Can Vaccinated People Transmit COVID-19 to Others?

Get the answer from an infectious disease specialist
An illustration of a person getting a vaccine from a healthcare provider

We’ve heard it all since the pandemic started — lemon juice can kill the coronavirus, masks don’t work, if you already had COVID-19 you can’t get it again or that the vaccines approved for emergency use will change your DNA or put a tracking device in your body. 

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It’s almost like we need a strong dose of something to knock out all of the misinformation. But despite all the myths and urban legends, more than 60% of the U.S. population is fully vaccinated.  

Wonderful news, right? 

It should be but instead, we’ve heard myths about vaccinated people literally being magnetic or myths about them shedding vaccine components and altering the DNA of unvaccinated people. And despite the extra layer of protection, they still have to grapple with the same pandemic realities as everyone else.  

So what do vaccinated people need to do to stay safe? And is it still possible for them to spread COVID-19 to others? Infectious disease specialist Lyssette Cardona, MD, answers those questions and covers why vaccination is still one of our best weapons in the fight against COVID-19.  

“Fully vaccinated” doesn’t mean “immune to COVID-19” 

At one point, we thought that being fully vaccinated meant we could leave our masks behind and go back to the normal that we’ve been longing for. The new COVID-19 variants have pretty much killed that dream. Dr. Cardona says now is not the time to let your guard down. While the vaccines are potent, there’s still a chance that you could become infected.   

“‘Fully vaccinated’ means that you completed a COVID-19 vaccine series as recommended for the best protection against severe complications such as hospitalizations and/or death. No vaccine offers 100% protection against illness, yet it does give you a better chance to fight off the infectious consequences of being exposed to the SARS-CoV2 virus.”  

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Can fully vaccinated people still transmit the virus to others, including other vaccinated people? 

While it is possible, Dr. Cardona says that the ability to transmit COVID-19 may occur at a lower rate. She adds that this could also be a reality for people who don’t have a good immune response to vaccines.  

“The elderly, those with immune or chronic health conditions or those with underlying health disorders may not have the best protective response to vaccines, such as the COVID-19 vaccines. We are still collecting data and doing ongoing research about the vaccine responses in these vulnerable populations.” 

Why are vaccinated people still getting COVID-19? 

We’ve heard of cases where people who are in between doses or people who have received both doses are still testing positive or becoming infected with COVID-19. How is this possible? Dr. Cardona attributes this to exposure risks or where people are in the vaccination process. 

“Immunization with the COVID-19 vaccines provides the best protection within two weeks of being fully vaccinated. A person is considered fully vaccinated two weeks after receiving the second dose of Pfizer’s or Moderna’s vaccine or one dose of Johnson & Johnson’s. If someone tests positive for COVID-19 or becomes ill a few days later, they most likely were exposed before being fully vaccinated. There are reported cases of illness and/or exposure after the vaccines, but the complications of the disease for those not vaccinated yet has been of greater magnitude.” 

How long do the COVID-19 vaccines last in our bodies? 

The jury is still out on that one. According to Dr. Cardona and the Centers for Disease Control and Prevention (CDC), the exact timeframe for protection is unknown at this time. When you think about it, we all tolerate vaccines differently. So, the scientific community is still studying natural immunity and vaccine-induced immunity concerning COVID-19. 

“We don’t know exactly how long the vaccines will protect us after being fully vaccinated. However, the CDC and experts are still working to determine the answer to this question and will keep us informed of any changes. But the one thing we do know is that getting vaccinated is still the safer choice for preventing serious illness for you, your loved ones and the benefit of our communities.” 

How well are the COVID-19 vaccines protecting people? 

On June 7, the CDC issued a press release regarding their study of the effectiveness of vaccines in fully vaccinated people. The study found that the mRNA COVID-19 vaccines authorized by the Food and Drug Administration (FDA) ( Pfizer-BioNTech’s and Moderna’s) reduced the risk of infection by 91% for fully vaccinated people and 81% for partially vaccinated people. The study also is among the first to show that mRNA vaccination benefits people who get COVID-19 despite being fully vaccinated (14 or more days after dose two) or partially vaccinated (14 or more days after dose one to 13 days after dose two). 

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The results of this study also suggest that fully or partially vaccinated people who become infected with COVID-19 might be less likely to spread the virus to others. With fully or partially vaccinated study participants, the virus was 40% less detectable in their noses. It was also detected in six fewer days (i.e., viral shedding) as compared to those who weren’t vaccinated when they became infected.

In addition, people who were partially or fully vaccinated were 66% less likely to test positive for the SARS-CoV-2 infection for more than one week in comparison to those who were unvaccinated. The CDC adds that while these indicators are not a direct measure of a person’s ability to spread the virus, they have been associated with a reduced spread of other viruses like varicella (chickenpox) and influenza (flu).

What about the breakthrough cases of COVID-19?

Reports of breakthrough cases of COVID-19 among the fully vaccinated have many people doubting the vaccines’ effectiveness. However, the CDC says that these breakthrough cases are not an indication that the vaccines don’t work. So far, breakthrough infections have occurred among a small amount of fully vaccinated people, even with the delta variant. These infections have been mild so far as compared to those who were unvaccinated. While there have been some outliers, the CDC reports that fully vaccinated people are much less likely to be hospitalized or die than people with similar risk factors who are not vaccinated. Because this is a constantly evolving situation, they are working with state and local health departments to investigate breakthrough cases of COVID-19.

It’s still good to be cautious 

While this is encouraging news, Dr. Cardona stresses that fully vaccinated people still need to be careful as everything opens up again.  

“Virus transmission may still occur from those who are infected and asymptomatic, or ill without knowing it, especially in crowded areas with a lack of physical distancing, respiratory precautions and hand washing. Other factors to consider are ongoing community transmission (positivity of testing) and immunization rates.”  

If you haven’t been vaccinated or haven’t completed the vaccination series, she recommends doing so. And if you have a unique circumstance that delays your ability to complete your series of shots as scheduled, still get the second dose. Dr. Cardona says restarting the series isn’t necessary. 

The CDC also recommends that fully vaccinated people wear masks indoors in public for maximum protection from the delta variant and to lessen the risks of transmission. You should also wear a mask if you have a weakened immune system, an underlying medical condition or are at high risk for severe disease.

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