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By David C. Holzman
I didn’t think it was a big deal. I’d stepped on a shell in Wellfleet Harbor, and it had sliced into my foot, and drawn blood. Heck, I didn’t even think tetanus bacteria hung out in salt water — they like soil, especially if the icing atop its cake is manure. But my anguished Jewish mother was all “get over to AIM [the local health clinic] right away, before lockjaw has a chance to set in.”
Of course, the power of the Jewish Mother to inflict fear and guilt is legendary. So I ultimately hauled my derriere over to AIM. But there was a problem.
I had first learned I was allergic to tetanus shots when I was 17 — two decades earlier. I don’t remember what I’d stepped on, but I’d ended up having to go back to AIM a couple of hours after the tetanus shot, so that they could check out the hives that had sprouted from feet to nether regions to scalp. While I was in no immediate danger, I was advised that the specter of anaphylactic shock loomed over any future tetanus shots.
But now at AIM once again, I wasn’t anticipating a problem because a year after the hives, I’d stepped on something on a trip in England. But the nice doctor who had given me that injection swore that he’d quit the profession if the preventive shot he’d given me with the tetanus shot failed to protect me from hives, or any other reaction.
So I figured the docs at AIM would also know what to give me to prevent a reaction. But instead, they gave me some gobbledygook about how I should really wait until I got home — which was Washington, D.C. at the time — and let my own doc give me the shot. But the docs at Group Health, my then-HMO, were equally stymied by my predicament.
At the time, I was the medical writer for the now-defunct Insight Magazine, a news weekly. And as soon as I had returned to DC, I had gotten to work on an article on one of the first experiments in human gene therapy. It was August of 1990, and I was interviewing one of the investigators, R. Michael Blaese, then chief of the cellular immunology section at the National Cancer Institute. Blaese was attempting to cure an immune deficiency by inserting functional adenosine deaminase genes into certain white blood cells.
I knew that blood turns over monthly. So I asked Blaese if the patients were going to have to receive the gene therapy every month. No, said Blaese, explaining that these particular white blood cells are “memory cells,” immune cells that last for decades. That, he added, is why people who have had the normal series of tetanus shots, including boosters in adolescence, often never need another.
That got my attention fast. And while I hadn't exactly been worrying about lockjaw, because I thought the bleeding had been copious enough to wash out any tetanus bacteria that might have gotten into my foot, if they actually inhabited salt water. Nonetheless, I jumped at the chance to resolve this business once and for all, so I told Blaese my story.
Blaese told me that I could simply have my tetanus antibody titer taken. My tetanus antibody titer turned out to be high enough to put my mother’s worries to rest.
The Booster Question
Fifteen years later, after my new Boston-based doctor suggested a tetanus booster, and I informed her of my allergy, and my previous antibody titer, I had a second antibody titer taken. I had plenty of antibodies: 5.48 IU/ml (anything over 0.15 IU/ml is considered a “healthy, immunized” level). My guess is that I will never need another tetanus shot. And you probably don’t, either.
A conversation with an eminence in the field of vaccines supports that statement. William Schaffner, MD, is a professor of preventive medicine in the Department of Health Policy, and a professor of medicine in the Division of Infectious Diseases, at Vanderbilt University School of Medicine in Nashville. He’s also a longstanding member of the Centers for Disease Control Advisory Committee on Immunization Practices.
The last time the committee focused on the tetanus component of the tetanus, diphtheria, and pertussis vaccine, 15 years ago, “A substantial rump group of us reviewed the literature and concluded that the current recommendation, boosters every ten years after the initial three dose inoculation series, comes from an extraordinarily conservative position,” says Schaffner. “You could immunize an infant, give an adolescent a booster, and maybe another at age 50, and be fine.”
“There is some discussion about whether this extraordinary protection you get can actually wane,” says Schaffner. "That may be true, but it's super rare.”
Nonetheless, I wondered if my ample antibody titer might result from the fact that I play in the dirt, and have stepped barefoot on thorns in my yard on more than one occasion. Definitely not, said Schaffner, noting that tetanus can actually recur in unvaccinated people who survive it. Yet, there is a study showing detectable serum levels of tetanus antitoxin in non-immunized Indian subjects, according to Stuart Johnson, of Loyola University Medical Center. I’ll reserve judgment on this question.
The cause of lockjaw is not the infection, per se, but a toxin the bacterium produces. Symptoms appear three to 21 days post-exposure, when the toxin, tetanospasmin, gets into the neuromuscular junction. There, it “stimulates muscles to contract fiercely,” says Schaffner. Patients can be managed through the symptoms, which can last several weeks, by intubation, putting a tube in the bladder to prevent urinary retention, and by monitoring blood pressure, which can fluctuate widely. Heart monitoring is also important, as under tetanospasmin’s influence, that organ is prone to abnormal rhythms. Patients are put into drug-induced comas, “so that you are psychologically spared this illness,” says Schaffner.
After around three weeks, the toxin is metabolized and assimilated, permitting the neuromuscular junction to function normally again. Without the toxin, the bacterium, Clostridium tetani, would be innocuous. Therefore, antibodies generated by the vaccine bind the toxin, not the bacterium.
Absent the vaccine, lockjaw would be common, as it still is in the developing world. The bacterium appears in anywhere from 2 percent to one quarter of soil samples, says Schaffner. Like dung beetles, C. tetani thrives on fecal matter. Unvaccinated, one could get tetanus by cutting oneself in one’s kitchen, from bacteria that came in on the vegetables, or that blew in on dust, Schaffner said. And spores can survive in saltwater, so my mother’s worries were not entirely unwarranted.
But today, only about 20-30 cases occur annually in the U.S. “Virtually all of those cases will occur in unimmunized or inadequately immunized individuals,” says Schaffner. Half of those are in people over age 60, and most of the latter are women, he says, explaining that very few women of a certain age ever served in the army, were tetanus vaccination was de rigeur.
But in the developing world, 275,000 neonatal cases occur annually, which is a significant chunk of the 11 million annual childhood deaths worldwide. (In the developing world, most who contract the disease die of it; in the U.S., survival is common.)
So, should people get their antibody titers taken, or should they just get tetanus boosters? “When in doubt, vaccinate,” says Schaffner. “Tetanus [vaccine] is an ouchy when you get it. But other than that, it’s an extraordinarily safe procedure.” Moreover, from a public health point of view, Schaffner says we lack laboratories that can perform the antibody tests, the reagents, and people who are capable of running the antibody tests, he says.
Polly Matzinger, the National Institutes of Health immunologist who is half of the team responsible for the danger model of immunology (see explanation below), disagrees. Demand for the test would create the supply, she says. Moreover, the last time she got a tetanus shot, her arm hurt for a year, and she says she would never get one again.
(Note: According to the danger model, instead of distinguishing self from non-self, the immune system senses danger signals from tissues stressed by injury, infection, toxins, or other stressors, and attacks microorganisms associated with that stress.)
David C. Holzman writes from Lexington, Mass., on science, medicine, energy, environment and cars. He is Journal Highlights editor for the American Society for Microbiology and won a Plain Language/Clear Communication Award in 2011 from the National Institutes of Health.
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