UC San Diego Researchers Study Infection Risk after COVID-19 Vaccination


Zhuoying Lin

The nationwide clinical trial aims to answer whether vaccinated persons can transmit asymptomatic COVID-19 infections to others. The PreventCovidU study is recruiting UCSD students to participate in this four-month clinical trial. Researchers hope the result will provide crucial information to help shape the policy of in-person learning and travelling in the fall. 

While the Pfizer and Moderna vaccines have shown high efficacy against symptomatic COVID-19 infection, there still is a possibility that vaccinated people could contract asymptomatic infection. According to a clinical study of healthcare workers at UC San Diego and UCLA, 379 out of 36,569 individuals or one percent of the participants in the study tested positive for COVID-19 at least one day after the first dose of vaccination. The infection rate fell to single figures more than a week after the administration of the second dose. 

Source: The New England Journal of Medicine

It remains unknown whether a fully vaccinated person can become asymptomatically infected with COVID-19 and transmit the virus to others. Therefore, the Centers for Disease Control and Prevention suggests fully vaccinated persons to keep taking precautions — including wearing masks and maintaining social distancing until more knowledge is obtained. 

The new study being undertaken by researchers at UCSD and over 20 other universities across the country will attempt to answer this question. It will study the likelihood of a vaccinated person becoming infected with COVID-19 and whether they can transmit the virus to close contacts. In addition, the research will measure the viral load in nasal swabs and correlate this with the likelihood of transmission. The trial will run through spring and summer, and the results are anticipated to be published before fall so that schools can plan in-person learning accordingly.  

The nationwide study is co-led by researchers at Harvard University of Medicine, University of North Carolina and University of Nebraska Medical Center. Professor of Medicine at UC San Diego School of Medicine Dr. Susan Little will lead the study for the UCSD site.  

“What we’d really like to know is: in the com[ing] fall, can we tell people you don’t have to wear a mask because once you have been vaccinated, your risk of getting COVID-19 is near zero and your risk of getting asymptomatic COVID-19 is near zero. If you can’t get asymptomatic COVID-19, you can’t transmit, and you don’t need to wear a mask.” Little said. 

Researchers will study university students because their age demographic is at high risk of contracting and spreading COVID-19. According to the CDC Morbidity and Mortality Weekly Report, from June to August 2020, persons aged 20-29 have the highest COVID-19 incidence in the US and accounted for more than 20 percent of confirmed cases. Increases in COVID-19 positive cases among persons aged between 20-39 preceded increases among adults older than 60 by four to 15 days, suggesting that  younger adults are responsible for transmitting the virus to people who are more vulnerable to severe illness. 

In this clinical trial, a total of 12,000 students across the nation will be randomly assigned to two different groups. Half of the students will receive the Moderna vaccination at the start of the trial (the immediate vaccination group). The other half of the students will be vaccinated at the end of the trial (the delayed vaccination group). The delayed vaccination group is the control group in the study, and researchers will compare the rate of transmission between the two groups to assess the extent of protection the Moderna vaccine offers. 

Each student participant will be asked to collect their nasal swabs daily over the course of the trial. Daily COVID-19 testing is required because it is the only way to determine if a person develops asymptomatic infection. 

Each student volunteer will also be asked to invite at least two close contacts to participate in the study, which will increase the study participants to at least 36,000 people. Close contacts who consent to join the study will submit weekly questionnaires and get regular COVID-19 testing. 

“If I am in the immediate vaccination group, and I get tested every single day and I never had COVID but my close contact did, I will know two things,” Little said. “One, I didn’t infect him because I was tested everyday, and two, I was protected from getting COVID, so transmission didn’t not occur to me.”

Students ages 18-26 without previous COVID-19 infection or vaccination are eligible to apply. The UCSD site will recruit about 400 student participants, and enrollment started in early April. 

“The controversy of the study is asking people not to get vaccinated for four months,” Little said. “I want people to be aware that the study is entirely voluntary. We do inform people of the risks, so we want people to think about what their individual risks are and their family members’ and friends’.”

At the same time, the study will address research questions that have important policy implications. 

“This [asymptomatic transmission] is a monumentally important question but this is not something we want anyone to feel pressured into participating in. I want people to participate because they understand how important the question is; they are going to contribute to an incredibly important question and hopefully contribute to an outcome that will make all our lives better,” Little said. 

Students who are interested in participating in the study can register and find more information here

Photo courtesy of Erik Jepsen for UC San Diego.