Even if a trial participant got a private antibodies test and it was negative, they would have no way of knowing if they received the placebo or not. It could be that they got the vaccine and didn't develop sufficient antibodies or the antibodies declined over time. A positive test wouldn't necessarily mean they got the vaccine either. They could have had the placebo and then had a COVID exposure. I'm really not sure that it would hurt the study since different scenarios could explain the results.
You're right they can't know but that also why someone wouldn't want to think of it that they must not have gotten the vaccine. Unfortunately that is exactly what many will think because they are not medical professionals. The medical professionals who are conducting the study want to be able to control and study a person's immune system response. If they performed an antibody test and they were at the point of unblinding the study they can further investigate. What if the person was given the placebo but still produced positive antibodies? What if the person was given the vaccine and did not produce positive antibodies? And so on.
But if a trial participant gets an antibody test and it comes up positive they may assume they have the vaccine, drop out and live their life. Or stay in it assuming the whole time they got the vaccine. Or if they get an antibody test and it comes up negative they may assume they did not get the vaccine, drop out, live their life or wait it out and hope to get the vaccine elsewhere. Either way it's understandable why clinical studies hope to maintain the control themselves. It's more about the results being able to be reliable and in a controlled study way.
The person, as great as they've been, has already made the connection that they didn't get it and their spouse did. They have no idea but have made that assumption based on antibody tests administered outside of the study control. I can see how many of the thousands of participants might think the same way even though medically we don't know enough data on it.
I was interested in what that other person was saying and found out this from an FAQ from Duke Health:
"The studies use a design known as “randomized, double-blinded, placebo-controlled clinical trials.” This means that some people in the study will get the vaccine, and some will get a placebo (sterile salt water that does not have any vaccine in it).
The vaccine and the placebo will appear identical, so neither the volunteers nor the study doctors will know who receives the vaccine and who receives the placebo. This is what we mean by “blinded.” To ensure the safety of the participants, the research pharmacist, who is not a study volunteer or a study doctor, keeps a “code book” to record who received the vaccine and who received the placebo. The research pharmacist only uses this information in case of an emergency to protect the participant (for instance, symptoms of an allergic reaction).
During the study, the researchers will compare the numbers of participants who have taken the vaccine who test positive or get sick to the number of participants who have taken the placebo who test positive or get sick. If the vaccine is effective, the number of participants who receive the vaccine and who test positive or get sick with COVID-19 will be significantly
lower than the number of participants who receive the placebo and who test positive or get sick with COVID-19." "The vaccines and antibodies being tested in these studies aim to prevent a person from getting COVID-19. They must be tested on volunteers who do not have COVID-19 because our goal is to keep people healthy. Other studies of treatments may be offered to people who already have COVID-19."
I looked up a bit more and found LapCorp had the following "While the level of antibodies needed to be considered immune to SARS-CoV-2 is yet to be determined, ongoing vaccine trials and research should help answer this question. The test is also currently being utilized by the Centers for Disease Control and Prevention (CDC) for SARS-CoV-2 seroprevalence studies to understand the level of antibodies produced through natural exposure and infection with the virus."
I could be wrong but I think the issue is really a person taking a private antibody test outside of the trial and drawling their own conclusions from that.
