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8 Things You Must Know About Breakthrough COVID-19 Infections

Catching the coronavirus after being fully vaccinated is unlikely, but it happens

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"Breakthrough” is the new pandemic buzzword. Reports of Americans testing positive for COVID-19 despite being fully vaccinated have been making headlines lately — from the halls of Congress to Yankee Stadium to summer celebrations at the tip of Cape Cod. But are these cases, which seem to be popping up more frequently, cause for concern?

Here's what the experts have to say about breakthrough infections.

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1. Breakthrough cases are normal

No vaccine is 100 percent effective at preventing disease. But the shots authorized in the U.S. to help quell COVID-19 are pretty close — especially when it comes to thwarting severe illness and death, which is what they were designed to do.

In fact, less than 1 percent (about 0.004 percent) of fully vaccinated individuals have been hospitalized with, or have died from, COVID-19, according to the latest data tracked by the Centers for Disease Control and Prevention (CDC). When it comes to older adults, who were hit hardest by the coronavirus during its initial sweep, fully vaccinated individuals ages 65 and up are 94 percent less likely to be hospitalized with COVID-19 than people of the same age who are not vaccinated.

And while the CDC no longer tracks how many vaccinated individuals come down with an asymptomatic or mild case of COVID-19 — the more likely scenario if you do get a breakthrough infection — it's safe to assume the risk is also on the smaller side, explains Christopher Ohl, M.D., professor of infectious diseases at the Wake Forest School of Medicine. “It's not common, but it happens,” he says. (New data analyzed by the Kaiser Family Foundation confirms this.) 

The important thing to keep in mind is that when these cases occur, “by no means does that mean that you're dealing with an unsuccessful vaccine,” Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, said in a recent press briefing. “The success of the vaccine is based on the prevention of [more serious] illness.”

2. Delta variant is partially to blame

Breakthrough infections could become more prevalent, however, as the highly contagious delta variant continues to blaze through unvaccinated communities. (About half of the country is not fully vaccinated.)

That's not because the vaccines don't work against the now-dominant strain, which is responsible for more than 80 percent of new COVID-19 cases in the U.S. Studies show that while the immune response is somewhat diminished against delta compared to other virus variants, the vaccines are still holding their ground when a full dose regimen is completed. Rather, it has to do with frequency of exposure.

"Think of the vaccine as reducing your risk of getting infected in any given encounter by something like 90 percent,” says David Dowdy, M.D., associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. If you're in a situation where there are more cases of COVID-19 and you're having closer interactions with people, “then we expect more breakthrough infections — not because the vaccines aren't working but just because people are being exposed [to the virus] more often,” he adds.

Leana Wen, M.D., an emergency physician and visiting professor of health policy and management at George Washington University's Milken Institute School of Public Health, has likened the vaccines to a very good raincoat. “If it's drizzling outside, you're going to be fine; you will be protected and not get wet. However, if you keep going in and out of thunderstorms, at some point you could get wet,” she told AARP in a recent interview.

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3. People with breakthrough infections can spread COVID

If you do get a breakthrough infection, new research suggests it is possible for you to spread the virus to others, even if you don’t get sick with symptoms, yourself.  

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Data from an outbreak investigation released by the CDC on July 30 found that vaccinated people infected with the delta variant have similar viral loads (a measure of the amount of virus in the body) as unvaccinated individuals. And “high viral loads suggest an increased risk of transmission,” CDC Director Rochelle Walensky said in a July 30 statement. 

This new finding is part of the reason why health officials are now recommending that fully vaccinated people wear a face mask in indoor public settings, especially in areas where coronavirus cases are spreading at high or substantial rates. “The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones,” Walensky said.

4. ‘Return to normal’ adds to breakthrough risk

As Americans both vaccinated and unvaccinated return to the workplace and resume pre-pandemic activities, there are more opportunities to be exposed to the coronavirus. In many regions of the country, the numbers bear out the consequences.

