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No, Vaccinated People Are Not ‘Just as Likely’ to Spread the Coronavirus as Unvaccinated People

This has become a common refrain among the cautious—and it’s wrong.

Katie Martin / The Atlantic

For many fully vaccinated Americans, the Delta surge spoiled what should’ve been a glorious summer. Those who had cast their masks aside months ago were asked to dust them off. Many are still taking no chances. Some have even returned to all the same precautions they took before getting their shots, including avoiding the company of other fully vaccinated people.

Among this last group, a common refrain I’ve heard to justify their renewed vigilance is that “vaccinated people are just as likely to spread the coronavirus.”

This misunderstanding, born out of confusing statements from public-health authorities and misleading media headlines, is a shame. It is resulting in unnecessary fear among vaccinated people, all the while undermining the public’s understanding of the importance—and effectiveness—of getting vaccinated.

So let me make one thing clear: Vaccinated people are not as likely to spread the coronavirus as the unvaccinated. 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.

I understand why people are confused. In April, after months of public-health experts cautiously promoting the merits of vaccination, CDC Director Rochelle Walensky cited new real-world data of the shots’ effectiveness to jubilantly proclaim that “vaccinated people do not carry the virus.” The CDC later walked back her comment, but headlines such as “It’s Official: Vaccinated People Don’t Transmit COVID-19” had already given many the impression that in addition to their remarkable protection against infection with the coronavirus, the shots also prevented them from passing the illness on to others.

Scientists and researchers objected, warning that there weren’t enough data to support such a proclamation. Their concerns were prescient. As Delta first took hold early this summer and then quickly spread, our collective relief turned into dejection.

An outbreak in Provincetown, Massachusetts—in which 74 percent of the 469 cases were in the fully vaccinated—forced the CDC to update its mask guidance and issue a sad and sobering warning: Vaccinated people infected with the SARS-CoV-2 Delta variant can be just as contagious as unvaccinated people.

In the aftermath of the Provincetown announcement, many who had gotten their shots were confused about what the news meant for them, especially when headlines seemed to imply that vaccinated individuals are as likely to contract and transmit COVID-19 as the unvaccinated. But this framing missed the single most important factor in spreading the coronavirus: To spread the coronavirus, you have to have the coronavirus. And vaccinated people are far less likely to have the coronavirus—period. If this was mentioned at all, it was treated as an afterthought.

Despite concern about waning immunity, vaccines provide the best protection against infection. And if someone isn’t infected, they can’t spread the coronavirus. It’s truly that simple. Additionally, for those instances of a vaccinated person getting a breakthrough case, yes, they can be as infectious as an unvaccinated person. But they are likely contagious for a shorter period of time when compared with the unvaccinated, and they may harbor less infectious virus overall.

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That’s why getting more people their shots is crucial for controlling the spread of the coronavirus: Every vaccinated person helps limit the virus’s ability to hide, replicate, and propagate.

Among the unvaccinated, 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. It can go no further.

This is borne out by recent data from New York City that show that more than 96 percent of cases are among the unvaccinated. Only 0.33 percent of fully vaccinated New Yorkers have been diagnosed with COVID-19.

To highlight what this means in the real world, imagine two weddings with 100 guests, one where everyone is unvaccinated and another where all the guests are vaccinated.

In the unvaccinated wedding group, the likelihood that at least one of the guests has COVID-19 is high. Similarly, everyone present is more susceptible, and the virus will likely infect many others, given the increased transmissibility of the Delta variant.

At the wedding with exclusively vaccinated attendees, however, the likelihood that anyone present has COVID-19 is minuscule. Even if someone present is infected, the likelihood that the other guests will contract the virus is similarly low, given the protection afforded by their shots.

This is exactly why vaccine mandates are so important—and why going to events that exclude unvaccinated people is much, much safer than those that are open to all. Everyone knows that the vaccines help protect each individual who gets their shots. But when more people get vaccinated, this helps keep everyone else (including children and others ineligible for vaccination) safe as well.

It’s worth acknowledging that even though the vaccines are our best protection—and still do what we need them to do very well—they’re not perfect. Vaccinated individuals can experience breakthrough infections, and when they do, they can potentially infect others. Some may also develop long COVID, although thankfully the shots dramatically lower this risk too. These reasons are exactly why, in many circumstances, mitigation measures such as masking and mandates still make sense to help limit the spread, even for the vaccinated.

As an emergency-medicine physician, I’ve seen firsthand the vaccines’ dramatic role in reducing severe outcomes from a virus that flooded my emergency room early in the pandemic. And as a member of one of the first groups vaccinated in the rollout, I was kept safe by the shots while I cared for patients, and they prevented me from bringing the virus home to my family.

But ultimately, a COVID-19 diagnosis in someone close to me is what highlighted why the assertion that the vaccinated are as likely to spread the coronavirus as the unvaccinated is so wrong.

Recently my cousin contacted me when her daughter tested positive for COVID-19. Her daughter fell ill just weeks before her 12th birthday, when she would’ve been eligible for a vaccine. My fully vaccinated cousin spent nearly every moment at her side—always indoors and usually unmasked—yet never fell ill herself.

“The vaccine seems to be working. It’s magic!” she texted me. Before getting her shots, she would have almost certainly been infected, and likely passed it on to others. But the vaccine broke the chain of transmission. My cousin never spread her daughter’s COVID-19 to anyone because she never caught it.

Craig Spencer is an emergency-medicine physician and director of global health in emergency medicine at New York Presbyterian/Columbia University Medical Center.