Fact-check: Can vaccinated people spread COVID-19?

President Joe Biden: People vaccinated for COVID-19 “do not spread the disease to anyone else."

PolitiFact's ruling: Mostly False

Here's why: As President Joe Biden heads toward his second year in office of leading the country through a pandemic, he faces the challenge of trying to convince millions of unvaccinated Americans to get the COVID-19 vaccine.

The Republican National Committee said Biden has misled Americans about the effectiveness of the vaccine. The RNC tweeted a partial clip of an interview Biden gave to a Dayton, Ohio, TV station that aired Dec. 14.

"This is a pandemic of the unvaccinated," Biden said in the full interview. "The unvaccinated. Not the vaccinated, the unvaccinated. That’s the problem. Everybody talks about freedom and not to have a shot or have a test. Well guess what? How about patriotism? How about making sure that you’re vaccinated, so you do not spread the disease to anyone else."

We fact-checked a similar statement by Biden in October when he said people who are vaccinated for the coronavirus "cannot spread it to you." We found at the time that studies showed a vaccinated person was less likely to spread the virus, but the risk wasn’t zero. We rated Biden’s statement Half True. That was before the omicron variant was named a variant of concern by the World Health Organization.

At the time, Tara C. Smith, a Kent State University epidemiologist, told us: "Vaccination does significantly reduce transmission from vaccinated breakthrough cases but does not completely eliminate it."

A reader flagged Biden’s more recent remarks and asked us to look at his statement. Now that omicron has spread rapidly across the U.S. in December, we wanted to revisit the question: Can vaccinated people spread COVID-19?

We reached out again to experts to see if their understanding has changed about the role the vaccinated play in COVID-19’s transmission. We found that there is not enough data on how many people caught COVID-19 from an unvaccinated person vs. a vaccinated person in recent weeks, but scientists in general said that vaccinated people can also spread COVID-19.

Bill Hanage, associate professor of epidemiology at Harvard, said Biden’s December "statement is not accurate."

"We knew that vaccinated people could become infected with delta and shed viable virus in large amounts," Hanage said. "While data are emerging and not yet complete for omicron, this appears to be even more the case for that variant."

Biden’s emphasis on promoting vaccination is rooted in evidence that it helps protect people from serious cases, including hospitalization and death. However, we found that Biden again inaccurately characterized the vaccine when he suggested that a vaccinated individual can’t spread the virus. Any concerns experts had about the accuracy of Biden’s statement before omicron seemed to have been strengthened in the face of this new variant.

We emailed spokespersons for the White House to ask for Biden’s evidence and did not hear back.

Vaccination doesn’t eliminate risk of transmission

Some early evidence out of South Africa provided hope that the omicron variant may cause a more mild disease than earlier variants, but many patients there were younger, making them less likely to develop severe illness to begin with. Dr. Anthony Fauci, chief medical adviser to the president, told reporters Dec. 17 that the seriousness of infection is "still up in the air right now because there are a lot of confounding issues as to whether or not it is less severe."

Heather Scobie, an epidemiologist at the CDC, wrote in a Dec. 16 presentation that it’s not yet known how easily omicron spreads compared with delta. However, it is "likely that vaccinated people with breakthrough infection or people infected without symptoms can spread the virus to others." That statement was similar to one the CDC made in August.

A page on the CDC’s website updated Dec. 20 said that the "CDC expects that anyone with omicron infection can spread the virus to others, even if they are vaccinated or don’t have symptoms."

We read recent statements by Biden administration officials promoting vaccination, and none went as far as Biden to suggest that vaccination completely eliminated the chance of transmission. CDC Director Dr. Rochelle Walensky told reporters Dec. 17 that even vaccinated individuals should take precautions to reduce the spread.

John P. Moore, a professor of microbiology and immunology at Weill Cornell Medicine, said while we lack data on omicron vaccine breakthrough infections, with delta there's evidence that vaccinated people can spread infections to other people.

"That’s true on an anecdotal level (we all know such cases) and there are a few papers, mostly out of the U.K., on this point," Moore said. However, infection spread is less likely when the infected person is vaccinated, he added.

