Does the COVID vaccine prevent coronavirus transmission? A study at the University of Maryland seeks answer for key pandemic question

When Maryland lifted its outdoor coronavirus mask mandate in response to new federal guidance, some public health experts were quick to point out it was still unclear whether the vaccines, effective at staving off illness and death, prevented people from transmitting the virus.

A study underway at the University of Maryland, College Park and about 30 other colleges and universities — from Washington to Florida, Texas to Minnesota — seeks the definitive answer.


The U.S. Centers for Disease Control and Prevention in an April 2 science brief said that “a growing body of evidence” suggests fully vaccinated people are less likely to have asymptomatic COVID-19 and are unlikely to transmit the disease. “However, further investigation is ongoing,” the brief read.

“This is the study that I hope will demonstrate that that’s true,” said Neil Sehgal, principal investigator for the Maryland site of the study, dubbed “Prevent COVID U.”


Sponsored by the National Institutes of Health, the university study comes amid states loosening or rescinding coronavirus related-restrictions. On Wednesday, Maryland Gov. Larry Hogan said he would lift capacity restrictions starting Saturday and, once 70% of the population received at least one vaccine dose, an indoor mask mandate.

The study’s conclusion could have implications about who should continue to wear face masks as people return to public life. The CDC on Thursday significantly eased mask-wearing guidance, saying vaccinated people can stop wearing them in most indoor and outdoor settings.

“It’s the most significant remaining question about COVID-19,” said Sehgal, who’s an assistant professor of health policy and management. “We need to know what risk vaccinated people pose to others, other vaccinated and unvaccinated people.”

Participants must be 18 to 26 years old, enrolled at a participating institution and not have been infected with COVID-19. They have to swab their noses everyday for about four months, complete daily questionnaires about symptoms on an app and get their blood drawn three times, including once at the beginning to determine if they’ve had the coronavirus, according to a study description.

Participating students also identify close contacts, like roommates, who they could easily spread the virus to if they contracted it. Those close contacts will be asked to participate “because testing the vaccine’s effectiveness to reduce and/or prevent transmission requires measuring spread of the virus to others,” the description says.

Nasal swabs are batched and sent to a centralized lab to test the “viral load,” or the amount of virus, in someone’s nose. The viral load is indicative of how likely a person is to transmit the coronavirus or any respiratory virus. Swabs also will undergo genomic sequencing to determine what effects, if any, coronavirus variants have on the effectiveness of vaccines at preventing infection and transmission.

If someone contracts COVID-19, the swabs will tell researchers how much virus is in their nose. Having close contacts swab their noses and get their blood drawn twice if a trial participant contracted COVID-19 will show researchers whether a vaccinated person can transmit the virus.

“If you have a lot of virus in your nose, then you’re likely to spread it into the environment around you,” Sehgal said.


Those conducting the study hypothesize that once someone is vaccinated “they’ll present less virus in their nose and they’ll be less likely to be infectious,” he said.

Maryland is among the first schools to launch its part of the study, according to Sehgal, and the university began enrolling students the first week of April and expects to conclude in August. Other schools expect their trials to roll into the fall, Sehgal said. As a result, preliminary results from the study are possible late in the summer with final findings by the end of 2021.

“There’s a lot of evidence to suggest there’s very little risk of transmission when you’re fully immunized,” said Dr. Chris Beyrer, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. “That study will give us the clear answer.”

So far Sehgal has enrolled 60 students, with hopes of getting 90 more participants.

Among those inspired to join was Elizabeth Keller, 21. She’s a junior public health major on the pre-med track who learned about the study from a professor.

Every day, the Severna Park native wakes up and swabs her nose — just another addition to the morning routine. Occasionally, she shuttles the samples to a lab across campus or goes there to get her blood drawn.


It’s a small price (participants are compensated up to $1,000 at Maryland) to pay for being able to contribute to a big scientific question, one that could shape how the country emerges from the coronavirus crisis, she said.

“Even if it’s inconvenient for me at this time,” Keller said, “hopefully because of this research they will produce data that’s important for the greater good and will help society move forward in this pandemic.”

As a pre-med student, Keller said, “all we do is study.” But she also finds time to work as a nanny in Washington, D.C., and to be a part of the university’s Club Sailing program, which finally has traded Zoom calls for in-person meetings.

Breaking News Alerts

Breaking News Alerts

As it happens

Be informed of breaking news as it happens and notified about other don't-miss content with our free news alerts.

Before finals began May 12, students started gathering on campus, she said. Six-foot circles and Adirondack chairs have been placed around the campus mall for people to congregate safely.

College students live dynamic lives in close proximity to each other and are known to socialize, making them the perfect demographic to study, Sehgal said.

Because young adults were only recently made eligible for the vaccine, researchers expect to be able to study both vaccinated and unvaccinated people, Sehgal said. Furthermore, universities already stood up testing infrastructures, which means there was a built in mechanism to detect virus spread and students already were used to having their noses swabbed.


Sehgal has made clear to participating students they can get a vaccine when it becomes available to them, allaying the concerns of some, like Keller, about having to wait longer to be protected from the illness.

The implications of this study have grown, Sehgal said, as he and other public health experts believe the country is unlikely to reach herd immunity this year.

He’s eager to return to the classroom to teach his students, all of whom will be required to vaccinated if they want to return to campus for the fall semester. But like others, he wants to know better what precautions will remain.

“I want to know if they’re all vaccinated, or the majority are vaccinated, can I teach with my mask off?” he said. “And this is the study that’s going to tell us that.”