More breakthrough COVID infections means more people could be mildly infected and not know it

Over the past several weeks, at least two dozen of Dr. Laura Zimmermann’s patients, all fully vaccinated against COVID-19, tested positive for the virus.

All had mild cases, reinforcing that vaccines are largely preventing death and hospitalization from the virus.

But the recent rise in infections among the fully vaccinated makes her wonder how many people are walking around with what’s now the dominant form of the virus — the highly contagious Delta variant — and spreading it.

“I’ve seen more breakthrough infections from the Delta variant,” said Zimmermann, a preventative care specialist at Rush University Medical Center. “Early on, I saw a handful of cases — among people working in the healthcare environment. Now, even young patients who are fully vaccinated are getting infected.”

Some health experts estimate one in five COVID cases is among fully vaccinated individuals.

But Illinois and the federal government aren’t tracking the data unless cases result in hospitalization or death.

What Zimmermann and other doctors keep asking is how many vaccinated people carrying the virus pass COVID on to those who are not protected at all?

That’s a worry exacerbated by Delta. Until a vast majority of people are vaccinated, the virus is likely to get more difficult to control. The worst-case scenario is that it mutates into a form that current vaccines won’t fight.

In Chicago, health officials estimate about 800,000 people have no protection from the virus. They haven’t been vaccinated or gotten infected.

Almost all serious COVID cases are among the unvaccinated. But data on breakthrough infections can help set public health guidelines, especially now that students are back in full classrooms, entertainment and sporting venues are back at capacity limits, extended families are reuniting and workers are returning to offices.

“We should be doing everything we possibly can to stop this thing,” said Beth Blauer, a Johns Hopkins University associate vice provost who leads COVID data analysis. The data “could be life saving, it could transform public health.”

Tracking breakthrough COVID is spotty because the federal Centers for Disease Control and Prevention stopped asking that the data be tracked in May — before Delta cases surged. Breakthrough infections resulting in deaths or hospitalizations — fewer than 1% of cases in Illinois — are the focus.

The numbers are rising. There were more than 2,000 hospitalizations and almost 600 deaths among fully vaccinated people in Illinois through the end of September, quadruple the numbers at the beginning of July. Most of the deaths and hospitalizations are among those 65 or older.

Citing the CDC recommendations, Illinois health officials don’t provide data on mild breakthrough cases.

Cook County health officials say about 8% of cases since January are fully vaccinated people, though that number is likely understated and may be as high as 20%, said Dr. Rachel Rubin, the county’s senior public health medical officer.

More than 10% of infections tracked by the Chicago Department of Public Health are believed to be among fully vaccinated people, though a spokesman said that, too, is probably an undercount.

Without being tested, vaccinated people likely don’t know they’re carrying the virus because symptoms can be mild or nonexistent.

“We are not protecting the people who are not vaccinated,” said Dr. Monica Peek, a University of Chicago internist.

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Vaccinated people might be lulled into a false sense of security and let their guard down, like failing to mask or social distance around others indoors, which increases the spread of the virus, said Dr. Maya Green, regional clinical director for Howard Brown Health.

“It’s going to mutate and try to circumnavigate the vaccine,” Green said. “I am vaccinated, and I can still get the virus. That’s how vaccines have always worked. Historically, there’s no vaccine that is 100% effective.”

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Also, the Delta surge ramped up just as kids headed back to school, a concern as children under 12 are not eligible to get vaccinated, said Dr. Jennifer Pisano, a University of Chicago infectious diseases specialist.

“The point about transmission is still concerning, especially since kids are not vaccinated,” Pisano said.

Even gatherings of family outside households carry risk, said Susan Bleasdale, assistant vice chancellor for quality and patient safety at University of Illinois at Chicago.

“You have to make a choice about when you take your mask down and who you’re with,” said Bleasdale.

Zimmermann said don’t dismiss what appears to be signs of a cold or allergies because these could be mild COVID.

“We in the U.S. are traditionally workaholics and martyrs who come to work sick,” Zimmermann said. “That is the norm. That norm has to change. If you are sick, stay home. Stay home, get tested, contact your doctor.”

Brett Chase’s reporting on the environment and public health is made possible by a grant from The Chicago Community Trust.