What to Know About COVID-19 Breakthrough Infections as Omicron Cases Rise

A growing number of people are testing positive after being fully vaccinated—often with mild or no symptoms.

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COVID-19 breakthrough infections are once against on the rise thanks to the spread of the Omicron variant. While exact numbers aren’t publicly available, the highly infectious variant has now spread to the majority of states in the U.S., just weeks after the World Health Organization (WHO) named it a variant of concern.

Stories of vaccinated COVID-19 cases are popping up all over the country. Cornell University recently moved its finals online and urged undergraduate students to leave campus after seeing a jump in breakthrough cases among its students. The school has a 97% vaccination rate, but still saw 1,082 new COVID-19 cases from December 8 through December 14. Early lab results suggest that the Omicron variant is behind the jump in cases, Cornell president Martha E. Pollack said in a message to the school community. School vice president Joel Malina told NPR that “virtually every case” has been in fully vaccinated students.

A report from the Centers for Disease Control and Prevention (CDC) on early Omicron cases in the U.S. found that 79% of the 43 cases detected during the report period were in those who were vaccinated against COVID-19.

Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York, says that “there is zero doubt” that more breakthrough infections will happen as a result of the spread of the Omicron variant. “We’re already seeing this happen,” he adds.

“Breakthrough infections will become much more common with the Omicron variant of COVID,” agrees infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security.

The CDC currently recommends that everyone ages 18 and up who has received the two-dose mRNA vaccines from Pfizer or Moderna receive a third booster shot, citing Omicron as part of the reasoning (along with waning immunity). Those who received the Johnson & Johnson vaccine are urged to get a second shot within two months of their first shot.

It’s hard to know exactly how many breakthrough infections are happening. The CDC stopped tracking the total number of breakthrough cases in the U.S. in May, choosing instead to focus specifically on cases in people who are hospitalized or had died following a breakthrough infection. Now, the CDC has stopped publicly sharing data on all breakthrough infections. Current publicly-available data only shows cases through October, but clearly show that people who are unvaccinated have a much higher risk of contracting COVID-19 than those who are fully vaccinated.

But it’s also clear that breakthrough infections will continue to be a hot topic as new, highly infectious variants like Delta, which is still responsible for a majority of COVID-19 cases in the country, and Omicron continue to emerge and cause a surge in hospitalizations.

What is a COVID-19 breakthrough infection?

According to the CDC, a breakthrough case is defined as someone who has detectable levels of SARS-CoV-2, the novel coronavirus, in their body at least 14 days after they’ve been fully vaccinated against COVID-19, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

The two-week marker is important, Dr. Adalja says. Your body should have enough time to develop antibodies to SARS-CoV-2 after that timeframe. Before then, you won’t necessarily have the built-up immunity you need to fight off an infection. “Cases that occur before [the two-week mark] are not breakthrough cases,” Dr. Adalja says.

Why do breakthrough COVID-19 cases happen?

“These vaccines that we’re using are fabulous but they’re not perfect,” Dr. Schaffner says.

Experts expect for some people to still test positive after being fully vaccinated because “no vaccine has 100% efficacy,” Dr. Adalja says. So far, most people with a breakthrough infection have presented with manageable symptoms.

Think of it this way: Breakthrough cases of COVID-19 can be compared to what someone who gets the flu shot might experience. “Some people can still get the flu after being vaccinated against influenza, but almost invariably that illness will not cause hospitalization,” Dr. Schaffner says.

The makeup of the Omicron variant also seems to raise the risk of a breakthrough infection. The WHO pointed out in late November that this particular strain has several mutations on its spike protein, which is what the virus uses to latch onto your cells and make you sick, that seem to make it more infectious. It also seems to have the ability to at least partially evade the efficacy of our existing COVID-19 vaccines, as early data has shown. (Worth noting: Data has also shown that getting a booster dose of the vaccine does seem to help provide more protection.)

That’s why experts still stress the importance of vaccination and boosters, if you’re eligible, despite the small risk of breakthrough COVID-19 infections. “Even the term ‘breakthrough; gives the wrong impression, as if the vaccine failed,” Dr. Adalja says. “Breakthrough infections were expected to occur and the goal of the vaccine was to make [the infection] mild, which it is.”

What are the symptoms of breakthrough COVID?

This is a little tricky to pinpoint, given that everyone and their immune systems are slightly different. As a general rule, they tend to be milder, Dr. Russo says. The CDC report on Omicron specifically found that most people with breakthrough cases had the following symptoms:

  • Cough
  • Fatigue
  • Congestion
  • Runny nose

    People who are immunocompromised, elderly, or who have serious underlying health conditions could have more severe symptoms, Dr. Russo says. But, Dr. Adalja says, “severe breakthrough infections are rare.” He adds, “breakthrough infections have a range of symptoms, with many people who have no or little symptoms at all.”

    How to protect yourself from a breakthrough infection

    If you’re fully vaccinated and boosted, and concerned about your risk of a breakthrough infection, there are a few things you can do to minimize exposure—and you’re probably already used to most of the precautions.

    Wearing a mask is proven to help protect both the wearer and the people around them, regardless of vaccination status, says Richard Watkins, M.D., an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University. He recommends masking up when you’re in public indoor spaces, such as the grocery store or on public transportation, and “when you’re outside around crowds,” like at a large concert.

    Social distancing is also important. “We’ve become very lax with that,” says Dr. Schaffner. Want to have other fully vaccinated people over to your place? He says it’s safest to gather outside, “but if they’re fully vaccinated and boosted, and you have confidence that they’re reasonably careful out there, you can have a small party”—aim for less than 30 people if possible, he says.

    What should you do if you think you might have COVID-19 after being fully vaccinated?

    If you start to feel unwell, the CDC recommends getting tested for the virus, quarantining until you get your results, and isolating for 10 days from the day you developed symptoms if you have a positive result. If you have a known exposure to the virus, the CDC recommends getting tested three to five days after your exposure and wearing a mask in indoor settings for 14 days or until you receive a negative test result.

    Again, if you develop a breakthrough infection, the odds are high that it will be a mild case. But Dr. Russo says it doesn’t hurt to alert your doctor, especially if you have an underlying health condition that could qualify you for monoclonal antibody treatment. You can also get an at-home pulse oximeter to monitor your blood oxygen levels and talk to your doctor about what should prompt you to seek medical attention. Still, “the chances are, it will be mild and over-the-counter fever reducers and anti-inflammatories may be all one needs,” Dr. Adalja says.

    If you haven’t been vaccinated against COVID-19, medical experts strongly recommend that you get your dose as soon as you can or as soon as you are eligible. Even though the available vaccines do not offer “perfect” protection, the experts we talked to say they so far do an “outstanding” job at preventing severe cases of COVID-19.

    This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.

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