Delta variant: 8 things vaccinated people should know about breakthrough Covid-19

What to understand about this new phase.

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For many Americans, the feeling of freedom after being fully vaccinated was fleeting. We shed our masks, sat inside restaurants, and finally felt like our risk of catching Covid-19 was a thing of the past.

We knew vaccines didn’t promise 100 percent protection but all provided solid protection against symptomatic infection from the original strain of the virus. That’s still largely true.

People who haven’t been vaccinated are much more likely to contract Covid-19 than those who are. But a surge in the Delta variant, which is significantly more transmissible and replicates more in the body, has coincided with an uptick in breakthrough infections — though they are still relatively uncommon. Early research suggests Delta may cause people to be more contagious for longer, regardless of vaccination status.

These events have culminated in new mask guidelines from the Centers for Disease Control and Prevention (CDC): It’s recommended to mask up indoors if you live in an area of substantial or high Covid-19 transmission.

Covid-19 vaccines, meanwhile, still appear to provide excellent protection — especially against hospitalization and death.

Here are eight questions about breakthrough infections answered, including how common they are, who is most likely to be infected, and what breakthrough Covid-19 means for the children of vaccinated adults.

What is breakthrough Covid-19?

The CDC defines breakthrough infections as “the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person ≥14 days after they have completed all recommended doses of a U.S. Food and Drug Administration (FDA)-authorized COVID-19 vaccine.”

In practice, it means that someone is positive for Covid-19 even after the vaccine has gotten enough time to work.

How common are breakthrough infections?

Although the CDC’s information regarding breakthrough infections isn’t exactly comprehensive — they’ve only been monitoring breakthrough infections that result in hospitalization or death since May 1 — preliminary numbers suggest infections are relatively rare.

As of July 19th, more than 161 million people in the United States had been fully vaccinated. Between May 1st and July 19th, the CDC says:

  • 5,601 fully vaccinated people were hospitalized
  • 1,141 fully vaccinated people died

Those who are hospitalized or die are more likely to be older, be immunocompromised, or have preexisting comorbidities. While the study of breakthrough infections is still limited, a May 2021 CDC study found the median age of patients who died between January and April of breakthrough Covid-19 was 82 years old.

Between January 1st and April 30th, 2021, when the CDC was still tracking all breakthrough infections, volunteers reported 10,262 breakthrough infections. In those same months, there was a total of 11.8 million Covid-19 diagnoses.

What are breakthrough Covid symptoms?

Donald J. Alcendor is an associate professor of microbiology and immunology in the Center for AIDS Health Disparities Research at Meharry Medical College. Symptoms of breakthrough Covid infections run the gamut from completely asymptomatic to severe resulting in hospitalization or death, he tells Inverse.

Researchers are still learning about the highly contagious Delta variant.

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In fact, 27 percent of all breakthrough cases reported to the CDC were asymptomatic.

“For people under 65 without comorbidities, breakthrough infections are more likely to be asymptomatic or mild,” Alcendor says. “For people over 65 or with a compromised immune system, the risk is a bit higher.”

Still, he stresses, the people who remain at the highest risk are those who are unvaccinated. Statistics coming out of hospitals back him up: Approximately 99.5 percent of all people dying from Covid-19 in the United States are unvaccinated.

Can breakthrough cases spread Covid-19?

It’s much more likely with the Delta variant than other variants Alcendor says.

“A [vaccinated] person exposed to the Delta variant is going to have a greater risk of a breakthrough infection, just because it’s more contagious,” he says. “There’s a greater viral load in a person infected with Delta.”

According to the CDC:

“A growing body of evidence indicates that people fully vaccinated with an mRNA vaccine (Pfizer-BioNTech or Moderna) are less likely than unvaccinated persons to acquire SARS-CoV-2 or to transmit it to others. However, the risk for SARS-CoV-2 breakthrough infection in fully vaccinated people cannot be completely eliminated as long as there is continued community transmission of the virus.”

Who is most likely to get breakthrough Covid-19?

