Negative tests followed by positive antibody result

Dear Dr. Roach: I’ve had swab tests for COVID-19, which have been negative. The last was a few days ago. I had an antibody test six weeks ago that was negative, but my antibody test this time was positive. I haven’t had symptoms! I’m scheduled to get my first dose of vaccine tomorrow. What should I do? — C.W.

Dear C.W.: With frequent negative swab tests and no symptoms, your likelihood of having had COVID-19 is lower than the average person. There is a chance you had an asymptomatic infection.

The antibody test result showed positive using a laboratory assay. I suspect you had a true COVID-19 case so mild that you noticed no symptoms.

You probably have some immunity against another case, but that immunity may wear off. I recommend you get your vaccine as scheduled. It is safe to get the vaccine as long as you have no symptoms.

Dear Dr. Roach: I know someone who had the Moderna vaccine and did not get any of the side effects. Does it mean the vaccine is not working, or does it mean their system is pretty strong? — M.J.

Dear M.J.: I often hear doctors and patients explain vaccine reactions as evidence “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 get benefit.

It is true that people who have a history of COVID-19 infection are more likely to get a side effect. So, I wouldn’t say that the person you know who had no side effects had a “strong” immune system.

I could speculate people who have strong reactionsmight be those who are most likely to be at risk.