Could you get the benefits of a COVID vaccine by having it injected into your butt instead of your arm, if for some reason you wanted to do that and were capable of finding a medical professional who would do it?
Let’s get straight to the point here: Yes. The COVID vaccine would still work if you had it injected in your butt. But for most people—not all people, but most people—this would be an anti-social thing to do, and for more than the obvious reason.
A posterior injection would work, as Dr. Robert Amler explains, because the available COVID vaccines are “intramuscular.” (Amler is the dean of the School of Health Sciences and Practice at New York Medical College and a former chief medical officer at the Centers for Disease Control and Prevention.) They will function wherever there’s enough muscle tissue to absorb them. (The Pfizer vaccine dose is 0.3 milliliters of liquid; the Moderna dose is 0.5 milliliters.) “From that tissue, the body and, basically, the bloodstream gradually passes it around,” Amler says. “As it passes around, the immune system detects it and says hey, there’s something here from someplace else.”
The glutes, like the deltoid muscles in shoulders, are typically large enough to trigger that immune response. So is the thigh muscle above the kneecap. But the delt is the vaccine administrator’s muscle of choice for logistical reasons. “It’s so easy to get to,” Amler says. “Most people don’t mind loosening their sleeve or unbuttoning their shirt slightly.” An injection site that can be accessed quickly, with a minimum of social awkwardness, means vaccines can be given out via an assembly line process in a public place.
Rene Najera, editor of the History of Vaccines Project at the College of Physicians of Philadelphia, also observes that most people have more fat in the backside area than they do in the shoulder or thigh. (Even when administering a shot in the shoulder, medical professionals might need to use a shorter or longer needle depending on how much skin, subcutaneous tissue, and fat a given patient has.) In general, intramuscular vaccines are preferred to those given subcutaneously, orally (like some polio vaccines), or intranasally (like some flu vaccines) because the concentration of immune cells in muscle makes for a stronger, bodywide response. (The oral polio vaccine, Najera says, more specifically protects the digestive system because that’s how polio enters the body; nasal flu vaccines are used to help prime children’s vulnerable respiratory tracts.) The earliest vaccines, for smallpox, were rubbed into patients’ skin after it was scraped with a blade; per Najera, the first vaccine commonly injected via syringe was the one Louis Pasteur created for rabies in the 1880s.
So, for most people, requesting a butt shot would mean wasting the time of the person giving the shot and the other people waiting in line for one. But there are potential vaccine patients who have had arms amputated, or who have a condition that has left them without sufficient deltoid mass to absorb a shot. For those people, Amler says, the thigh or buttocks could in fact be the best injection site. In some other cases, alternate sites might be preferable for more situational reasons. One is suggested by this problematic 1950s cartoon:
Some athletes might also prefer not to receive injections in their shoulders because of the soreness that they can cause. “In the ’80s, when I was at the CDC, we were vaccinating a Big Ten basketball team because they all got exposed to the measles,” Amler said. “We were all set to vaccinate and then I got a panicky call from the coach who said, ‘You’re not vaccinating my team, you are not gonna do that.’ We went back and forth—you know, when people don’t really listen to each other, it’s a darn shame, because we could have made a really short conversation if he had only explained exactly what his problem was, but I eventually figured it out. These guys are going to play basketball and you need a nice healthy shoulder in order to shoot hoops. And that’s all he was worried about—he just didn’t want it in the shoulder. And I said, ‘Coach, how about we give it in the leg or the buttocks?’ and he said, ‘Oh, that’s fine. That’ll be just fine.’ ”
The butt, according to multiple accounts, is also the site preferred by baseball players injecting performance-enhancing drugs. While it stands to reason that this is because it’s easier to play baseball with a sore backside than a sore shoulder, Slate was unable to confirm as much with an actual expert: Jose Canseco, Lenny Dykstra, and representatives of BALCO founder Victor Conte did not return requests for comment, while an employee at a new clinic founded by Biogenesis’ Anthony Bosch declined to address the issue. A spokesman for the United States Anti-Doping Agency noted that anabolic steroids are injected intramuscularly but did not respond to a follow-up question about why baseball players would use their buttocks rather than their deltoids to do so. A New York state phone number listed for Mitchell Report whistleblower Kirk Radomski was disconnected. Slate will update this post if any more information comes to light on the subject. Until then: If you can, take it in the arm.