Although COVID-19 vaccines are effective at preventing illness, they don’t provide 100% protection against the virus, meaning that, though the chance is small, a fully inoculated person can get sick.
When a fully vaccinated person tests positive for COVID-19, it’s referred to as a breakthrough case. Health experts say breakthrough cases are rare and are usually mild forms of the illness.
What precautions should you take if you or someone you know has a breakthrough case of COVID-19? Here’s what you need to know.
When do breakthrough cases occur?
Health experts say breakthrough cases, though rare, are not unexpected.
“Just like we have with flu, where if you’re vaccinated some years you get 40%, some years you get 50% protection, you can still get the disease,” said Dr. Marcial Oquendo, a pediatrician and member of the Dallas County Medical Society. “Even with the flu vaccine, there’s lots of other variants going around in any given year. With COVID, we kind of knew that that was going to happen, so it wasn’t a surprise.”
In Dallas County, health officials compare individual-level test and vaccine data to determine how many breakthrough cases have occurred, said Dr. Philip Huang, director of the county’s health department.
More than 1 million people in the county are fully vaccinated, according to state data. As of July 1, there were 955 breakthrough cases in Dallas County, making up about 0.09% of all fully vaccinated people, according to county data.
Of the breakthrough cases, 92 people were hospitalized and 13 died.
Although the county hasn’t yet made more detailed information about breakthrough cases available, Huang said the breakthrough cases that had the most serious outcomes were among people who “were specifically immunosuppressed or on immunosuppressive medications.”
“Persons in those situations, the recommendations are they should talk to their physician about if they are at higher risk,” Huang said. “Even though they have the vaccine, they may still need to be practicing wearing the mask and doing some more protection.”
Health experts say people who fall into that category include organ transplant recipients, people undergoing chemotherapy and people with autoimmune conditions, such as lupus or rheumatoid arthritis, which are treated using medicines that prevent strong immune responses.
“That’s true for the annual flu vaccine, that’s true for the pneumonia vaccine,” said Dr. Mark Casanova, past president of the Dallas County Medical Society. “Any vaccine in an individual who has a blunted or subdued immune response is going to leave them at risk.”
Casanova said breakthrough cases also can happen in individuals who are exposed to COVID-19 before they have developed full immunity.
Because it takes up to two weeks after a person’s final dose for the body to build up full protection, it’s possible someone could be exposed to the virus shortly after the second dose and still get sick.
The Parkland Center for Clinical Innovation, which has tracked COVID-19 data for Dallas County since the beginning of the pandemic, and the county health department have said they expect to have more detailed information about breakthrough cases available in early July.
What should you do if someone in your home has a breakthrough case?
If everyone in a household is fully vaccinated and someone gets a breakthrough COVID-19 case, people don’t have to take the same strict precautions they would have at this time last year, health experts say.
Fully vaccinated people who test positive for COVID-19 should still stay home and avoid group gatherings, according to guidance issued by the Centers for Disease Control and Prevention. They can go back to being around others once they meet the criteria that have been used since the early days of the pandemic.
But health experts said that as long as everyone else in a home is fully vaccinated against the virus, sick people don’t have to totally isolate themselves the way they would have this time last year.
“We try to limit the exposure to that person, but not necessarily in the sense that what we were doing before,” Oquendo said. “Your chances of having breakthrough infections is still very small and very rare. If you have a household of four and one has a breakthrough infection, the chance of someone else having a breakthrough infection in that house would be very, very slim.”
Casanova gave the example of his own household, which includes himself, his wife, their daughter and his father.
If Casanova were to test positive for COVID-19, he would stay away from his family when possible but wouldn’t necessarily confine himself to one room. Instead, he said, he’d wear a mask around his family and wash his hands as much as possible.
“In the early days if I had gotten COVID, I would have stayed in a hotel. I would have totally removed myself from my family, or done something within the house to totally remove myself,” he said. “[Now] I would stick to my room. I’d stay away from my dad because he’s older and frailer, but I wouldn’t be as extreme in my mitigation measures.”
The reason, he said, is because though breakthrough infections are rare, the chance of a vaccinated person passing the virus to another vaccinated person is even rarer.
“Despite the fact I got it, my body is still going to very effectively fight it. My viral load, how much virus I’m going to produce, is very low,” he said. “Low enough that my dad should be OK. That second hop, that hop from me to Dad, is about 0.08% [of a chance]. And even if he happens to be that 0.08%, his case will be extraordinarily low and be probably totally inconsequential.”
Fully vaccinated individuals who are exposed to COVID-19 don’t have to quarantine or get tested for COVID-19 if they aren’t experiencing symptoms, according to guidance issued by the CDC. Instead, they should monitor their symptoms for 14 days after their last exposure.
Health experts say in homes where people are immunosuppressed or where not everyone is fully vaccinated — in homes with children under 12, for example — people should follow the recommendations that were issued before vaccines were available, even in breakthrough cases.
“If you have kids less than 12, technically they still have to do the same rules that we were doing back in March of last year: the social distancing, the masks when you’re in public even when you’re inside, if you’re exposed to someone who’s sick, you need to isolate,” Oquendo said. “Those rules still apply because that person, even if it’s a child who typically tends to not have big, bad infections, they still have to follow the same guidelines that we had last year. The life adjustments are really about people who are fully vaccinated.”