Q&A: Is There a Way to Find Out If Your Vaccine Is Working?

In this week's edition of the Covid Q&A, we look at how to know whether a vaccine is working. In hopes of making this very confusing time just a little less so, each week Bloomberg Prognosis is picking one question sent in by readers and putting it to an expert in the field. This week's question comes to us from Bill in Westland, Michigan. Bill wants to know if there's a way to know whether his vaccine is working. Bill asks:

Is there a way for an individual to test their Covid-19 vaccine's efficacy after the second shot?

What a great question! More than 133 million doses of Covid vaccines have been administered in the U.S. We know from large clinical trials that those vaccines work for the vast majority of people, but not everyone. The double-dose Pfizer and Moderna vaccines were shown to have efficacy rates of about 95%, while the single-shot Johnson & Johnson vaccine had a rate of 72%. (Click here to read a previous Covid Q&A on vaccine efficacy.)

So how do you know if yours is working?

It would be nice if there were a test you could take after vaccination that told you conclusively whether you were protected from Covid-19. But unfortunately it's not that simple, says Robert Murphy, an infectious- disease expert at Northwestern University.

“There is no way to reliably do this with the available commercial tests,” he says.

It seems logical that you would be able to take an antibody test to figure out whether you had developed immunity to Covid, but the tests weren't created to do that, he says.