Those fully vaccinated against COVID-19 can be infected, but serious illness is rare: 'Nothing in this world is 100%'

Everyone wants vaccines to be perfect – and the COVID-19 ones nearly are. Only a tiny fraction of those who are vaccinated end up seriously ill from an infection

But still, some fully vaccinated people will get sick, some will pass on the virus, and a very small number will die despite their shots

"The efficacy of the vaccines in preventing hospitalizations and death is unbelievable," said Carlos del Rio, an epidemiologist and distinguished professor of medicine at Emory University School of Medicine in Atlanta. "It's not 100%. But nothing in this world is 100%."

At a time when the infection rate has doubled, many remain unvaccinated and the delta variant is vastly more contagious than the original, it's important to recognize vaccines aren't flawless, he and others said.

"I understand it's kind of a tough pill to swallow for many people," said Anthony Santella, a public health expert at the University of New Haven in Connecticut. 

Several recent high-profile cases have brought public attention to the fact that people who are vaccinated can still catch the virus.

Last Thursday's Yankees-Red Sox game was postponed because six Yankees – most, but not all, of whom were vaccinated – tested positive for the virus. At a homeless shelter in Northern California, a number of vaccinated residents tested positive during an ongoing outbreak. And six vaccinated members of the Texas Legislature, who had fled the state to prevent a vote on changes in the state's election laws, have tested positive for the coronavirus in recent days.

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The common thread for all those infections was that they were caught by routine testing, not because people fell seriously ill, noted Ali Ellebedy, an immunologist at Washington University School of Medicine in St. Louis.

Of the more than 159 million fully vaccinated Americans as of July 12, a reported 5,492 have been hospitalized, and 791 have died related to symptomatic COVID-19, according to the Centers for Disease Control and Prevention.

In May, the CDC stopped tracking all so-called breakthrough infections, focusing only on state and local health department reports of hospitalizations and deaths, so there's no way to know how many infections there have been or whether they are increasing because of the delta variant. 

Dr. Leana Wen, an emergency physician and former Baltimore health commissioner, called that decision “inexplicable.”

Without that data, she said, it’s impossible to know how many people are getting infected after vaccination, whether certain people, perhaps senior citizens, are more vulnerable to breakthrough infections, and how easy it is for people who have been vaccinated and then infected to pass on the infection to others.

“We just don’t know the answers to these questions, and that is really preventing clinicians from giving good guidance to our patients,” she said. 

Breakthrough cases of COVID-19 are growing probably because more virus is circulating, not because vaccines don't work against the delta variant, which now accounts for more than half the infections in the United States, experts say.

Vaccines remain effective against severe disease from the delta variant, said Ellebedy, who studies the body's response to vaccination.

But the variant is vastly more contagious than the original virus, so the unvaccinated are particularly vulnerable.

"If you're vaccinated, you should not worry about the delta variant," del Rio said. "If you're not vaccinated, you are really in trouble because it's likely that you will get infected."

Range of protection

Even healthy people respond differently to vaccination, so it is normal to see variation in protection among the vaccinated, Ellebedy said. 

For 95 people out of 100, vaccines from Pfizer-BioNTech and Moderna will provide effective protection. 

The problem is, it's essentially impossible to figure out ahead of time who is most vulnerable. Certain factors like age, obesity and lung disease increase the risk of serious disease if someone is infected. So does the load of virus they inhale and what medications they're taking, he said. 

Some people will test positive for the virus despite vaccination, but the immune protection they received will keep virtually all those people from getting seriously ill.

People who are fully vaccinated can get COVID, but experts say they're unlikely to get severely ill.

Vaccination also makes people less likely to shed large amounts of virus, Ellebedy said, meaning they are less likely than an unvaccinated infected person to get someone else sick. Anything that decreases the amount of virus replicating itself in the respiratory tract will decrease the probability of passing on that virus, he said. "Transmission will decrease like everything else."

