This Is How Common Breakthrough Infections Really Are, New Data Says

Preliminary data has found the fully vaccinated may be getting sick more often than originally thought.

What was once expected to be the summer that saw the end of the COVID-19 pandemic has become the season of its resurgence. The arrival of the highly transmissible Delta variant has caused new cases to spike once again, especially among those who are unvaccinated. But the now-dominant strain poses another threat in that it has also been known to occasionally infect those who are fully vaccinated. Now, early data has found that breakthrough infections are more common than we originally thought—as are resulting hospitalizations and deaths, The New York Times reports.

RELATED: If You Got Pfizer, This Is When You're More Likely to Get Breakthrough COVID.

To better understand the rates of infection in fully vaccinated people, The Times collected data from seven states—California, Colorado, Massachusetts, Oregon, Utah, Vermont, and Virginia—selected for keeping particularly detailed records. Analysis showed that in six of the states, breakthrough infections made up 18 to 28 percent of all newly diagnosed cases of COVID-19 in the past several weeks. Results also found that fully vaccinated people made up 12 to 24 percent of all COVID-related hospitalizations, and while the number of deaths was too small to be considered significant, it is likely higher than the original Centers for Disease Control and Prevention (CDC) estimates of .5 percent.

The figures on non-hospitalized breakthrough infections are also assumed to be underestimations since many fully vaccinated people who become infected may not feel sick enough to be tested for the virus, The Times reports. Official data has also been scarce since the CDC stopped recording cases that didn't lead to hospitalization or death in May. But the recent analysis shows a stark change from previous estimates that calculated there were about 35,000 symptomatic breakthrough infections per week among 162 million vaccinated Americans, according to an internal presentation from the agency obtained by The Washington Post.

While the data may change the overall outlook on breakthrough infections, absolute numbers still support the conclusion that available vaccines remain highly effective, The Times reports. But the findings could inform fully vaccinated people when it comes to going about their daily lives amid the surge of the Delta variant.

"Remember when the early vaccine studies came out, it was like nobody gets hospitalized, nobody dies," Robert Wachter, MD, chairman of the department of medicine at the University of California, San Francisco, told The Times. "That clearly is not true."

RELATED: If You Got This Vaccine, Your Risk of COVID After Vaccination May Be Higher.

Other recent research has shed light on how common breakthrough infections may be. One large study conducted by researchers at Imperial College London used data from over 98,000 swab tests taken between June 24 and July 12, covering a time when the Delta variant had surpassed the Alpha variant as the dominant strain in the U.K. Results found that people who had received two doses of vaccine were half as likely to test positive for COVID-19 even if they hadn't shown any signs of symptoms. It also found that the vaccines offered even higher effectiveness regarding symptomatic infections, showing a 59 percent efficacy rate for those who had received both shots.

The findings suggested a significant drop from a previous study conducted by Public Health England that found fully vaccinated people were offered 88 percent protection against the variant. But the Imperial College researchers stated that the point of their study was to assess results from people who may not have been looking to get tested, saying they were "looking at effectiveness against infection amongst a random sample of the general population, which includes asymptomatic individuals," Reuters reports.

Still, as outbreaks continue, one medical expert claimed there was a straightforward explanation for the rise of breakthrough infections. "Part of it is simple math: We can and should expect that as the overall number of cases goes up, the number of breakthroughs is going to go up," David Dowdy, MD, an infectious diseases physician at Johns Hopkins, told The Wall Street Journal. He also pointed out that our attitudes towards risk and safety measures are changing, adding: "We are all interacting with one another more closely than we were a few months ago."

RELATED: For more up-to-date information, sign up for our daily newsletter.

And while the new data may offer a slightly more dire picture of what's happening with the pandemic, one expert cautioned that the findings also held some good news. "We don't want to dilute the message that the vaccine is tremendously successful and protective, more so than we ever hoped initially," Scott Dryden-Peterson, MD, an infectious disease physician and epidemiologist at Brigham & Women's Hospital in Boston, told The Times. "The fact that we're seeing breakthrough cases and breakthrough hospitalizations and deaths doesn't diminish that it still saves many people's lives."

RELATED: If You're Vaccinated, Your COVID Symptoms Could Be Different, Study Says.

Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
Filed Under