As of Aug. 3, about 80 percent of U.S. counties are experiencing high or substantial levels of community transmission. Overall, cases in the U.S. climbed about 64 percent between the week of July 19 and the week of July 26; an average of more than 72,000 infections are now being reported daily, CDC data show. (A month ago, this number was closer to 15,000; at the peak of the pandemic, average daily case counts registered above 200,000.)

Complicating matters is the easing of prevention measures. Practices that had been in place — masks, physical distancing, restrictions on indoor gatherings and so on — have been curtailed or abandoned by many.

“Three, four months ago, people were still being very cautious about this virus. Whereas now, many people are acting a lot less cautiously,” Dowdy says.

Even without delta in the mix, Ohl says, we'd likely still be seeing a rise in breakthrough cases this summer amid the return to pre-pandemic behavior and stalled vaccination efforts. “It wouldn't be quite as many, but it would still be happening,” he says, “just because we're not taking any precautions."

The CDC’s new mask guidelines for vaccinated individuals may help curb these rising rates. The health agency is also recommending that teachers, students, staff and visitors at schools mask up as in-person learning resumes, regardless of vaccination status.

5. Link between breakthrough cases and long COVID is unclear

Millions of people who have had COVID-19 have also reported lingering symptoms, ranging from shortness of breath to difficulty thinking to joint and muscle pain. It's become such a common effect of the disease that clinics have popped up all over the country to study the phenomenon and help these patients get back to normal.

But it's still unclear whether a breakthrough coronavirus infection can result in what's commonly referred to as “long COVID.” Fauci said in a July 22 briefing that it's “an object of a very intensive study right now.”

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A small study out of Israel published in the New England Journal of Medicine found that among 39 healthcare workers with breakthrough infections, 19 percent experienced symptoms that lasted more than six weeks.

However, some experts are betting that the odds of developing long COVID after you're fully vaccinated are slim. “There's good reason to believe that the more serious your infection is, the greater risk you are of having longer-term sequelae” — a word that refers to a condition resulting from an illness, Dowdy says.

"And since the vaccines are particularly good at preventing infections from getting out of hand when they do occur, there's strong reason to believe that these vaccines will also be very effective in preventing these sorts of long-term sequelae,” he adds. 

6. Older adults are bearing the burden of serious breakthrough cases

While less than 1 percent of breakthrough cases have resulted in hospitalization or death, older adults make up the majority of those impacted by these severe infections. CDC data show that nearly three-fourths (74 percent) of people who have been hospitalized or have died from COVID-19 after being fully vaccinated have been adults 65 and older.

7. Testing is critical as cold and flu season looms

If you are fully vaccinated and start to feel ill, getting a test to determine the cause is increasingly important — especially with colds on the rise and flu season right around the corner, Ohl says. If it's the flu, there's antiviral medicine that can help relieve symptoms. (Currently, there is no easy-to-prescribe pill to treat COVID-19, but there could be soon.)

If it's COVID-19, “you're going to need to isolate and take precautions to not give it to other people, particularly vulnerable people,” Ohl says. "And if it's a cold, then you can just do what you normally would do with a cold. So you kind of need to know what's causing these mild symptoms.” 

8. Vaccines provide best protection

The best way to protect yourself from getting COVID-19 is to get vaccinated. And as more people roll up their sleeves to get the shots, we'll likely start to see fewer breakthrough infections.

"Largely, the breakthrough infections come from a vaccinated person being exposed to an unvaccinated person who has COVID,” Ohl says. “Think of it like we're going to have the virus do a mud run. ... The more people that get vaccinated, the thicker and deeper the mud is, and the likelihood of the virus being transmitted between people gets less and less and less.”

In the meantime, as new cases of COVID-19 shoot up across the country, “there is a reason for us all to be a bit more cautious about things,” Dowdy says.

"The number one message that people need to hear is that these vaccines still work. They work against the delta variant, and it's the best mode of protection anyone has when it comes to getting this disease,” he adds. However, “if case counts continue to go up, don't consider yourself 100 percent protected."

Editor’s Note: This story, originally published Aug. 3, has been updated to reflect new information.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.

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