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As vaccine availability increases, some research participants are eager to know if they actually got vaccinated.

On social media, participants in have been hotly debating whether it's a good idea -- or ethical -- to unblind themselves by taking commercially available antibody tests. Many say they've already done so and used the results to help them decide whether to drop out and get a definitely active vaccine.

Others, like a 54-year-old pilot from Kentucky, are just curious.

"It's human nature to want to know," she told MedPage Today. "It's a personal choice, and I don't think it's harmful to the study."

Stanford University epidemiologist Steven Goodman, MD, PhD, doesn't share her lack of concern.

"There is no good scientific reason for someone to do this," he told MedPage Today. "I can understand why they want that information, but it can only serve to diminish the value of the trial. Getting tested is not right unless there is a pressing need for unblinding for health reasons."

Enrollment is complete in the 30,000-patient randomized, double-blind, placebo-controlled Novavax trial, which began in December in the U.S. and Mexico. The company later announced that the trial will include a "blinded crossover" component after it confirms that the vaccine is safe and effective enough to warrant an application for emergency use authorization. This means the trial participants will receive a second pair of shots. If they got placebo the first time, as one-third did, they will get the vaccine. The two-thirds who did get the real vaccine would then receive placebo.

It's not certain when the crossover shots will begin, and subjects may need to wait until April or later. The timing raises big questions for worried participants who are already eligible for the authorized vaccines or expect to become eligible soon.

One participant, a 39-year-old software engineer in North Carolina, recently took an antibody test before taking a brief plane trip that he couldn't get out of. "I thought it would make it less stressful," he said. (This man and the pilot from Kentucky asked not to have their names used.)

"My wife and I have been on our best behavior, not eating in restaurants or hanging out with people. It would be a real relief to have the confidence of knowing I do have some protection," he said. "I am more looking for some stress relief -- light-at-the-end-of-the-tunnel kind of stuff -- rather than, 'Hey, I'm going to go out and party.'"

Unfortunately for him, his antibody test suggests -- but doesn't definitively prove -- that he hasn't been infected by COVID-19 or exposed to a vaccine. Now, he is closely watching the timing of the crossover shots. "It's not impossible that I could be eligible sometime in April for one of those [authorized] vaccines. That would put me in a difficult situation."

COVID-19 antibody tests are not foolproof. However, "we know that clinical trials show that a majority of vaccinated people will produce antibodies at a level similar to those who have recovered from COVID by about 42 days. This has occurred across all vaccines that have published antibody data," said of the University of Alabama at Birmingham, who has , in an interview.

"Antibody testing should be a reliable indicator across those who have been vaccinated, although it can only be used to differentiate vaccination from recovery after infection by looking for antibodies against different parts of the virus. Antibodies against the nucleocapsid protein, found inside the virus, will only be found in those who have been infected, since the vaccines are targeted against the spike protein, which is [on the] outside of the virus."

Self-Interest Versus Science

The Novavax study has already had defectors -- those who chose to leave and be unblinded whether they got the vaccine or not. As of Feb. 1, , according to the company, and 55% of those were 65 or older. The company also reported its final enrollment numbers: 12.5% of participants were aged 65 or older. The goal was 25%.

The self-unblinding of participants spells trouble even if they stay in the trial, geneticist and cardiologist , of Northwestern University, told MedPage Today.

"The purpose of blinding the participants is so that they don't change their behavior and decide to take more risks in terms of getting COVID," she said. "We know vaccination will cause some people to take more risks. For example, it's possible that vaccinated people are less likely to wear a mask and not social distance. If one group of people is more likely to get COVID than the placebo group, this will skew the results. It could make the vaccine look less effective than it is."

Goodman, the Stanford University epidemiologist, said that those who unblind themselves via antibody tests "undermine the contributions of fellow trial participants and make this behavior seem acceptable by violating the trust within the trial, potentially weakening the ability to do other trials in a scientifically valid way as well."

Participants in these trials don't need to enroll purely from altruism, he said. But "if one is enrolling only for self-interested reasons, they shouldn't be enrolling. It is laudable to enroll in a trial and perfectly fine not to. But to enroll and then undermine it for personal benefit is a small act of scientific sabotage that should be strongly condemned."

What About Me?

I'm a participant in the Novavax trial myself, and earlier this month I signed an updated consent form disclosing the crossover component. As I wrote in a previous article for MedPage Today, I've been torn about whether to stay in the study -- potentially delaying my access to a vaccine -- or drop out.

As part of my reporting for this story, I got an antibody test myself in San Diego, where I live. The Kroger family of supermarkets has its rapid finger-prick antibody tests, so I dropped by one of its pharmacies and asked for a test, which cost a flat fee of $25. The results came in 15 minutes. To my surprise, since my first round of shots produced no side effects, I tested positive for both the , suggesting I did actually get the vaccine or had an infection without knowing it.

I'd been leaning toward staying in the trial regardless of the results since the crossover format guarantees I would get the Novavax vaccine at some point. And that the vaccine is a good product, although it may ultimately turn out inferior to the authorized vaccines.

I don't plan to change my super-cautious, borderline-paranoid anti-germ behavior. Relaxing would make me nervous, regardless of the antibody test results, and I don't want to somehow throw off the findings of the study. I am, after all, getting paid to participate.

The pilot from Kentucky is remaining cautious too. Her LabCorp antibody test results suggest she's either been infected or got the vaccine, so she believes she is in the clear.

Even so, "my behavior has not changed whatsoever since learning that I have antibodies. That really surprised me," she said. "I'm still double masking going in and out of work and while grocery shopping. I still feel uncomfortable being around non-mask wearers or people who wear their mask below their nose. Maybe it's because I believe that we should all be trying to do our best at controlling this pandemic, so I'm going to continue to do that."

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