Vaccinating obese kids: the long and the short of it

Studying the efficacy (effect under controlled conditions) and effectiveness (effect under real world conditions) of vaccines is a tricky business we've talked a lot about here. How do you know when someone has really gotten the vaccine? Just because you stuck the needle into them? That's a pretty good indication, but it might not be all the information you need. Their weight might be another. And the length of the needle used still another:

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. (Reuters)

I like to give reporter by-lines, but this one had sort of a garbled version of the science so I won't (for example, antibodies "kick start" the immune system). Not really important but it's nice to get it straight if you are going to bother to say it. At any rate, the outcome measured in the randomized trial was antibody response. Shorter needles produced a much lower antibody titer than the longer one. The vaccine was for hepatitis B and the level of antibody needed for protection is unclear, but based on estimates there was enough antibody to protect the subject with either needle length. So we don't know if the difference in antibody response is epidemiologically significant, nor do we know the reason. Is it because the vaccine doesn't get to where it needs to or that obese kids don't respond as well?

We don't know, nor do we know how many doctors follow CDC's advice to use longer needles on obese patients. Lots of vaccinations are given by nurses and it's not clear they have even heard CDC's advice on the matter. Or, for that matter, that doctors have either.

Just another little variable to consider when we are trying to figure out how well vaccines work. Because it wasn't hard enough.

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I don't understand the idea here. How does using a longer needle increase vaccine effectiveness? The idea is to get it into the blood. What does it matter if the needle is blue/red/long/short, etc?

Alex: You don't want to get it into the blood. You want to get it to where antigen presenting cells in the immune system will encounter it. That's either in the dermis (layer below the dead layer of your skin) or in the muscle. You don't want to get it into fat.

I'm not sure that "kick start" is so bad. Don't some (though not all) vaccinations just cause the immune system to be "pre-programmed" to create antibodies that it would eventually create anyway? Maybe "jump start" would have been a better term.

Jack H: He says the antibodies do the kick starting, not the antigens.

Alex & revere: many (if not all) vaccines are deposited into the muscle and they leak out slowly into the circulation where the APCs present them to the naive T cells. If the fat is too thick i.e. greater than the length of the needle, then you can't get to the muscle. Remember how bad your last tetanus booster shot in your shoulder hurt?

So what about if one got (finally) one's 2009H1N1 vaccination and didn't even feel the needle go in? (A first, even though p.h. nurse's shots are usually near-painless.)

@Angela: I don't remember any of the vaccinations I got. That was a while ago. I especially don't want to remember the painful ones. I remember going to the doc thinking about something pleasant just to avoid feeling the pain. So if tetanus was one of the painful ones, I definitely don't remember.

The article is limited to obese adolescents, mainly female. Most vaccines are issued to children, and obese children have a thinner layer of fat than adolescents, so I doubt shots to children have as much trouble reaching the muscle as obese adolescents and adults (especially females who might not have as much muscle as men, note the study included 22 females and only 2 males, and this seems a SSS).

What vaccines are we talking about here anyways, tetanus, HPV, flu, shingles, etc? Military and those working abroad may get vaccines for some exotic diseases, but the military probably does not have as many issues with obesity.

@Alex: how long has it been since your last tetanus? Adults should have boosters every 10 years, more frequent with at risk occupations. See if you notice it the next time you get one. It's not the pain from the injection, but the deposited material pressing against muscle fibers that causes the pain.

@Paula: I remember mine, the injection didn't hurt because I had a small needle. I did have pain from both my seasonal and H1N1. Did your vaccine administrator tell you to move your arm a lot to help distribute it?

Thanks, Angela. Um, no she didn't. And I was so amazed not to have felt the needle at all (I don't mean just no pain), and at first so impressed with the p.h. nurse's (presumed) skill and later so worried whether, after months of anxiety to get the vaccine, perhaps I'd not actually got it at all, that moving the arm didn't even occur to me. As for pain, that's rare, in my experience, with flu vaccines.

Interesting article Revere.

Angela: I think that the guidelines for tetanus boosts (i.e. after primary set of inoculations or vaccination) are in deed once every 10 years but only twice. I think that by the second boost you develop lifetime imunity. Specific risk groups might be subject to different guidelines.

Tetanus booster vaccination (Td)is recommended every 10 years for one's entire lifetime. Recommendation changes to a shorter interval depending on travel plans or certain types of wounds sustained.

I got a tetanus booster in December (I was seeing my doctor anyhow, and it had been 9.5 years since the last one, so I asked for it). It didn't hurt particularly; maybe a little more than this season's flu shots. A bit of soreness after.

(I'm plump but also well-muscled, if that makes any difference.)