Fact check: Study on breakthrough delta cases in Vietnam misrepresented online

CLAIM: A preprint paper by the prestigious Oxford University Clinical Research Group, published Aug. 10 in The Lancet, found vaccinated individuals carry 251 times the load of COVID-19 viruses in their nostrils compared to the unvaccinated.

AP’S ASSESSMENT: False. The study is being misrepresented. It found vaccinated health care workers with breakthrough infections caused by the coronavirus delta variant had higher viral loads — the amount of virus detected in a person — compared to patients infected with earlier strains of the virus. Furthermore, other studies that compare the viral loads between vaccinated and unvaccinated delta patients found similar amounts of viral material in the two groups.

THE FACTS: The website, The Defender, which is published by the anti-vaccine organization, Children’s Health Defense, posted an article this week that distorts the findings of a recent study of breakthrough delta infections among vaccinated hospital staff in Vietnam.

The misleading article, written by Dr. Peter A. McCullough and posted online on Aug. 23, claims the study found vaccinated individuals carry “251 times the load of COVID-19 viruses in their nostrils compared to the unvaccinated,” and pose a “threat to unvaccinated patients, co-workers.” The article falsely blames the delta-driven surge in new COVID-19 cases on vaccinated people who are “acting as powerful Typhoid Mary-style super-spreaders of the infection.”

Robert F. Kennedy Jr., who is the founder and chairman of the board of Children’s Health Defense and has a history of posting vaccine misinformation, tweeted the article in a post that was shared 3,000 times.

But the article, and associated social media posts, distort the study’s findings, according to the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam, which conducted the study in partnership with the Hospital for Tropical Diseases.

“It’s unfortunate that our study was completely misinterpreted and misquoted by an anti-vaxx website,” Chi Ngo, senior communications officer for the research unit, told The Associated Press in an email.


Ngo said the research unit does not support “any statement” shared in McCullough’s article and is working to report social media posts sharing the false information.

The study, shared online by The Lancet as a preprint for research purposes, has not yet undergone peer review needed by a scientific journal. It did not compare vaccinated peopleinfected with the delta variant to their unvaccinated counterparts. Rather, it compared the viral loads of vaccinated hospital workers — who had been infected with the highly contagious delta variant — to viral load data from early in the pandemic.

The health care workers in the study had previously received the AstraZeneca vaccine but were infected with breakthrough cases in June.

“Viral loads of breakthrough Delta variant infection cases were 251 times higher than those of cases infected with old strains detected between March-April 2020,” the preprint paper reads.

While it is true that vaccines were not available at that time, the study was designed to compare how different strains of coronavirus impacted viral load, not vaccination status.

Lead authors of the study, Dr. Nguyen Van Vinh Chau, Dr. Guy Thwaites and Dr. Le Van Tan, released a statement late Friday to clarify this point further.

“The differences in viral load were driven by the ability of the Delta variant to cause higher viral loads; they had nothing to do with the vaccination status of the infected individual,” the authors wrote. “Thus the claim that vaccinated individuals carry 251 times the loads of SARS-CoV-2 in their respiratory tract compared to the unvaccinated people is a misrepresentation of the data.”

According to Ngo, the study shows that the delta variant is more transmissible and dangerous compared to earlier strains of the virus, and therefore safety measures like mask-wearing, hand-washing and social distancing are still advised even among vaccinated people.

“We strongly endorse vaccination as a critical tool against COVID-19 and the terrible consequences of the pandemic,” wrote the authors in their statement, noting that that their study does not undermine the “overwhelming evidence” that vaccines are effective at preventing severe disease and death due to COVID-19.

The authors also pointed to other recent studies that compare delta infections in vaccinated and unvaccinated people have found the two groups have similar viral loads — not that vaccinated people carry more virus.

Dave O’Connor, a professor of pathology and laboratory medicine at the University of Wisconsin School of Medicine and Public Health who has researched the topic, agreed.

“The existing data, from multiple studies, in multiple continents, is that the amount of delta genetic material measured in the nose is similar between those who are unvaccinated and those who are infected despite vaccination,” O’Connor said.

And contrary to the false claim in McCullough’s article, experts say there is evidence that vaccinated people infected with the delta variant are less likely to infect others compared to unvaccinated people.

Jennifer Nuzzo, a senior scholar at Johns Hopkins University’s Center for Health Security, said those who are vaccinated and catch the delta variant of the virus can clear the infection faster than unvaccinated patients.

“This helps lessen the chances that vaccinated people who get infected will have severe illness, but also makes them less likely to transmit their infections to others as compared to unvaccinated cases,” Nuzzo said.

Kennedy told the AP on Friday that his organization had reviewed McCullough’s article in light of the comments by Oxford University Clinical Research Unit. “We are confident that everything in our article is accurate,” Kennedy said. “However, we will also add links to recent articles that show equivalent viral loads in vaccinated and unvaccinated cohorts.”

Early Saturday a clarification note appeared below McCullough’s article acknowledging that the study compared two different variants of coronavirus, and “differences between these two groups aren’t a result of vaccination status alone.” The note also included links to two studies that found comparable viral loads between vaccinated and unvaccinated delta patients.

McCullough did not respond to a request for comment.