Breakthrough infections — fully vaccinated people testing positive for COVID-19 — seem to be cropping up everywhere, from the Tokyo Olympic Games to the White House and Congress.
And public health officials say such infections may be contributing to the spread of the coronavirus, although unvaccinated people account for most of the recent surge of COVID-19 cases. They point to the virulence of the coronavirus’s delta variant, which first emerged in India.
“What we have learned with the delta variant, which is so highly contagious with an awful lot of spread among the unvaccinated, there’s been spillover into people who are vaccinated and we’re seeing more so-called breakthrough infections,” said Dr. William Schaffner, an infectious disease professor at Vanderbilt University.
“One of the things we’ve learned is that, although people shed less virus when they are vaccinated, some of those vaccinated people can be transmitters — and that has become more apparent with the delta strain,” he said.
Dr. Schaffner said that people infected with the delta variant have more viral load and exhale much more of the virus, although estimates of the strain’s transmissibility vary. At worst, the delta variant could produce 1,000 times more virus in the throat, he said, citing a Chinese study.
In a COVID-19 update Wednesday, Maryland Gov. Larry Hogan cited recent data that the delta variant is 225% more transmissible than the original coronavirus strain, putting the unvaccinated particularly at risk.
Although the majority of transmission is coming from the unvaccinated, there are “rare occasions” where vaccinated people infected with the delta variant might be spreading the virus to others, Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said this week.
The CDC on Tuesday revised its mask guidance, recommending vaccinated Americans wear face coverings in schools and public indoor spaces in areas with high transmission of the coronavirus, partially due to data showing that fully inoculated people may be able to spread the virus.
Six Texas Democratic lawmakers who fled to Washington, D.C., to halt passage of an election bill have tested positive for the coronavirus, although they were vaccinated.
Breakthrough infections also have been reported in a White House official and an aide to House Speaker Nancy Pelosi along with several congressional staff members.
Before the Olympics started, U.S. gymnast Kara Eaker tested positive for COVID-19 at a training camp outside Tokyo even though she said she was vaccinated, The Associated Press reported. WNBA player Katie Lou Samuelson also tested positive despite being inoculated, She withdrew from the Olympics’ 3-on-3 basketball competition.
As of July 19, 5,914 patients with COVID-19 vaccine breakthrough infections who were hospitalized or died have been reported to the CDC. By that date, more than 161 million people in the U.S. were fully vaccinated.
Of those breakthrough infections, 74% or 4,392 patients were people 65 years and older. Twenty percent of these patients, or 1,164, experienced asymptomatic infections. The CDC reported 1,141 deaths among those with severe vaccine breakthrough cases, but 26% of these cases were reported as asymptomatic or not related to COVID-19.
It is probable that the number of COVID-19 vaccine breakthrough cases is higher than what’s been reported to the CDC, the agency says, but the infections affect only a small percentage of inoculated people. While coronavirus vaccines are effective, they do not 100% prevent illness in vaccinated people, the CDC notes.
According to Mr. Hogan, only 0.07% of Maryland’s entire vaccinated population has had a COVID-19 breakthrough infection, demonstrating a 99.93% vaccine effectiveness.
“Breakthrough infections occur because the vaccine is not a big zapper or forcefield. Tiny bits of viral genetic material being found in the nose is usually not clinically significant, rare, and not evidence of the vaccine failing,” said Dr. Amesh Adalja, senior scholar for Johns Hopkins Center for Health Security.
“On the contrary, it is evidence of the vaccine working as it is severely blunting the impact of infection. Breakthrough disease is exceedingly rare and hospitalization even rarer,” Dr. Adalja said. “The primary aim of the vaccines is to prevent serious disease, hospitalization and death — they do that tremendously.”
Compared to someone who isn’t vaccinated, those with breakthrough infections could experience no symptoms or extremely mild ones, experts say.
Dr. Schaffner said these infections often sound like a “bad cold” for people who are vaccinated. He said some research and anecdotal evidence also suggests that there might be a lower occurrence of cough and loss of taste and smell among those who are vaccinated but catch COVID-19.
He added that COVID-19 vaccines remain successful in preventing severe disease, noting that most breakthrough infections are mild and don’t require hospitalization.
Clinical evidence does not appear to point to a greater frequency of breakthrough infections with any of the vaccines available in the U.S., said Dr. Adalja. However, he noted that infections might be more common with Chinese vaccines as seen in Seychelles.
It could be that breakthrough infections are more common the longer it has been since COVID-19 vaccination, Dr. Adalja suspects. Although that is not surprising and “not a major concern” as long as people are still protected from severe disease, he added.
Breakthrough infections are more likely to occur with the delta variant, the dominant strain that is currently circulating in the U.S., since the amount of viral exposure could be higher due to its “increased fitness,” he said. The beta variant has also reportedly caused breakthrough infections.
Dr. Adalja recommends those who are immunocompromised and in a high transmission area to wear a mask even if fully vaccinated.
“For others, I think it’s about risk tolerance because breakthrough infections are not clinically significant and are not driving infections in this country,” he said. “The goal of the vaccine program was not to eliminate COVID-19, which is impossible, but to reduce its ability to cause serious disease, hospitalizations, and death; to deny the ability to threaten hospital capacity; to make it more like other respiratory viruses as we deal with year in and year out.”
If mostly seeing milder breakthrough infections among those inoculated, vaccine booster shots will not likely be necessary, Dr. Schaffner said. But if more and more vaccinated people start to require hospitalization for severe COVID-19 disease, he said booster shots might be needed in the future.