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Fact Check: Are Vaccinated People Just As Likely To Spread COVID-19 As Unvaccinated People?


Dr. Katie Spalding


Dr. Katie Spalding

Freelance Writer

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

infected person in crowd

Vaccination reduces your chances of spreading COVID-19 for one pretty glaring reason. Image Credit: Lightspring/Shutterstock

The COVID-19 pandemic may have claimed nearly five million lives so far, but there’s one group of people for which it’s been a real boon: conspiracy theorists. Does the vaccine cause miscarriages? (No.) Can’t I take ivermectin instead? (No, and you’d better prepare yourself for some seriously unappealing side effects.) And of course, everybody’s favorite: what about that rapper’s cousin’s friend’s gigantic balls?

Another one you may have heard is the idea that vaccinated people are “just as likely” to spread the virus as unvaccinated people. Sometimes this is said out of an overabundance of caution – as in, “the reason I haven’t left my house in three months despite being fully vaccinated is because vaccinated people are just as likely to spread the virus as unvaccinated people” – and sometimes it’s said to justify a complete lack of it – you know, “why should I bother getting vaccinated when vaccinated people are just as likely to spread the virus as unvaccinated people?” But either way, it’s a misunderstanding of the facts – so let’s take a look at what’s really going on.


“Let me make one thing clear: Vaccinated people are not as likely to spread the coronavirus as the unvaccinated,” writes Craig Spencer, an emergency-medicine physician and director of global health in emergency medicine at New York Presbyterian/Columbia University Medical Center, in The Atlantic last week.

“Even in the United States, where more than half of the population is fully vaccinated, the unvaccinated are responsible for the overwhelming majority of transmission.”

It’s not hard to see where the confusion has come from: the last six months or so has been a whirlwind of conflicting headlines, after all. First, we had the director of the CDC Rochelle Walensky saying on national TV that “vaccinated people do not carry the virus.” Then, the scientific community almost immediately pushed back, with a CDC spokesperson pointing out to the New York Times that “the evidence isn’t clear whether they can spread the virus to others", and there’s really no vaccine in the world that has 100 percent effectiveness like that.

Pair that with the news that COVID-19 cases are rising among the double-vaccinated – in some hospitals, unvaccinated cases are even becoming the minority – and it’s easy to get confused.


So what’s going on? Well, the problem here isn’t so much to do with science or statistics as it is to do with language. The statement that “vaccinated people are just as likely to spread the virus as unvaccinated people” might be true if you’re talking about vaccinated people who are infected with COVID-19, but if you’re talking about vaccinated people as a whole – both healthy and currently infected with the virus – then it’s not true at all.

“This framing [misses] the single most important factor in spreading the coronavirus: To spread the coronavirus, you have to have the coronavirus,” explains Spencer. “And vaccinated people are far less likely to have the coronavirus – period.”

“Additionally, for those instances of a vaccinated person getting a breakthrough case, yes, they can be as infectious as an unvaccinated person,” he added. “But they are likely contagious for a shorter period of time when compared with the unvaccinated, and they may harbor less infectious virus overall.”

Spencer likened the effect of vaccination on the spread of COVID-19 to a rampage through a city: in unvaccinated populations, he said, “the virus travels unhindered on a highway with multiple off-ramps and refueling stations. In the vaccinated, it gets lost in a maze of dead-end streets and cul-de-sacs.”


“Every so often, it pieces together an escape route, but in most scenarios, it finds itself cut off, and its journey ends,” he explained. “It can go no further.”

To put it another way: when 30 people met at a party back in July and spread the Delta variant around, it was the six vaccinated guests who managed to avoid infection. The other 24 guests, therefore, were definitely more likely to spread the virus, purely because they got it and the vaccinated group didn’t – and you can’t spread an illness you don’t have.

“Despite concern about waning immunity, vaccines provide the best protection against infection,” wrote Spencer. “And if someone isn’t infected, they can’t spread the coronavirus. It’s truly that simple”



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