 And though the data remains thin, vaccination also likely protects against long-haul COVID-19, in which people have symptoms weeks or months after they clear their initial infection, said David Holtgrave, dean of the School of Public Health at the University at Albany, State University of New York.

“Long-haul symptoms in persons who are fully vaccinated may be theoretically possible but are likely rare given the overall effectiveness of the vaccines (after being fully vaccinated); however, we could use more data to know that for certain,” he said via email. “That is why we need this more robust national surveillance system.”

A previous coronavirus infection provides some protection against the delta variant, but someone who got COVID-19 months ago might not have enough of an immune response left, del Rio said. 

"My advice if you have been infected, is you should trust your natural immunity for about three months. But after three months, you should get vaccinated," he said.

People who were infected and then vaccinated are probably well-protected. Ellebedy said.

Context also matters, Ellebedy and others said. Someone who is vaccinated and who lives in a community with a high vaccination rate and a low infection rate probably can get away without a mask.

Ellebedy lives in Missouri, where infections have recently doubled and just 40% of the public is vaccinated. So he masks up in public, indoor places.

More:Why are fully vaccinated people testing positive for COVID? Should I start wearing a mask again?

While the CDC said mask-wearing isn't mandatory except in medical and transportation settings, numerous experts told USA TODAY it's a good idea to wear a mask in indoor settings with people who are possibly unvaccinated.

Wearing a mask on top of being vaccinated is the safest way to avoid getting infected or passing on the virus to someone whose weakened immune system prevented them from getting full protection from the vaccine. 

"Everyone should closely look at the environment where they are," Ellebedy said. "Delta unfortunately has brought these doubts back again."

In the United States, infections have more than doubled since the week of June 22. Total cases have risen in all 50 states since last week, and deaths also are beginning to climb, although the infection rates remain 90% below what they were at the peak in January.

That puts vaccinated people at risk because there's simply more virus out there, said Dr. George Rutherford, an infectious disease specialist at the University of California, San Francisco. 

"The more people who are running around infectious, the more you, as someone who's been vaccinated, are likely to come into contact with it," he said.

A man places flags at the National World War I Museum and Memorial Tuesday, Jan. 19, 2021, in Kansas City, Mo. The 1,665 flags represent the area residents who died in the coronavirus pandemic and the display was part of a national memorial to lives lost to COVID-19.

Unvaccinated are getting sick 

At Staten Island University Hospital in New York, there are 15 COVID-19 patients, 13 of whom are unvaccinated, said Dr. Theodore Strange, the hospital's chairman of medicine. 

One of the vaccinated patients, a 93-year-old man with many other health problems, received his shots at the beginning of the year but may have had a weaker response because of his age and health, Strange said. The remaining vaccinated patient was hospitalized for something else and didn’t know they had COVID-19 until a coronavirus test came back positive. 

Strange said his COVID-19 patients are about 10 years younger now than they were a year ago, with an average age of 55-60. Some are even younger, he said, rattling off ages: "29, 38, 42, 50."

Vaccinations deserve the credit, he said, because about 70% of people on Staten Island over 65 are vaccinated, compared with 38% of those 40 and younger.

He’s disappointed more people haven’t been willing to be vaccinated, despite the risk of infection and of “being the bullet in the gun,” potentially bringing the virus home to older, more vulnerable relatives.

He related a conversation he had last week with a patient who didn’t want to be vaccinated. Strange had recently prescribed the man a medication with many more potential side effects than the vaccines.

“The pill I gave him was clearly more much poisonous than any vaccine,” Strange said, but the man didn’t want to take something he perceived as coming from the government.

Strange has been trying an individual approach to persuade people to get the shots, including visiting a local bowling alley, churches, park benches, “whatever it takes."

But still, he said, the curve of coronavirus infections is very similar to the one followed by the 1918 flu, a pandemic that lasted three years.

“If we’re not going to avail ourselves of current technology and science," he said, "then shame on us."

Contributing: Mike Stucka

Contact Elizabeth Weise at eweise@usatoday.com and Karen Weintraub at kweintraub@usatoday.com.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.