People with breakthrough COVID-19 cases might not spread the coronavirus as much as we think, as new research suggests transmission risk is low among breakthrough cases.

Breakthrough cases happen when someone who is fully vaccinated against COVID-19 becomes infected with the coronavirus. Most of these cases tend to lead to less severe symptoms and hospitalization, resembling a common cold more than anything.

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Ross Kedl, an immunologist at the University of Colorado School of Medicine, told NPR that the virus that comes from a vaccinated person will look different than one from an unvaccinated person.

  • Vaccinated people often have antibodies from the vaccine. These antibodies “should be coating that virus with antibody and therefore helping prevent excessive downstream transmission,” Kedl told NPR.

In fact, Kedl said most vaccinated people appear to be infected by unvaccinated people, at least according to case studies that have come out.

  • “In all these cases where you have these big breakthrough infections, there’s always unvaccinated people in the room,” he told NPR.

Breakthrough cases are becoming increasingly more common among the fully vaccinated, especially because of the highly transmissible delta variant of the coronavirus.

In fact, breakthrough cases are likely to impact thousands of people in the future. Amesh Adalja, a doctor and infectious disease specialist at Johns Hopkins Center for Health Security, told Roll Call that most people will be infected with COVID-19 at some point in their lives.

  • “It’s likely that everybody will probably get infected with COVID-19 (at some point) because it’s an endemic respiratory virus. The goal is to make sure that at that time, that infection occurs after you’ve been vaccinated so it’s mild,” Adalja told Roll Call.

Overall, breakthrough cases remain rare. Unvaccinated people are still at the highest risk of getting infected with the coronavirus. In fact, the Centers for Disease Control and Prevention released data that showed unvaccinated people are five times more likely to be infected with the coronavirus and they have more than 10 times higher chance of dying from COVID-19, according to the CDC.