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Covid-19 Breakthrough Infections Can Happen, But Are Less Likely To Be Serious, CDC Chief Says

This article is more than 2 years old.
Updated Apr 22, 2021, 10:44am EDT

Topline

Fully vaccinated people who still contract Covid-19 are believed to be “less symptomatic and less likely to transmit” the virus as more data on those cases comes in, Centers for Disease Control and Prevention director Dr. Rochelle Walensky said Thursday, further underscoring the efficacy of the Covid-19 vaccine even as rare breakthrough infections are reported.

Key Facts

Data increasingly suggests that of those who contract Covid-19 despite being fully vaccinated, approximately a third are “completely asymptomatic,” Walensky said on the TODAY show Thursday, and “many of them have such low virus that they can’t transmit to others.”

While early signs are encouraging, more data is still needed to fully determine whether fully vaccinated people are still able to spread the virus to others, Walensky said, and CDC guidance instructs people to wear face masks even if they’re fully vaccinated while the evidence is still unclear.

The CDC has reported just 5,814 breakthrough infections as of April 13—a number the CDCs acknowledges is an underestimate, but is still only 0.008% of the more than 75 million total vaccinations that took place by that date.

Of those breakthrough infections, the CDC reports 29% were asymptomatic.

A study published Wednesday in the New England Journal of Medicine similarly reported only two breakthrough infections among 417 people studied.

Crucial Quote

“No vaccine is perfect, and so ultimately this is going to be a matter of risk,” Walensky said Thursday. “But what I can say is a 95% effective vaccine is extraordinarily effective. If we can have a 95% effective vaccine and we can get our caseloads down, then we’ll be in really good shape as a country.”

Key Background

Breakthrough infections are possible with any vaccine, and Dr. Anthony Fauci noted during a recent White House Covid-19 briefing that “in the real world, no vaccine is 100 percent efficacious or effective, which means that you will always see breakthrough infections regardless of the efficacy of your vaccine.” Every Covid-19 vaccine approved for use in the U.S. is considered to be broadly effective and protective against severe illness and death. Breakthrough infections take place either when the body cannot mount an “adequate immune response” to the virus or if the vaccine fades over time, Fauci noted, though “even if a vaccine fails to protect against infection, it often protects against serious disease.” The White House is investing more resources in studying breakthrough infections as more people are vaccinated, with part of a $1.7 billion fund for studying the virus and its variants allocated in the American Rescue Act going to surveilling breakthrough infections.

What We Don’t Know

How well the vaccine will protect against emerging coronavirus variants and whether they will make breakthrough infections more likely. While the vaccines are shown to be at least somewhat effective against many of the current variants, the virus may continue to mutate and result in coronavirus variants that are more capable of evading the vaccine, which is why public health officials urge people to continue social distancing in order to bring the infection rate down and keep the virus from further spreading.

Further Reading

Only 2 'breakthrough' infections among hundreds of fully vaccinated people, new study finds (CNN)

CDC Identifies Small Group of Covid-19 Infections Among Fully Vaccinated Patients (Wall Street Journal)

The shock and reality of catching COVID-19 after being vaccinated (Kaiser Health News)

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