What to Know About Breakthrough COVID-19 Cases

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In recent weeks, as cases of the delta variant have increased dramatically in the United States, there’s been talk about “breakthrough” COVID-19 cases but not as much discussion about what these cases actually mean.

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To get to the bottom of what COVID-19 breakthrough cases actually are, how many breakthrough cases there are and what this means for the COVID-19 vaccines, we talked to infectious disease expert Steven Gordon, MD.

What is a breakthrough COVID-19 case?

According to the CDC, a “breakthrough” case is when a person tests positive for COVID-19 at least two weeks after becoming fully vaccinated (either receiving a one-dose vaccine or the second dose of a two-shot vaccine). This is, as the CDC also notes, to be expected. While the COVID-19 vaccines are highly effective at delivering immunity, no vaccine is 100% effective.

But another goal of vaccination is preventing serious illness. And in that regard, the COVID-19 vaccines are successful.

What are the symptoms of a breakthrough case?

The symptoms of a breakthrough case are the same as with typical COVID-19 cases. Most breakthrough cases, though, are either asymptomatic or have symptoms that are less severe than cases in unvaccinated patients.

Those symptoms can include:

  • Fever or chills.
  • Cough.
  • Shortness of breath or difficulty breathing.
  • Muscle or body aches.
  • Headaches.
  • New loss of taste or smell.
  • Sore throat.
  • Congestion or runny nose.

How many breakthrough cases are there?

Because vaccine recipients are far less likely to experience serious illness, the CDC isn’t tracking every breakthrough case. The CDC itself admits that the total number of breakthrough cases that are reported to the organization represents an “undercount” since many breakthrough cases are asymptomatic or mild and aren’t reported by the patients.

But the CDC is keeping track of one important metric with regards to breakthrough cases. “The CDC is now primarily focusing on those breakthrough cases that result in hospitalization or death,” says Dr. Gordon. “And that number is incredibly small.”

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The CDC has created a database to track these cases. So far, the rate of fully vaccinated Americans who have experienced a breakthrough case resulting in hospitalization or death has remained below 0.01%. That doesn’t mean vaccinated people can’t experience a breakthrough case or symptoms. However, the chances of this happening, especially serious illness, still remain far lower as compared to unvaccinated people.

Is the delta variant causing breakthrough cases?

While most current breakthrough cases are from the delta variant, it’s important to note breakthrough cases can come from all COVID-19 variants.

“The delta variant makes up the majority of breakthrough cases in the United States right now because it’s the dominant strain in the country,” Dr. Gordon points out. According to the CDC, the Delta variant made up only 10% of U.S. cases at the beginning of June. But by mid-July, just six weeks later, the Delta variant accounted for over 83% of U.S. cases.

This is because the delta variant is far more transmissible than previous variants of the COVID-19 virus, according to preliminary studies. One study out of China claims the delta variant viral load is 1,000 times higher than the initial strains at the beginning of the pandemic. The higher the viral load, the more likely the person carrying the virus is to spread it to others.

Underscoring the highly contagious nature of the delta variant is a UK study on household transmissions that found a 64% increase in the likelihood of infections compared to the alpha variant (also known as the UK variant which itself was more transmissible than the original variants).

Even though the delta variant is more transmissible, though, Dr. Gordon notes, “At this point, cases from the delta variant haven’t proven to cause more serious illness than other variants.”

What to do if you get a breakthrough COVID-19 case

If you or someone in your home gets sick with a breakthrough COVID-19 case, the best course of action is to isolate as much as possible. This is especially true if anyone in your home hasn’t been vaccinated. While the odds are low that you would infect a vaccinated member of your household, the possibility still remains. If isolation isn’t possible, try to keep air circulating as much as possible and wear masks indoors.

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The CDC currently says that patients who self-isolate are okay to end that isolation 10 days after the onset of symptoms and, if you have a fever, 24 hours after it breaks.

The good news is, as Dr. Gordon points out, breakthrough cases for vaccinated individuals are rarely serious and usually relatively mild. And that underscores why it’s so essential that every eligible person get vaccinated.

The importance of getting the COVID-19 vaccine

The highly transmissible nature of the delta variant proves the importance of getting fully vaccinated against COVID-19. “The vaccines that are available here in the United States are effective against all variants of concern to date, including the delta variant,” says Dr. Gordon. 

That means getting both doses of the two-shot mRNA vaccines (Pfizer and Moderna) so you’re fully protected. While studies cited by the CDC showed the effectiveness of just one shot of Pfizer was between 60% and 80%, getting both shots boosted that rate of protection to over 90%. The Moderna vaccine had a similarly high rate above 90% with both doses.

“Even with those variants of concern, the most important tool we have for prevention of getting an infection is getting vaccinated,” Dr. Gordon says.

“Throughout the pandemic, we’ve talked about flattening the curve so we don’t overwhelm the healthcare system with sick people,” he adds. “And the vaccine has effectively done that. These recent spikes are among the unvaccinated, not among people who are fully vaccinated.”

Even if you’ve received the vaccine and still don’t feel particularly safe or live in an area with a high rate of cases, Dr. Gordon says the best course of action is to keep wearing masks. “You can cut down on those risk factors by wearing masks, especially indoors with other people around,” he says. “But the bottom line is still to make sure, first and foremost, you get fully vaccinated.”

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