'Vaccines are working exactly as advertised': What experts say CDC's latest report on breakthrough cases means

·5-min read
'Vaccines are working exactly as advertised': What experts say CDC's latest report on breakthrough cases means

The Centers for Disease Control and Prevention released a new report on Tuesday, detailing just how many breakthrough infections have happened in the U.S. in people who are fully vaccinated against COVID-19. 

The report found that 10,262 COVID-19 breakthrough infections were reported to the CDC from 46 states and territories between Jan. 1 through April 30, 2021. By the end of April, about 101 million people in the U.S. were fully vaccinated against COVID-19.

COVID-19 transmission was at high levels in many parts of the country during the report’s time frame, with about 355,000 new cases nationally during the week of April 24 through April 30.

A member of the Maryland National Guard administers a coronavirus vaccine
A member of the Maryland National Guard administers a coronavirus vaccine. (Chip Somodevilla/Getty Images)

There were some trends in people who experienced breakthrough infections, according to the report:

  • 6,446 (63 percent) were female

  • The median age was 58 years old

  • 2,725 (27 percent) of cases were asymptomatic

  • 995 (10 percent) of patients were hospitalized

  • 160 (2 percent) of patients died

Of the patients who were hospitalized, 289 (29 percent) did not have symptoms or were hospitalized for reasons other than COVID-19. The median age of patients who died was 82, and 28 (18 percent) of those who died did not have symptoms or died from a cause that wasn’t related to COVID-19. 

The CDC has genomic sequencing data from 555 (5 percent) of the breakthrough cases and found that the majority of those were due to B.1.1.7, the variant first detected in the U.K. (56 percent), followed by B.1.429, the variant first detected in California (25 percent). 

The CDC noted that breakthrough infections are likely undercounted, given that people may not see their doctor or get tested for mild infections, and that many asymptomatic infections wouldn't be detected unless people undergo regular screening. 

Overall, though, the CDC says that these findings were expected. "Even though FDA-authorized vaccines are highly effective, breakthrough cases are expected, especially before population immunity reaches sufficient levels to further decrease transmission," the report says. "However, vaccine breakthrough infections occur in only a small fraction of all vaccinated persons and account for a small percentage of all COVID-19 cases."

Infectious disease experts say the findings are promising.

“These findings indicate that the vaccines are working exactly as advertised and that they are spectacularly successful,” Dr. William Schaffner, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Yahoo Life. “We have to remember what the vaccines were designed to do — to keep us out of the hospital. They're doing that with enormous success.”

The report also shows that “when breakthrough infections occur, they almost always do not have major clinical significance, requiring someone to be hospitalized — an event not expected to be undercounted,” infectious disease expert Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, tells Yahoo Life.

Schaffner points out that the vaccines aren’t perfect and, because of that, some breakthrough infections can occur. “At their best, the vaccines are 95 percent effective,” he says. “Nobody said they would be 100 percent effective — that’s almost impossible, biologically speaking.” Still, he says, the data shows that “this is a very good record.”

Adalja agrees. “These vaccines against COVID are some of the best that we have ever seen,” he says. “The rare breakthrough infections do not change that fact.”

On May 1, the CDC transitioned from monitoring all breakthrough COVID-19 cases to monitoring only those where patients were hospitalized or died, a move that Adalja believes is wise. “It’s important to shift from looking at cases to only looking at serious disease, as the vaccination of high-risk individuals has decoupled cases from hospitalizations and deaths — what flattening the curve was initially about,” he says.

Many of those who were hospitalized and died from a breakthrough infection were elderly or immunocompromised, and Schaffner says that that confirms the notion that people who fall into those categories “should take the belt-and-suspenders approach” because their immune systems don’t respond as well to the vaccine. His recommendation: “Get vaccinated, wear a mask, avoid large groups and continue to be careful.”

Dr. John Sellick, an infectious disease expert and professor of medicine at the University at Buffalo, tells Yahoo Life that the average person shouldn’t worry about breakthrough infections. “For those of us who are of average health, are fully vaccinated and don’t have severe underlying medical problems, breakthrough infections are unlikely to be a huge problem,” he says. “But highly immunosuppressed people have to be careful, just in case.”

Schaffner says that this report makes it clear that the COVID-19 vaccine works. “The general public should get vaccinated,” he says. “Shame on everybody who is not vaccinated. The more people who are vaccinated, the fewer breakthrough infections we’ll have because the virus will not be able to find someone to infect. We all should get vaccinated to help.”

Sellick stresses that the breakthrough cases are “not surprising.” He adds, “I don't think this is going to slow down our progress in the pandemic.”

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