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MI's herd immunity challenges: What we can learn from 2019's measles outbreak

Posted at 6:21 PM, May 12, 2021
and last updated 2021-05-12 18:32:54-04

Talk to experts and they all say the same thing: Vaccination — or infection — is the only way out of this pandemic. The end goal? Herd Immunity.

"It’s what we need right now to really end this pandemic," said Dr. Aimee Gordon, an associate professor of epidemiology at the University of Michigan. "There’s two ways to get to herd immunity. Either thru vaccination, which certainly preferable, or infection."

But getting there has become more difficult. New, more contagious strains of the virus mean the bar is higher. Experts once believed we needed 70% of the population to be infected or vaccinated, but now that figure is going up.

"To get to herd immunity the estimates are somewhere between 80 and 90% of people have to be vaccinated," said Dr. Matthew Sims, Director of Infectious Disease Research for Beaumont Health. "And that will include children."

This children factor is one that the state has not yet built into its metrics around vaccine completion. On Tuesday, for example, the state’s COVID database said 43% of the population has been fully vaccinated, but the stat comes with a caveat: It’s based on US Census estimates for the state population of people 16 and older.

"That makes a big difference," said Dr. Sims.

When you take into account the entire population-- including children—that percentage of fully vaccinated people drops to 36%.

And that’s why experts say kids will play a large role in this effort.

"In the US, children under 18 are 25% of the population," said Dr. Aimee Gordon.

This week the FDA granted Pfizer emergency authorization for children ages 12 to 15 to get the 2-dose shot. That should help in the herd immunity effort -- But it also comes with new era-specific challenges.

"Why did we have breakthroughs back when we had all the measles outbreak? It’s because vaccination of children has gone down significantly," said Dr. Sims.

In spring 2019 Michigan became a hot spot in a nationwide measles outbreak. More than 40 people were infected.

"A lot parents opted not to vaccinate their children and that became a big problem," said Dr. Sims, who sees the issue as something of a catch-22: because vaccines have been so effective during the last few decades, younger people don’t necessarily realize how bad it could be without them.

"They say, ‘Well there are so few cases around why should we give this vaccine?’" said Dr. Sims. "Well, it’s a little bit a chicken and egg, right? There so few cases around because of vaccination."

The recent measles outbreak highlights what happens when people opt out — and provides a blueprint for COVID.

"It just goes to show you," said Dr. Sims, "that if you don’t have enough people getting vaccinated if you have susceptible hosts, susceptible people, the disease is going to spread."

While Michigan will track the vaccination rates in kids and teens, the state says it won’t count them towards benchmarks for easing pandemic restrictions.