It depends on what we mean when we say breakthrough Covid-19.

Because the CDC is currently only tracking breakthrough infections resulting in hospitalization and death, we don’t have a clear idea of how many people are getting breakthrough infections that are symptomatic or mild. We do know people over 65 as well as people with compromised immune systems are most likely to have severe illness caused by a breakthrough infection.

“If you're 65 and older, your immune response to the vaccine is somewhat more challenged than say a person that's young, that’s clear,” Alcendor says. Among the breakthrough cases reported to the CDC, 75 percent occurred in people 65 and older.

Breakthrough infections are also more likely in people who are immune-compromised and/or have comorbidities like heart disease or diabetes.

What does Delta mean for kids of vaccinated adults?

It depends on the age group of kids you’re talking about, Alcendor says. Kids over the age of 12 are eligible to be vaccinated and should be if they’re able.

“... the likelihood of transmitting the Delta variant to a child is quite real.”

Kids under the age of 11 aren’t eligible to be vaccinated yet. This means it’s possible for a vaccinated parent to transmit the virus to their unvaccinated child, especially with the Delta variant.

“For other variants and the original virus, it was believed that transmission occurred after about 15 minutes of close contact,” Alcendor says.

“With the Delta variant, it’s a fraction of that,” he says. “So for a parent around a child kissing, hugging, and being in close contact, the likelihood of transmitting the Delta variant to a child is quite real.”

Critically, he notes that children, especially those under the age of 11, are much less likely to have severe illness than adults. While the Delta variant appears to cause more severe disease in everyone, children included, Alcendor says the outcomes for children are still very good.

Fin Gomez, a journalist, replaces a mask-wearing guidance sign at the White House.

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The American Academy of Pediatrics says that between 0.1 percent and 1.9 percent of child cases of Covid-19 result in hospitalizations. Over the course of the pandemic, about 300 children (those under the age of 18) have died. The AAP says of pediatric cases reported by 43 states, between 0.00 percent and 0.03 percent resulted in death.

A small number of children who contract Covid-19 do have other very rare inflammatory or neurological complications, however, so once vaccines are approved for children under 11, it will be important for them to get vaccinated as soon as possible.

What does breakthrough Covid mean for wearing masks?

On Tuesday, the CDC updated its mask guidelines to recommend that unvaccinated and fully vaccinated people wear masks in public spaces.

Specifically, people are advised to resume wearing masks in areas where there have been more than 50 new infections per 100,000 residents in the past week or more than 8 percent of tests are positive for infection over that period. You can track the rates of infection in your county here.

How do masks protect vaccinated people?

The underlying principle of how masks protect people hasn’t changed, even for vaccinated people.

Masks always helped reduce the spread of infection by reducing the number of infectious viral particles an infected person emits into an environment, and consequently the amount of virus an uninfected person is exposed to. While masks protect the unvaccinated, they also protect the vaccinated: Reduced transmission means fewer opportunities for the virus to mutate into something vaccines have more difficulty handling.

Alcendor says with other variants and the original strain, the viral load was so low in unvaccinated people that it made transmission unlikely. Delta changed the game.

Masked attendees at an indoor concert in Germany.

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“The Delta variant is 50 percent more contagious and makes more virus in your system, which increases the chance of transmission,” he says. “Now the Delta variant represents 83 percent of new infections in the United States. What the CDC is saying is that vaccinations are still effective, but we want to keep these new infections as low as possible.”

Ultimately, the more people who get vaccinated, the better off everyone is. Even the polio vaccine didn’t provide 100 percent protection against paralysis. But widespread vaccination still managed to eradicate the disease.

Widespread vaccination also prevents new, dangerous variants like Delta, from developing.

“When you have enough vaccination, the virus has little opportunity to replicate,” Alcendor explains. “It's only when the virus replicates in the body that you have the evolution of variants. That's why variant evolution is directly related to the unvaccinated population.”

So if you hate wearing masks or staying home, get vaccinated and encourage everyone you know to do the same. It’s the best chance we have of preventing more variants.

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