(WETM/AP) – As health officials push to get all Americans vaccinated, there is a new concern: breakthrough infections. Fewer than 6,000 COVID-19 infections among vaccinated Americans have been reported so far, but the Centers for Disease Control and Prevention says they believe this number is an undercount.

“You may have immunity to prevent against infection, but you in fact can still get sick with the COVID-19 virus,” Dr. Nistico, infectious disease expert at Arnot Health, said.

Doctors say the breakthrough infections and increased case numbers nationwide are caused by the delta variant, which is different from the COVID-19 strain from 2020. This version is highly transmissible and spreads rapidly. Those who swab positive but are vaccinated are seeing small traces of the virus in their noses, but it is not spreading to the lungs. Some experience mild symptoms, but many are asymptomatic. Health experts say this is a good sign that the vaccine is working at preventing severe disease, hospitalization, and death.

“When you get a vaccine, you reduce your risk of severe infections or reduce your risk of contracting it [COVID],” Dr. Nistico continued. “It’s not to completely eliminate it. It’s very difficult sometimes to do that because everybody’s immune system responds differently.”

Many believe that even amid the delta variant, those who were vaccinated, but still contracted COVID, are less likely to be admitted to the hospital.

“I don’t think we will see significant numbers of people who are vaccinated end up in the ICU,” Dr. John Moore, professor of immunology at Weill Cornell Medicine, added.

Locally, this holds true. Guthrie Health is reporting very few infections among vaccinated residents. Those that are extremely sick typically are unvaccinated.

“If you’re vaccinated, it is exceedingly unlikely that you are going to become infected enough that you need to be admitted to the hospital, go to the ICU, or die,” Dr. Jon Rittenberger, chief of emergency medicine at Robert Packer Hospital, continued.

The cause of these breakthrough infections is likely the new variants, which can pass from person to person more quickly. The virus will continue to mutate to survive, as it has done for the better part of the last two years.

“Less of a virus in the community, there’s going to be less of these occurrences where there are mutations,” Dr. Nistico continued.

Despite these infections, doctors and medical experts remain confident in the vaccinations, saying it is the best tool to fight this pandemic.

“The more people we get vaccinated the better able we will be at preventing the spread,” Dr. David Topham, director of translational immunology and infectious diseases institute at the University of Rochester, concluded.

What is a COVID-19 vaccine “breakthrough” case?

It’s when a fully vaccinated person gets infected with the coronavirus.

In studies, the two-dose COVID-19 vaccines by Pfizer and Moderna were around 95% effective at preventing illness, while the one-shot Johnson & Johnson shot was 72% effective, though direct comparisons are difficult. So while the vaccines are very good at protecting us from the virus, it’s still possible to get infected with mild or no symptoms, or even to get very sick.

If you do end up getting sick despite vaccination, experts say the shots help reduce the severity of the illness — the main reason to get vaccinated.

But the understanding of how vaccinated people who are infected might spread the virus to others is changing.

Previously, health officials believed vaccinated people who get breakthrough infections were unlikely to spread the virus. But with the more contagious delta variant that is now dominant, the U.S. Centers for Disease Control and Prevention said new data shows people who get infected could carry enough virus in their noses and throats to spread it to others.

The agency recently cited the data in updating its guidance to say vaccinated people should go back to wearing masks indoors in areas where the virus is surging.

“It is concerning enough that we feel like we have to act,” said CDC Director Dr. Rochelle Walensky.

Still, health experts say vaccines provide strong protection against serious illness. In the U.S., people who weren’t vaccinated make up nearly all hospitalizations and deaths from COVID-19.