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Vaccine breakthrough cases rising with Delta: Here’s what that means


Unanswered questions

One of the biggest questions about breakthrough cases is how often people who have it may pass the virus to others.

“We know the vaccine reduces the likelihood of carrying the virus and the amount of virus you would carry,” Dr. Wen told CNN. But we don’t yet know whether a vaccinated person with a breakthrough infection may still be contagious to others.

For that reason, the Centers for Disease Control and Prevention says that fully vaccinated people still need to be tested if they have symptoms and shouldn’t be out in public for at least 10 days after a positive test.

How should fully vaccinated people behave? That depends a lot on their underlying health and whether or not they have vulnerable people around them.

If you’re older or immunocompromised, Dr. Schaffner recommends what he calls the “belt-and-suspenders approach,” in other words, do everything you can to stay safe.

“Get vaccinated for sure, but since we can’t be absolutely certain that the vaccines are going to be optimally protective and you are particularly susceptible to serious disease, you would be well advised to adopt at least one and perhaps more of the other mitigation measures,” he said.

These include wearing a mask, social distancing, making sure your spaces are well ventilated, and not spending prolonged periods of time indoors in crowded places.

Taking young children to visit vaccinated, elderly grandparents demands extra caution, again, with Delta circulating, particularly as they go back to school and start mixing with other kids.

Dr. Schaffner recommends explaining the ground rules before the visit: Hugs around the waist. No kissing. Wearing a mask while indoors with them.

Other important unanswered questions are whether breakthrough infections can lead to prolonged symptoms, or “long covid.” Most experts think that’s less likely in vaccinated people.

And Dr. Osterholm said it will be important to see whether there’s anything unusual about the breakthrough cases happening in the community.

“I think some of us have been challenged by the number of clusters that we’ve seen,” he said. “I think that really needs to be examined more.”

A version of this article first appeared on


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