FILE - In this Monday, July 12, 2021, file photo, Karen Martin receives a COVID-19 vaccine at a vaccination clinic hosted by James River Church West Campus in conjunction with Jordan Valley Community Health Center in Springfield, Mo. COVID-19 cases have doubled over the past three weeks, driven by the fast-spreading delta variant, lagging vaccination rates in some states and Fourth of July gatherings. The five states with the biggest two-week jump in cases per capita all had lower rates, Missouri, 45.9%; Arkansas, 43%, Nevada, 50.9%, Louisiana, 39.2% and Utah, 49.5%. (Nathan Papes/The Springfield News-Leader via AP, File)

Reports of people being diagnosed with COVID-19 despite vaccination may sound alarming, but top health experts point to overwhelming evidence that the shots are doing exactly what they are supposed to: dramatically reducing severe illness and death.

The best indicator: U.S. hospitalizations and deaths are nearly all among the unvaccinated.

What scientists call “breakthrough” infections in people who are fully vaccinated make up a small fraction of cases.

“When you hear about a breakthrough infection, that doesn't necessarily mean the vaccine is failing,” Dr. Anthony Fauci, the U.S. government's top infectious disease specialist, told a Senate panel this week. The shots are holding up, he said, even in the face of the highly contagious delta variant that is burning through unvaccinated communities

Health authorities have warned that even though the COVID-19 vaccines are incredibly effective — the Pfizer and Moderna ones about 95% against symptomatic infection in studies — they're not perfect. No vaccine is.

But it wasn't until delta variant began spreading that the risk of breakthroughs started getting much public attention. The barrage of headlines is disconcerting for vaccinated people wondering how to balance getting back to normal with more exposure to unvaccinated strangers — especially if they have vulnerable family members, such as children too young to qualify for the shots.

Sports fans are seeing daily reports about infected athletes, from the New York Yankees to the Summer Olympics. With the Games soon to start, Kara Eaker, a member of the U.S. women's gymnastic team who said she was vaccinated, tested positive in a training camp just outside Tokyo. WNBA player Katie Lou Samuelson pulled out of the Olympics and the 3-on-3 basketball competition after testing positive despite being vaccinated.

And politicians in the nation's capital are being rattled by reports of breakthrough cases, including from Florida Republican Vern Buchanan, some Texas Democratic lawmakers in Washington as a political protest, at least two people in the White House, and several congressional staff members.

One critical question about breakthrough cases is whether the person actually had symptoms, Dr. Francis Collins, director of the National Institutes of Health, told The Associated Press. “Or is this somebody just being sampled out of an abundance of caution because they had to go into some place like the Congress?” he added.

Indeed, the U.S. Centers for Disease Control and Prevention has said for months that vaccinated people don't even need to get tested after a virus exposure unless they develop symptoms.

The agency cites limited evidence that they're less likely to infect others than unvaccinated people who get an asymptomatic infection.

As of July 12, the CDC had tallied 5,492 vaccinated people who were hospitalized or died and also tested positive for coronavirus — out of more than 159 million fully vaccinated Americans.