For obese, vaccine needle size matters

Kudos, fatsos.

Our ever-expanding waistlines may have outgrown the doctor's needle, researchers say, in what could be another casualty of the obesity epidemic.

In a new study, the researchers report that using a standard 1-inch needle to immunize obese adolescents against hepatitis B virus produced a much weaker effect than using a longer needle.

"As obesity rises in the US, we need to be aware that the standard of care may have to change to protect obese youth," study co-author Dr. Amy Middleman of Baylor College of Medicine in Houston told Reuters Health.

Over three years her team vaccinated 22 young women and two young men in the shoulder, randomly assigning them to be injected with either a 1-inch or a 1.5-inch needle.

Once injected, vaccines trigger production of small molecules called antibodies, which kick-start our immune system if we are ever attacked by the virus again.

The two groups turned out to have different antibody counts depending on the needle used. In those injected with the short one, the number was almost halved.

Although everyone in the study had enough antibodies to be considered protected against hepatitis B, a lower count generally means a less robust response.

"It gives us more evidence of the importance of choosing the right needle length," said Middleman, "because we just don't know what the impact could be in other vaccines."

But could any needle be long enough to get it through your thick heads that you are too darned fat?