The coronavirus vaccines have been hailed as miracles of science and technology, and rightly so. Because of widespread vaccination, the average number of new COVID-19 cases in the United States is the lowest it’s been since last fall. Hospitalizations and deaths among elderly Americans have plummeted. As Anthony Fauci, the nation’s top infectious disease expert, exhorts us all: be “really grateful that we have three really efficacious vaccines.”
Yet for all the good news surrounding COVID-19 vaccines, it can still feel difficult — and even frightening — to grapple with the fact that it’s still possible to get COVID-19 once you’re fully vaccinated. It doesn’t help that breakthrough cases have been pounced on by vaccine opponents looking to seed and spread doubt.
Are you wondering why so-called “breakthrough” cases happen, and how common they are? Here are some basics to have in mind.
Breakthrough cases are really rare.
First, a simple (but important) reminder from the Centers for Disease Control and Prevention: “No vaccine prevents illness 100% of the time.” For every vaccine, there will be breakthrough cases. The Moderna, Pfizer, and Johnson & Johnson COVID-19 vaccines are no exception, and experts have known this from the get-go.
In clinical trials before widespread vaccination, the Pfizer vaccine was 95% effective against symptomatic disease, the Moderna vaccine was 94.5% effective against symptomatic disease, and the Johnson & Johnson vaccine was 66% effective at preventing symptomatic disease (as well as 85% effective at preventing severe disease).
The CDC has been tracking breakthrough cases in real time since then, as millions of Americans have rolled up their sleeves and public health officials have been able to get a better sense of what the risk of infection post-vaccination really is. As of later April, the CDC says that among more than 95 million people in the U.S. who’d been fully vaccinated, the agency knew of roughly 9,000 breakthrough infections.
“It’s not something unexpected, and the numbers we’re seeing now are really minuscule,” Taylor Nelson, an infectious disease specialist with MU Health Care, told HuffPost. “It’s a small fraction — of a percentage — of people who are having breakthrough infections.”
Experts aren’t clear yet on how many breakthrough infections are related to the variants of concern that groups like the CDC are tracking, though the earliest evidence on how the vaccines are holding up in real-world conditions is promising.
“When we have a case that we think is a breakthrough infection, we try and send the sample off for sequencing to see: Is there a pattern? Is it this variant or that variant that’s more likely to give someone a breakthrough?” Nelson said. “But I don’t know that we have those answers yet.”
It’s looking pretty likely that breakthrough cases are less severe.
The CDC is being cautious about overselling this point, saying that “there is some evidence that vaccination may make illness less severe.”
About 27% of the breakthrough cases the CDC is aware of have been asymptomatic infections, for example. This is not to say that really serious outcomes are impossible. There have been 835 hospitalizations among those who are fully vaccinated against COVID-19 (though 30% of those were categorized as asymptomatic, or not related to COVID-19), and there have also been 132 deaths — though again, not all of those were necessarily directly related to COVID-19.
“The vaccine still elicits some immune response to help your body fight infection and that translates into a more mild infection,” Nelson said. “There’s probably a lower likelihood of transmitting, too.”
There aren’t any clear patterns about who is at risk.
The current CDC data on breakthrough cases suggests that about 60% of the reported breakthrough infections have been in women, though it’s too early to say anything about why that might be. It could be because women are more likely to seek out health care, or because women’s immune systems somehow respond differently to the vaccine than men’s.
And about 40% of breakthrough cases were in people age 60 and up, although again, that could simply be because older Americans have been vaccinated in higher numbers. All of which means that at this point, there aren’t really clear patterns about who appears to be at greater risk of breakthrough infection.
“I don’t know there is a pattern we can really identify yet,” said Nelson. “I would say something that we think about obviously are these new variants that are out there.”
It’s also worth noting that it’s not totally clear yet how long immunity lasts after vaccination, though research suggests it’s at least six months. So there might be some confusion in the future about what are true breakthrough cases versus those that pop up as people’s immunity potentially begins to wane.
“Unfortunately, only time can tell us how long these vaccines are going to be as effective as they are,” Nelson said. “I think the general thought is that probably at least about a year.” But we won’t really have a clear picture of that until next fall or winter, she added.
It’s important to stay on top of changing recommendations about post-vaccine life — and follow them.
The CDC has been slowly changing its guidance about what people can do once they’re fully vaccinated. It’s OK to gather with a small group of friends outdoors while unmasked, for example, or to go on a walk or bike ride. If you’re fully vaccinated, it’s also generally safe to travel within the U.S. Our current COVID-19 vaccines really do confer robust protection, and health experts want everyone who has been really starved for normalcy, connection and physical affection to enjoy the freedoms vaccination offers.
Remember: the fact that there have been breakthrough cases (and there will continue to be) “is not a vaccine failure by any stretch of the imagine,” Nelson said.
But there are still times when the CDC urges fully vaccinated Americans to take preventive measures like mask-wearing, maintaining social distance and hand-washing — particularly when you’re in a crowded or poorly ventilated space.
“If you’re around people who are not fully vaccinated, or you’re around someone who can’t be vaccinated ... or you’re in a crowd or an area with poor ventilation, it’s probably important to keep doing those other mitigation measures,” Nelson said.
Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.
This article originally appeared on HuffPost and has been updated.