Perhaps the most straightforward argument against getting an illicit extra shot is that the public doesn’t have enough data yet to be certain that it’ll make a difference, especially for people who have already had a two-dose mRNA regimen. Immunologists do broadly believe that boosting could offer some added protection in the short term, Ali Ellebedy, an immunologist at Washington University in St. Louis, told me. That’s not nothing, especially during a significant surge in the pandemic. But our outlook is limited by the fact that there’s virtually no data so far on whether non-immunocompromised people stand to gain any long-term protection. Pfizer shared some preliminary data from their clinical trials of booster shots in a recent earnings call, but they only show levels of antibodies in the blood—an imperfect proxy for how protected people actually are from sickness—and only track participants for a month after their third dose. Ellebedy would like to see six months’ worth of clinical data in order to make a judgment about whether the third shot truly changes things.

If those data become available before you’re eligible, you probably still won’t want to finagle your way into a dose before your turn, because skipping the line conceivably could hurt your protection in at least one way. Marion Pepper, an immunologist at the University of Washington, told me that overstimulating the immune system can make your body less adept at fighting off certain infections; scientists haven’t yet figured out whether that’s true for COVID-19, but Pepper sees it all the time in her work on malaria. Your immune system “needs some time and space to calm down in between seeing one infection and the next one” so that it can hone its pathogen-detection skills, Pepper said. Hitting it with another vaccine before it’s ready might not make it any better at fighting the coronavirus. (For immunocompromised people, whose bodies likely didn’t produce enough of an inflammatory response to get sufficient protection from their first two shots, this isn’t as much of a concern. “​​The priority there is to let them get their immunity at a good level,” Ellebedy said.)