The highly transmissible omicron variant is likely increasing the number of breakthrough infections among the vaccinated as it continues to surge across the United States. And while research suggests these breakthrough infections can significantly increase immunity against future coronavirus infections, many health experts still encourage pandemic precautions post-breakthrough.
How many people have experienced breakthrough infections?
According to data from Johns Hopkins University, at least 20% of Americans—or over 66 million people—have had Covid-19 since the beginning of the pandemic. Of this number, a small portion has been breakthrough cases among those who are vaccinated.
Although it is difficult to quantify the exact number of breakthrough cases that have occurred—largely due to lack of comprehensive tracking—a CDC analysis of 27 states found that 1.8 million breakthrough infections occurred between April and November 2021. Around 96% of these infections occurred after June when the delta variant began spreading in the United States.
Breakthrough infections among the vaccinated were seemingly rare occurrences. According to an ABC News analysis of 36 states, only around 1.37% of those who were fully vaccinated developed a breakthrough infection between January and December 2021. Hospitalizations and deaths from breakthrough infections were similarly low during the same time period at around 0.05% and 0.01%, respectively.
However, since the highly transmissible omicron variant emerged, experts have warned that breakthrough infections are likely to become more common.
"With omicron displaying increased transmissibility, breakthrough cases will unfortunately become even more normalized," said John Brownstein, and epidemiologist at Boston Children's Hospital.
Breakthrough infections boost immunity, but experts still urge caution
Several studies suggest that a combination of vaccine immunity and natural infection can result in a "hybrid immunity" that significantly boosts a person's immune system against the coronavirus. For example, a recent study of vaccinated health care workers who had developed breakthrough infections found they had significantly higher antibody levels compared to a control group that had only been vaccinated.
However, this doesn't mean that people who have had breakthrough infections can simply stop practicing safety precautions. According to several health experts, the level of protection provided by hybrid immunity can vary from person to person and may wane over time.
"Going back to 2019 behavior is a little premature," said Akiko Iwasaki, an immunologist at Yale University. "It's really just playing the lottery, because you don't know how many antibodies you've generated."
Separately, Shane Crotty, a virologist at the La Jolla Institute of Immunology said that, while hybrid immunity is "the best immunity you can get," it's not "a force field that can completely stop [infection from the coronavirus] no matter what."
Health experts have also warned against trying to get infected on purpose to develop hybrid immunity as the coronavirus is unpredictable and can result in severe illness even in young people.
"I really worry that people will intentionally get infected so they can get to this 'new normal,'" said Celine Gounder, an infectious disease specialist at Bellevue Hospital Center. "Something could go wrong, and they could end up in the hospital."
In addition, even with hybrid immunity, people still are at risk of being reinfected and potentially spreading the virus to others, including those who are more vulnerable to severe disease from Covid-19. According to Jennifer Gommerman, an immunologist at the University of Toronto, some vaccinated people who were previously infected with delta have been reinfected with omicron.
"You have to remember there are vulnerable people in the community, and we have to continue to do things like wearing masks," Gounder said. "It's not just about protecting yourself, it's about protecting other people."
However, what recovering from a breakthrough infection can bring to vaccinated people, especially those who are young and otherwise healthy, is "some peace of mind," the New York Times writes, allowing them to live their lives with less fear and worry.
According to Ashish Jha, dean of the Brown University School of Public Health, people who have had breakthrough infections, particularly if they have also been boosted and are not at high risk of severe disease, should feel confident about their level of protection for at least the first three months following the infection.
"Could you get reinfected? Yeah, if somebody in their most contagious moment hacks in your face over and over, maybe," Jha said, but "a normal interaction in a restaurant or a bar" is likely safe. (Mitropoulos, ABC News, 12/21/21; Langmaid, CNN, 1/18; Blum, New York Times, 1/19)