What to Know About Breakthrough COVID-19 Infections

Mini Kamboj, MSK's Chief Medical Epidemiologist

Mini Kamboj, MSK's Chief Medical Epidemiologist

Breakthrough COVID-19 infections are a rare occurrence in people who have been fully vaccinated. Memorial Sloan Kettering Cancer Center Chief Medical Epidemiologist and infectious disease expert Mini Kamboj explains that when these breakthrough infections occur, they are not nearly as serious as COVID-19 infections in people who are unvaccinated.

“Even with the emergence of new variants, we have seen a lot of data that shows the vaccines work and achieve the most important goal: preventing hospitalizations and deaths from COVID-19,” says Dr. Kamboj. “We hope to see this trend continue.”

Here, she answers common questions about breakthrough infections and what they mean for our MSK community.

What is a breakthrough COVID-19 infection?

A breakthrough infection means someone tests positive for the virus after they have been fully vaccinated. No vaccine is 100% effective at preventing infection, so it has not been surprising that some vaccinated people are still getting infected with COVID-19.

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How common are breakthrough infections?

Breakthrough COVD-19 infections are uncommon.

As of November 29, 2021, the New York State Department of Health reported ”179,502 laboratory-confirmed breakthrough cases of COVID-19 among fully-vaccinated people in New York State, which corresponds to 1.4% of the population of fully-vaccinated people 12 years or older.”

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How serious are the symptoms from breakthrough infections?

Individuals with breakthrough infections may have no symptoms and may not even be aware they have the virus. For those who do feel sick, the symptoms are usually mild and last a few days to one or two weeks. These symptoms typically include headache, cough, fever, and fatigue. Serious symptoms are unusual.

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Will the COVID-19 vaccines protect against breakthrough infection?

The COVID-19 vaccines now available were created for the original strain of the virus. We have learned that the vaccines are effective against Delta and other variants, though scientists and doctors are still learning more.

What We Know Now about COVID-19 Variants

Read more »

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Can people with breakthrough infections transmit the virus to others?

Evidence suggests that vaccinated people are less contagious because they have milder illness and shed the virus for a shorter time, but the extent of this difference between vaccinated and unvaccinated people is not definitively known. Until more studies are available, it is wise for everyone — including vaccinated people — to keep washing their hands and wear masks in certain situations.


December 2, 2021


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