Children are less likely to develop bad reactions to the DTaP vaccine, a routine immunization shot that protects against diphtheria, tetanus and pertussis, or whooping cough, if they get it in their thigh instead of in their arm, a new study shows.
The research looked at more than a million children who were given injections of the vaccine. In many cases it causes some degree of redness or swelling around the injection site, which typically goes away after a day. But in rare instances a child can develop a more pronounced reaction, like severe pain or a swollen limb, that may require medical attention.
In the new study, which was published in the journal Pediatrics, researchers found that children between the ages of 1 and 3 who were given the DTaP vaccine in their thigh instead of in their upper arm were around half as likely to have a local reaction that warranted a visit to a doctor, nurse or emergency room. Previous studies of children who received the vaccine between the ages of 4 and 6 found that they, too, had a lower likelihood of developing a local reaction requiring medical attention if they got the shot in their thigh instead of in their arm.
Why the vaccine would be less harsh on the thigh than the arm is not known for certain. But one possibility is simply that in children at that age, the thigh muscle is much larger than the deltoid, the muscle in the upper arm where shots are typically administered. If any inflammation ensues, it has more room to diffuse in the thigh, said Dr. Lisa A. Jackson, the lead author of the study and a senior investigator at the Group Health Research Institute in Seattle.
“In little kids the upper arm is very tiny,” she said. “You’re injecting the same volume of vaccine in the upper arm as in the thigh, which is a larger area. I think it’s just that it’s a larger muscle mass.”
The benefits, however, may not extend to other immunizations. The study, for example, also looked at shots for influenza and hepatitis A, and in those cases there was no meaningful difference between vaccinating in the arm or thigh for either toddlers or children ages 3 to 6.
In many cases, doctors choose where to administer a shot according to their own preference. But in the case of DTaP, at least, it makes more sense in general to give the shot in the thigh, Dr. Jackson said.
“Unless there’s a compelling reason not to, I would say veer toward giving the DTaP vaccine in the leg,” she said. “There’s less chance of a concerning reaction if you give it in the thigh versus the arm. So that should be the normal practice.”
Dr. Jackson stressed, however, that the absolute risk of a child having a reaction severe enough to warrant medical attention is still quite small, regardless of whether the shot is given in the arm or leg. The study found that it occurred in less than 1 percent of vaccinated children over all.
Well: For DTaP Vaccine, Thigh May Be Better Injection Site Than Arm
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Well: For DTaP Vaccine, Thigh May Be Better Injection Site Than Arm
