December 3, 2021, 22:54

Why breakthrough COVID-19 infections don’t mean the vaccine isn’t working

Why breakthrough COVID-19 infections don’t mean the vaccine isn’t working

With more than 161 million people now fully vaccinated in the U.S., experts say we are bound to see reports of breakthrough infections, meaning people test positive for COVID-19 while fully vaccinated.

“When you hear about a breakthrough infection, that doesn’t necessarily mean the vaccine is failing,” Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said before Congress on Tuesday.

COVID-19 vaccines are highly effective, but they do not block the virus 100% of the time, meaning that some breakthrough infections occur after vaccination.

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“I think people need to appreciate when you talk about breakthrough infections that the original data from the clinical trial — the efficacy data was based on preventing clinically apparent disease, not preventing infection, such as a symptomatic infection,” Fauci said.

J. Scott Applewhite/APTop infectious disease expert Dr. Anthony Fauci responds to accusations by Sen. Rand Paul, R-Ky., as he testifies before the Senate Health, Education, Labor, and Pensions Committee, on Capitol Hill in Washington, Tuesday, July 20, 2021. Cases of COVID-19 have tripled over the past three weeks, and hospitalizations and deaths are rising among unvaccinated people. (AP Photo/J. Scott Applewhite, Pool)

Despite many high-profile cases of breakthrough infections with mild or no symptoms, including among Olympic athletes and some politicians, the overall number is very low compared to the number of people vaccinated.

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That doesn’t mean severe illness as the result of an infection isn’t possible, but this tends to happen in people who are elderly or otherwise immune-compromised, experts said.

“Out of 157 million fully vaccinated in the US, there were 4,909 hospitalizations and 988 deaths,” Dr. Carlos del Rio, infectious disease physician and professor of Medicine in the Division of Infectious Diseases at Emory University School of Medicine, said during a press briefing on Monday.

Ezra Acayan/Getty ImagesMANILA, PHILIPPINES – JULY 20: A healthcare worker prepares a shot of Sinovac Biotech’s CoronaVac COVID-19 vaccine during a mass vaccination for public transportation workers on July 20, 2021 in Manila, Philippines. The Philippines, which is currently suffering the second-worst COVID-19 outbreak in Southeast Asia with more than 1.5 million cases and more than 26,800 deaths, is struggling to cope with the demand for vaccines after the health ministry confirmed the presence of the more contagious Delta variant in the country.

“Of course we will see some breakthrough infections that lead to severe illness, more in vulnerable populations with underlying chronic conditions who couldn’t mount a response to vaccines because they couldn’t,” Dr. John Brownstein, an infectious disease epidemiologist at Boston’s Children’s Hospital and an ABC News contributor, told ABC News.

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Although studies on this aren’t completed, Fauci said last week that the risk of a vaccinated person spreading COVID to someone else is assuredly far less than an unvaccinated person spreading COVID.

“You could make a reasonable assumption that the rate of transmissibility from the asymptomatic vaccinated person to an uninfected person would be less likely than if the person was unvaccinated,” Fauci said at a White House COVID-19 Response Team briefing last week.

The overall number of breakthrough infections is rising, but that could be because more people overall are getting vaccinated, resulting in more breakthrough cases, Dr. Shobha Swaminathan, an associate professor and infectious disease expert at the Rutgers New Jersey Medical School, told ABC News.

“As the number of infections in the U.S. increases, there may be a slight increase in the number of ‘breakthrough’ infections,” Swaminathan said. “However, the majority of infections continue to be reported among those who have not been vaccinated.”

Experts said the delta variant could be contributing to these cases, but for now, research is ongoing.

“If it causes an increased rate of breakthrough infections, that’s unknown,” adds Brownstein.

Pool/Getty ImagesWASHINGTON, DC – JULY 20: Rochelle Walensky, Director of the U.S. Centers for Disease Control and Prevention (CDC), left, and Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, listen at a Senate Health, Education, Labor, and Pensions Committee hearing at the Dirksen Senate Office Building on July 20, 2021 in Washington, DC. The committee will hear testimony about the Biden administration’s ongoing plans to deal with the COVID-19 pandemic and Delta variant.

But experts feel reassured by what they do know, that even with the highly-transmissible delta variant sweeping the country, more than 99% of COVID-19 deaths are among people who are unvaccinated.

“In some parts of the country, the percentage is even higher, particularly in areas of low vaccination rates,” Dr. Rochelle Walensky, the director of the CDC, said in a hearing on Capitol Hill on Tuesday. “The best way to stop the spread is with vaccines.”

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