COVID-19 Breakthrough Infections: 3 Things to Know

Cases of COVID-19 are surging again in the United States, overwhelmingly among people who are not vaccinated against the disease. This latest surge is caused by the delta variant, a version of the COVID-19 virus that is more transmissible than prior variants. With the delta variant, fully vaccinated people can experience what are sometimes called “breakthrough infections,” which means they test positive for COVID-19.

Stories about breakthrough infections are causing a lot of worry about whether the vaccines hold up against the hyper-transmissible delta variant. We asked UNC Health infectious diseases specialist David A. Wohl, MD, what we need to know.

1. “Breakthrough” is a misnomer.

The term “breakthrough” to describe what occurs when you catch the virus even though you’ve been vaccinated is misleading. That is because vaccines are intended to prepare your immune system to fight germs once they enter your body. In the case of COVID-19, the vaccines do not prevent the virus from getting into your nose or throat, but they do make sure the immune system can protect you from getting sick.

That explains why the vast majority of these breakthrough cases are mild or even asymptomatic (no symptoms). In contrast, virtually all of the recent COVID-19 admissions to intensive care and deaths are among the unvaccinated.

“Vaccines are not a force field that protects you from the virus coming into your body,” Dr. Wohl says. “The virus can find its way into your nose like we have seen in some of these baseball players or Olympians, but if you are vaccinated, it is unlikely to make you very sick.”

Instead, in those who are vaccinated, the vaccine-primed immune system prevents the virus from getting a foothold in the lungs and causing pneumonia.

“For the vaccinated, COVID-19 is becoming more of a nuisance than it is a threat. But, for the unvaccinated, the delta variant remains dangerous, especially, but not only for those with risks for severe COVID-19,” Dr. Wohl says.

2. It’s hard to know how many people will have a breakthrough infection.

Because most people are not tested regularly for COVID-19, it’s hard to determine how many breakthroughs will occur. Plus, it is likely that many of those who are vaccinated and become infected with the COVID-19 virus have little or no symptoms.

Think of it this way: If you’re vaccinated for COVID-19 and get infected with the virus, but thanks to your vaccine you have no symptoms and never get tested, you’ll never know.

But, we are learning that even vaccinated people can harbor the virus in their noses and throats and shed it, possibly infecting others. That’s why vaccinated as well as unvaccinated people are being encouraged to wear masks inside public places where transmission rates are high.

“The delta variant leads to a lot more virus being present in people’s upper respiratory system—even those who are vaccinated. But they may not know it,” Dr. Wohl says. “This is why masking is really important now, during this surge. Since the vaccinated are really unlikely to become sick if they catch the COVID-19 virus, they can still pass it on unwittingly.”

3. The vaccines are highly effective against serious complications and death.

The COVID-19 vaccines have been very effective in preventing severe infections and death, even against the delta variant.

“There has absolutely not been a massive breakdown in the protection offered by the vaccine; in fact, it is the opposite. We’re seeing the vaccines really hold up well against the delta variant—protecting the vaccinated from ending up in the hospital or worse,” Dr. Wohl says. “Remember, vaccines aren’t meant to completely prevent infection or even mild cases. The No. 1 goal of any vaccine is to keep you from getting very sick and needing to go to the hospital or dying if the virus enters your body. The vaccines are still doing exactly what we want them to do, which is protecting us at a high level against bad things happening to us.”

Recent studies looking at how well the antibodies of vaccinated people fight the delta variant suggest that all three vaccines available in the United States will protect against this virus. Also, a report from Public Health England found two doses of the Pfizer vaccine to be 96 percent effective against hospitalization for the delta variant in the United Kingdom, where nearly all COVID-19 cases are now caused by the delta variant. That means almost everyone hospitalized with COVID-19 was not vaccinated. Similar trends are being observed here in the United States.

The delta surge has led not only to more cases but also more hospitalizations. Deaths are also trending up. With higher rates of vaccination, fewer people would become severely ill or die.

“Back in the olden days of the summer of 2020, we talked about how if we had a vaccine that was 50 percent effective, we would be really fortunate. And we have vaccines that have much greater effectiveness than that,” Dr. Wohl says. “The vaccines are doing what we need them to do.”

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