"So, the vaccines work, but they are not perfect… I would expect that to be true also for omicron," Moore said. Biden would have been on firmer ground, Moore said, if he had said "make sure you’re vaccinated, so you’re less likely to spread the disease to anyone else."

Vaccinated people are less infectious, better protected

Biden is correct that COVID-19 is primarily a disease of the unvaccinated when we look at hospitalizations and deaths, said Dr. Paul Offit, director of the Vaccine Education Center and an attending physician in the Division of Infectious Diseases at Children's Hospital of Philadelphia.

However "vaccinated people can shed virus and be contagious but generally shed virus in lower quantities and for a shorter amount of time." Offit pointed to a study from Singapore which found that vaccinated individuals who caught COVID-19 "had a more rapid decline in viral load, which has implications on secondary transmission and public health policy." The study was done based on cases earlier this year before omicron emerged.

Brooke Nichols, a health economist and infectious disease mathematical modeler at Boston University, said "vaccinated individuals can definitely infect other people. There is enough data to support this."

"While vaccinated individuals may be less infectious and infectious for a shorter duration of time they are by no means a dead-end host," Nichols said. "When calling it a pandemic of the unvaccinated, though, it makes it sound as those vaccinated individuals aren’t substantially contributing to new cases — which they are (particularly now). Unvaccinated individuals do, however, continue to contribute disproportionately to hospitalizations and deaths."

However, Nichols added, "I don’t think the data systems in place can tell us anything about the proportion of new infections that originated from a vaccinated or unvaccinated person."

We asked professors if we can draw conclusions from Cornell University, a campus that is having an outbreak even though 99% of the students are vaccinated. Is that a sign that vaccinated people are spreading the virus?

"Your statement is a reasonable inference from what’s happened on campus," Moore said, pointing to an article from the student newspaper about the spike of cases in December. "I’m not saying that’s not happening, only that I’ve not yet seen formal studies on this topic — too soon."

Our ruling

Biden said Dec. 14 that people vaccinated for COVID-19 "do not spread the disease to anyone else."

White House officials did not respond to our email asking for evidence, but Biden’s statement conflicts with information by the CDC that it is "likely that vaccinated people with breakthrough infection or people infected without symptoms can spread the virus to others." While the information from the CDC presentation was a couple of days after Biden spoke, it echoes what the CDC said in August about the potential for vaccinated people to transmit the virus.

Experts told us that getting vaccinated protects individuals from severe cases including hospitalization and death and reduces the chance of transmission, but Biden went too far when he suggested that vaccination completely eliminates the chance of transmission.

We rate this statement Mostly False.

Sources

• RNC Research, Tweet. Dec. 16, 2021

• WHIO TV, FULL INTERVIEW: News Center 7 talks one-on-one exclusively with President Joe Biden, Dec. 19, 2021

• White House, Press Briefing by White House COVID-⁠19 Response Team and Public Health Officials, Dec. 17, 2021

• U.S. Centers for Disease Control and Prevention, ​​Update on omicron variant, Dec. 16, 2021

• U.S. Centers for Disease Control and Prevention, Omicron Variant: What You Need to Know, Dec. 20, 2021

• MedRxiv, Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine-breakthrough infections: a multi-center cohort study, July 28, 2021

• CNN, Cornell University reports more than 900 Covid-19 cases this week. Many are Omicron variant cases in fully vaccinated students, Dec. 16, 2021

• Cornell University, COVID-19 Update: Moving to alert level red, changes to exams, Dec. 14, 2021

• PolitiFact, Joe Biden overstates how well vaccines prevent person-to-person virus spread, Oct. 14, 2021

• Email interview, Rebecca Valli, Cornell University spokesperson, Dec. 21, 2021

• Email interview, John P. Moore, a professor of microbiology and immunology at Weill Cornell Medicine, Dec. 21, 2021

• Email interview, Paul Offit, director of the Vaccine Education Center and an attending physician in the Division of Infectious Diseases at Children's Hospital of Philadelphia, Dec. 21, 2021

• Email interview, Bill Hanage, associate professor of epidemiology at Harvard T.H. School of Public Health, Dec. 21, 2021

• Email interview, Brooke Nichols, assistant professor of global health at Boston University, Dec. 21, 2021

This article originally appeared on Austin American-Statesman: Fact-check: Can vaccinated people spread COVID-19?