Many negative tests followed by positive COVID antibody result

Dear Dr. Roach: I've had regular swab tests for COVID-19, which have always been negative. The last one was just a few days ago. I had an antibody test six weeks ago that also was negative, but my antibody test this time was strongly positive. I've been very careful about protecting myself and I haven't had any symptoms! I'm scheduled to get my first dose of vaccine tomorrow. What should I do? — C.W.Answer: With frequent negative swab tests and no symptoms, your likelihood of having had COVID-19 is lower than the average person in your community. But if your community has been hit hard, as most have, there is a good chance that you recently had an asymptomatic infection. The antibody test result you sent showed a strongly positive result using a very highly specific laboratory assay. Although it is possible this is a false positive test result, I suspect you had a true COVID-19 case so mild that you noticed no symptoms.You probably have some immunity against another case of COVID-19, but that immunity may wear off quickly. I recommend you get your vaccine as scheduled. It is safe to get the vaccine as long as you have no symptoms. However, people who were treated with a monoclonal antibody for their case of COVID-19 should wait 90 days before getting the vaccine.Dear Dr. Roach: I know someone who had the first and now second dose of the Moderna vaccine and did not get any of the side effects from either one of them. Does it mean the vaccine is not working, or does it mean their system is pretty strong? Everyone talks about the side effects, but no one mentions if you do not have side effects. Please clarify, as I am going to get my second vaccine this coming Saturday. — M.J.Answer: I often hear doctors and patients explain vaccine reactions, such as sore arm and fever, as evidence that "the vaccine is working." It's natural to worry that no reaction means the vaccine isn't working. However, that's not the case. Even people with no side effects whatsoever (most people have a little bit of a sore arm, at least) get benefit from the vaccine. The Moderna vaccine was 94% effective at preventing infections.It is true that people who have a history of COVID-19 infection are more likely to get a side effect like fever or fatigue. So, I wouldn't say that the person you know who had no side effects had necessarily a "strong" immune system. The immune system needs to be perfectly regulated to both protect you from invaders but also to avoid autoimmune reactions. But it does mean they are less likely to have had COVID-19 in the past.Part of the danger in COVID-19 infection is the body's immune and inflammatory response to the virus. I could speculate that those people who have very strong reactions to the vaccine might be those who are most likely to be at risk for severe COVID-19 complications. Speculation aside, vaccination is effective whether a person has side effects or not.&emsp;Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.