inundated Miami Beach. The number of cases has begun to rise in a state with the largest number of cases of the United Kingdom variant that is more contagious and potentially more deadly.
Oklahoma was consistently among the top five states in cases per capita because it “didn’t do as great a job preventing infections as we could have,” said Wendelboe, whose statistical model estimates 68% of the state’s population had some sort of exposure to COVID-19.
“So I think we can get to that 70% threshold sooner than other states,” he said. “Other large states like New York and Michigan that took COVID seriously, you did a good job preventing further disease, so you have a larger susceptible population.”
Oklahoma’s number of confirmed new cases is shrinking, with 2,403 for the seven days ending March 29 compared with 2,657 for the seven days prior. This is happening even though Gov. Kevin Stitt announced on March 11 he would roll back his few remaining COVID-19 restrictions, including limits on public gatherings and a mandate that masks be worn in state buildings.
Oklahoma and Florida are statistically similar, said Wendelboe, who focuses on infectious disease transmission dynamics, outbreaks and surveillance as well as microbiology.
“Early on in the epidemic, Florida led the country in cases for a very long time,” he said. “They built up some herd immunity because people in Florida were more cavalier, maybe not wearing masks as much.”
“Their situation is just like Oklahoma, where they experienced cases upfront,” he said. “That’s a huge part of the equation.”
Variants threaten immunity
MSU’s Paneth said his biggest concern is that while waiting for herd immunity, the virus could spin off a deadly new variant.
“The worst thing that could happen, you get a mutation that doesn’t care about the vaccine,” he said.
According to Paneth, viruses don’t generally mutate when they’re inside a person’s body. Mutation is most likely to happen during transmission from one person to another — and that’s why huge gatherings like the recent street parties in Miami Beach are breeding grounds for variants.
“You’ll see signals of that when people start getting COVID again because their antibodies aren’t good enough to sustain them against any new variants,” Paneth said.
Rubin of Children’s Hospital of Philadelphia said the spike in Michigan’s case numbers is likely related to a rapid increase in gatherings and mobility throughout the state.
“I’ve been looking at social distancing information for mid-Michigan because your resurgence is an outlier in the country right now,” Rubin said. “You can see a very dramatic shift in people’s mobility throughout the state of Michigan.
“The amount of travel to non-essential business like restaurants — you’re back to pre-pandemic rates. … Gatherings and mobility have increased rapidly and vaccinations have not yet caught up.”
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