Large trial underway to determine if vaccinated people can catch, transmit COVID-19

Speaking at a White House coronavirus task force briefing on Friday, Dr. Anthony Fauci says scientists are trying to answer the two most pressing questions for millions of Americans already fully vaccinated against COVID-19: Can they become infected without showing any symptoms, and if so, can they transmit the coronavirus to someone else?

Fauci said at the White House coronavirus briefing Friday that a large trial is under way involving 12,000 college students at more than 20 universities.

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"This is a question of extreme importance," he said. "This will help inform science-based decisions about mask use and about social distancing post-vaccination."

Half the students will get the two-dose Moderna shot and the other half will initially serve as a control group, while getting the same vaccine four months later.

All the students will keep an electronic diary, swab their noses daily and provide occasional blood samples. They’ll also provide the names of close contacts. Fauci says it may take about five months to get answers.

Currently, the U.S. Centers for Disease Control and Prevention say it is possible that "a person could be infected with the virus that causes COVID-19 just before or just after vaccination and still get sick."

That’s because it typically takes several weeks for the body to build immunity (protection against COVID-19) after vaccination, according to the health agency. 

In February, researchers at the National Institutes of Health say they found evidence that people who have been previously infected by the novel coronavirus appear to be protected against reinfection, though the extent to which that protection holds up against emerging variants remains unclear. 

"The data from this study suggest that people who have a positive result from a commercial antibody test appear to have substantial immunity to SARS-CoV-2, which means they may be at lower risk for future infection," said Dr. Lynne Penberthy, associate director of NCI’s Surveillance Research Program, which led the study.

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"Additional research is needed to understand how long this protection lasts, who may have limited protection, and how patient characteristics, such as comorbid conditions, may impact protection. We are nevertheless encouraged by this early finding," Penberthy said.

NIH researchers also noted that the exact duration of antibody protection is unknown, even though their findings support the idea that having the antibodies helps protect the individual from subsequent infection.

How long immunity lasts from natural infection is one of the big questions in the pandemic. Scientists still think reinfections are fairly rare and usually less serious than initial ones.

Still, the CDC says people who get vaccinated won’t test positive for COVID-19 on viral tests. 

"If your body develops an immune response—the goal of vaccination—there is a possibility you may test positive on some antibody tests," the CDC says.

Antibody tests indicate you had a *previous infection* and that you may have some level of protection against the virus, according to the health agency.

The CDC also added that people who have recovered from COVID-19 should get vaccinated. 

"You should be vaccinated regardless of whether you already had COVID-19. That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19," the CDC said.