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Post-vaccine COVID-19 cases are uncommon, but St. Louis County experts urge caution

Post-vaccine COVID-19 cases are uncommon, but St. Louis County experts urge caution


ST. LOUIS — The St. Louis County health department has identified 71 people who tested positive for COVID-19 after they were fully vaccinated, the first public acknowledgement that some who got the vaccine have, as expected, gotten the virus, too.

Experts say the findings reinforce that, even post-vaccine, people still need to be cautious.

“That’s important to tell people, because if you’re vaccinated, you kind of feel like you’re bulletproof,” said Dr. James Hinrichs, infectious disease advisor for the St. Louis County Department of Public Health.

But such incidences are extraordinarily rare: As of Monday, 339,000 people in St. Louis County have received at least one dose of vaccine, and 226,000 have been fully vaccinated, according to state data — meaning just 0.03% of those fully vaccinated are known to later have gotten COVID-19.

Nationally, the U.S. Centers for Disease Control and Prevention reported last week that it had received 5,814 reports of breakthrough infections, or about 0.008% of the more than 75 million people fully vaccinated.

The CDC defines a breakthrough case as someone infected with COVID-19 more than two weeks after the second in a two-dose series, such as that from Moderna or Pfizer, or two weeks after a one-dose vaccine, such as that from Johnson & Johnson.

Dr. Rachel Presti, medical director of the infectious diseases clinical research unit at Washington University, said that the number of breakthrough infections in the U.S. is in line with what experts expected.

“These vaccines might be 95% effective, so they were never going to prevent all cases,” Presti said. “The numbers of infections so far seem in line with the efficacy of the vaccines.”

Dr. Sarah George, an associate professor of infectious diseases at St. Louis University Medical School, said the national rate of breakthrough cases is “actually pretty darn good. We see higher rates than that in cases like influenza vaccinations.”

In St. Louis County, Hinrichs said breakthrough cases are identified when the health department contacts people who have tested positive for COVID-19. Those people are asked whether they have been vaccinated, and if so, when they received each dose.

At least 40% of the breakthrough cases were asymptomatic, Hinrichs said. Those individuals usually were tested because they had a household member with COVID-19. And 44% of the infections were among health care workers, which he suspects is largely because they were vaccinated first, and therefore have been fully vaccinated for a longer time.

Hinrichs said if a vaccinated person has a household member who becomes ill, they should consider wearing a mask and staying distanced until that person is tested.

Among the first 50 breakthrough cases St. Louis County examined, Hinrichs said the ages ranged from 27 to 77, and the average was 52.

“Even though this is a rare event, it does make you pause to kind of rethink what your behaviors should be,” Hinrichs said.

Of those who had symptoms, the vast majority were very mild. Two people were hospitalized. One was discharged on Thursday, Hinrichs said, and the other still was in a hospital as of Saturday.

“People might have the obvious question: Are these variants that are causing this?” Hinrichs said. “And I wish I had an answer to that.”

With breakthrough cases, the department tries to track down the sample taken during the COVID-19 test, and send it to the state so it can be tested for the presence of COVID-19 variants. Hinrichs said Monday that he had sent five samples to the state so far, but did not have the results yet.

Presti and other Washington University researchers are now conducting a study on breakthrough infections among their patients. The researchers are collecting samples from participants who got COVID-19 after vaccination and will be attempting to analyze how the patients’ immune systems worked against the virus.

“We’ll be looking at the specific antibody response to see why it didn’t prevent infection,” Presti said.

So far, Presti said both national statistics and her observations of the patients in the study show that cases of COVID-19 after vaccination also tend to be less severe. She emphasized that eligible adults should get vaccinated.

“You have to focus on the actual risk. If you wear a seatbelt and get in a car crash, you could still get injured and die,” she said. “But if you don’t, the chances of that are much higher.”

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