Needle length for vaccines should vary based on weight. You may want to ask for a bigger one — here's how.

syringe held by hand glove
While the standard needle size for vaccination is 1 inch, it's recommended that women over 200 lbs. and men over 260 lbs. get shots with 1.5-inch needles. (Getty Images) (Nicolae Toma / 500px via Getty Images)

Most people don’t want to think about the needle part of getting a vaccine any more than they have to — but you might want to start. Your weight may mean that you need a larger needle than you assumed, or even that your doctor or pharmacist may be providing you with.

According to the Centers for Disease Control and Prevention, it is recommended that women over 200 pounds and men over 260 pounds get shots administered using a 1.5-inch needle, while the needle size used for all other adults over 19 years old can range between 1 inch and 1.5 inches.

Why you may want a longer needle

Dr. Melanie Jay, who researches the treatment and prevention of obesity at New York University, tells Yahoo Life that intramuscular vaccines are meant to be delivered into the muscle, which lies under the deltoid fat pad. However, when there is a larger deltoid fat pad, a longer needle is more likely to reach the muscle.

“Because women have higher volumes of deltoid fat at the same body mass index, they may need longer needles than men at the same weight,” she explains. “So the real issue is not weight, it is the amount of deltoid fat, which is likely to be higher in people with obesity.”

The CDC’s weight guidelines, she notes, are just an estimate, as “people are built differently.” One person may have less fat in their arms than another, despite being the same weight.

It’s not just people with larger bodies who may wish to adjust needle size. According to Dr. Malathi Srinivasan, a clinical professor of medicine at Stanford University, “if someone is very thin, or they've had a lot of muscle wasting, or if they are an elite athlete and they just don't have a lot of cutaneous muscle, then you actually want to use a shorter needle, like a .5-inch, or .8-inch.”

Typically, “the injector makes a judgment based on how the deltoid area of the arm appears,” says Dr. Amesh Adalja, infectious disease expert and senior scholar at the Johns Hopkins Center for Health Security. “Weight is one guide, but it really depends on what the area looks like.”

How to speak up

You may want to advocate for a longer needle length when getting a vaccination, especially if you are concerned that you may need a larger needle than the one you typically receive.

“I think that people should advocate for themselves routinely for all of their medical care and bring up issues in a collaborative way that will let the person they're talking with engage with them,” says Srinivasan. “I would recommend a patient say, ‘I have a larger body, and I'm wondering what the best needle length would be so that you can get into the muscle.’”

Jay notes that there is a "systematic obesity stigma and bias in healthcare," which can stop people from getting the medical help they need. “I think that changes need to happen at both the individual level, with healthcare providers really listening to their patients with obesity and empathizing and, more importantly, at the system level where protocols need to be implemented but in a way that doesn't further stigma," she says.