COVID-19 vaccines are incredibly effective at preventing infection, but like other shots to protect from other diseases, the defense is not 100% impenetrable.
When a person has been fully vaccinated for COVID-19, but still tests positive for the new coronavirus, the case is known as a breakthrough infection.
Out of more than 86 million Americans who have been fully vaccinated, there have been 5,814 reports of such cases from 43 U.S. states and territories as of April 13, according to the Centers for Disease Control and Prevention.
“That’s such a small number. It’s an important number, but it’s a very, very small number,” Dr. Georges Benjamin, executive director of the American Public Health Association, told TODAY.
“No vaccine is 100% protective against COVID, but (breakthrough infections) are very rare.”
Benjamin, who is also an infectious disease expert and former secretary of the Maryland Department of Health and Mental Hygiene, weighed in on what people should know:
What is a breakthrough case?
A small percentage of people who are fully vaccinated — those who are at least two weeks after their final dose of a coronavirus vaccine — will still get sick, be hospitalized or die from COVID-19, the CDC cautioned.
Breakthrough cases are expected and they happen with other shots as well, Benjamin said.
“This is not unusual, so people should not think that the vaccine is doing something different than other vaccines. No vaccine is 100%,” he noted.
The symptoms might be less severe if a person gets COVID-19 after vaccination and the overall risk of hospitalization and death will be much lower than for people with similar risk factors who aren’t vaccinated, according to the CDC.
Why do breakthrough infections happen?
“The vaccine teaches your body how to produce an immune response to destroy the virus. And like everything else in biology, there’s a huge variance in how effective that can be,” Benjamin said.
COVID-19 variants may play a role in some cases, but the original strain may also get past defenses created by the vaccine.
It remains to be seen whether certain populations — such as the elderly or people taking medications that suppress their immune systems — are at higher risk for having a breakthrough infection. “That’s a hypothesis that needs to be proven, but there’s a high likelihood,” Benjamin noted.
Current CDC data shows breakthrough infections were reported among people of all ages, though almost two-thirds were women.
About a third of people with breakthrough infections didn’t have symptoms, 7% were hospitalized and 1% died.
How are these cases reported and tracked?
A case of someone who’s been fully vaccinated and still tests positive for COVID-19 would be reported to the person’s state and local health department, which then report it to the CDC, Benjamin said.
“This is something that we take seriously and follow closely,” Dr. Anthony Fauci said during a White House news conference last month.
The CDC then examines each patient’s demographics, location, time since vaccination, vaccine type or lot number and coronavirus strain. The agency has been monitoring all reported vaccine breakthrough cases, but soon plans to focus on only those that lead to hospitalization or death since these are “of greatest clinical and public health importance,” officials noted.
A breakthrough infection has to be picked up first. Since it’s possible some fully-vaccinated people might have COVID-19 but show no symptoms, the cases may be under-reported. But “if they get picked up, they get well tracked,” Benjamin noted.
Why is it important to track breakthrough infections?
“It’s very important to track them because that tells you a lot about the efficacy of your vaccine over time,” Benjamin said.
A sudden cluster of cases may indicate the vaccine those patients received is no longer protective. Any changes in the baseline will allow health officials to decide whether or not a booster shot or a new vaccine series are needed.
What should people make of the current number of breakthrough infections?
Experts say the data so far is reassuring: 5,814 cases out of 86 million people fully vaccinated amounts to a rate of about 0.0067%, which Benjamin called almost a rounding error.
“You will see breakthrough infections in any vaccination when you’re vaccinating literally tens and tens and tens of millions of people. So, in some respects, that’s not surprising,” Fauci said.
"This is a really good scenario, even with almost 6,000 breakthrough infections," Tara Smith, a professor of epidemiology at the Kent State University College of Public Health in Ohio, told NBC News.
But if health officials saw a steep growth in these numbers, that would be a concerning trend, Benjamin noted
Yes, you can still get COVID-19 after being fully vaccinated, though it’s very rare.
It’s one of the reasons why the public health guidance today still advises people who’ve had all of their shots to keep taking precautions like wearing a mask, socially distancing and avoiding crowds and poorly ventilated spaces.