Mysteries of the Tetanus Shot
Sean Nordt MD, PharmD, Stuart Swadron MD, Rob Orman MD and Ran Ran MD
- In a review of all tetanus cases in the United States, 70% of wounds were considered prone to tetanus, such as contaminated or puncture wounds, and 30% were clean wounds.
- Increased age leads to decreased immunity, and the elderly are at increased risk of clinical tetanus.
- A study measuring antibody titers at day 0 and day 4 after tetanus vaccination found no statistically or clinically significant change in titer levels.
- Patients who have not received the complete primary series of vaccinations and have a wound that is not clean should receive the tetanus immunoglobulin.
Tetanus is seen infrequently in the western world but it still accounts for much morbidity and mortality, including in neonates, in the developing world.
Tetanus is caused by Clostridium tetani. Tetanus inhibits the release of glycine and GABA. These are inhibitory neurotransmitters. This causes the classic opisthotonus and leads to respiratory arrest. Another Clostridium bacterium, botulism, inhibits the release of acetylcholine.
Opisthotonus is severe arching of the back. This occurs because the extensor muscles of the back are much stronger than the flexor muscles in the front. All of these muscles are firing and the back wins. This is not subtle. If you see this, also consider strychnine poisoning. Strychnine poisoning inhibits the binding of glycine in the spinal cord and presents similarly.
Do tetanus vaccinations work? Yes. The vaccination was first introduced during World War I. Prior to its introduction, about 1 out of every 300 soldiers contracted tetanus. There was a thirty-fold decrease in the incidence of tetanus in the subsequent two months. In the 1940s, it was introduced as a routine vaccination in children. Since then, the rate of tetanus has dropped thirty-fold in the civilian population.
The primary series of three vaccines during childhood educates your immune system to recognize the pathogen, and this is followed by a booster shot every 10 years for the rest of your life. Although this has not been well studied, the Centers for Disease Control (CDC) found that 100% who adhere to this regimen will have antibodies at a protective level.
Can people who have had the vaccine still get tetanus? Yes. Titer level is only one component: the pathogen burden and immune system function also contribute.
In a review of all tetanus cases between 2001-2008 released by the CDC, 70% of wounds were considered prone to tetanus, such as contaminated wounds or puncture wounds. 30% were clean wounds and there have been case reports of surgical wounds, using autoclaved instruments, resulting in tetanus.
When does immunity start to wane? Increased age leads to decreased immunity. In the United States, there have not been any neonatal cases of tetanus and only 1-2 cases in patients under 20 years old. The booster is very important in older individuals. Tetanus is a unique pathogen, and recovering from clinical tetanus doesn’t convey immunity. The tetanus toxoid is one of the most potent toxins known to man. The lethal dose is 2.5 ng/ kg. It is important to keep a supratherapeutic level of antibody titers, as it is important for protection. Diabetes, HIV, and prednisone can also weaken the immune response.
You are working at your Emergency Department on Saturday night. A 30-year-old male stepped on a rusty nail. He had all of his immunizations and boosters for college. Does he need to get a tetanus shot immediately or can he wait until Monday?
Irrigation and debridement of necrotic tissue are the most important intervention. Tetanus vaccine is terrific as primary prevention before an exposure, but it doesn’t do much as secondary prevention.
- Porter JD, et al. Lack of early antitoxin response to tetanus booster. Vaccine. 1992;10(5):334-6. PMID: 1574917. 31 adults had antibody titers measured at day 0 and day 4 after tetanus vaccination. There was no statistically or clinically significant change in titer levels. Clinical tetanus can develop within 3 days but it may take longer to develop.
- Should the person get a dose of tetanus immunoglobulin? In the United States, there are two indications for tetanus immunoglobulin. Immunoglobulin should be given if: 1) the wound is anything other than clean and simple; and 2) the patient must have an incomplete primary series with less than 3 doses of tetanus vaccine. In the rest of the world, for example in the United Kingdom, they try to estimate the risk of tetanus based on the wound characteristics such as puncture wounds, foreign bodies, significant devitalized tissue, heavy contamination, burns, or sepsis.
- What if the patient has never received tetanus vaccination or does not remember? About half of patients do not remember when their last tetanus booster was received. About 25% of patients who think they are up-to-date are not. If tetanus booster is provided based on patient recall, treatment will be incorrect about 40% of the time. Given that the tetanus booster is of questionable utility for secondary prevention, a better question is whether the patient has received their primary series. Were you born in North America? Did you receive vaccinations as a child? You can look to see if tetanus is included in the childhood vaccinations in his/her home country.
- If the patient has never received the primary tetanus series, they need tetanus immunoglobulin. They also need the tetanus vaccination series. The tetanus immunoglobulin is given in one arm and the vaccination is given in the other arm.
The tetanus booster is available as Tdap (tetanus diphtheria and pertussis) and Td (tetanus diphtheria). The CDC recommends that everyone receive a tetanus booster every ten years, and one of those doses should be Tdap after the age of 18 years. Pregnant women should receive Tdap with every pregnancy. Giving elderly patients Tdap is not cost effective but would reduce the likelihood of the patient developing pertussis by 25%. Tdap is twice as expensive as Td ($50 versus $25).
Who is likely to develop tetanus despite vaccination? Immunity wanes with age. Most of the cases of clinical tetanus happen in the elderly.
- Talan DA, et al. Tetanus immunity and physician compliance with tetanus prophylaxis practices among emergency department patients presenting with wounds. Ann Emerg Med. 2004 Mar;43(3):305-14. PMID: 14985655.
- Immunoglobulin levels were measured in nearly 2,000 patients. 5% of patients who reported that they were up-to-date on vaccination did not have protective levels of antibodies. This increases to 15% in patients who are not up-to-date. The CDC case series found that 12% of tetanus cases had completed their primary series but most of them were not up-to-date on their boosters. 3% of cases had received their primary series and were up-to-date on their boosters.
There is no herd immunity; tetanus is infectious but not contagious.
Don’t forget about tetanus in open fractures and ocular injuries. If you are worried about tetanus, metronidazole or penicillin are the recommended antibiotics.