WHO has recommended 5 doses of tetanus toxoid for childhood immunization: the primary series of 3 doses of DTP3 (DTwP or DTaP) in infancy (age <1 year), with a booster dose of a tetanus toxoid-containing vaccine ideally at age 4-7 years and another booster in adolescence, e.g. at age 12-15 years. However, it has also advised a sixth dose in early adulthood to provide added assurance of protection throughout the childbearing years, and possibly for life [1].

The choice of primary schedule as well as of the number and timing of boosters varies considerably among countries, often reflecting national epidemiological, programmatic and economic considerations. Why a booster is given at 16-24 months? As far as protection against tetanus is concerned, a primary series of three doses provide almost 100% protections that last at least for 3-5 years. After that boosters are needed since antibodies to tetanus decline over time and hence regular boosting is needed to ensure adequate levels of antibodies during any apparent/inapparent exposure to tetanus bacilli/toxin. Similarly, for diphtheria, the average duration of protection is about 10 years following a primary series of 3 doses of diphtheria toxoid [2]. Therefore, revaccination of adults against diphtheria and tetanus every 10 years may be necessary to sustain immunity in some epidemiological settings. To compensate for the loss of natural boosting, industrialized countries add childhood boosters of diphtheria toxoid to the primary immunization series of infancy. The optimal timing for and the number of such booster doses should be based on epidemiological surveillance as well as on immunological and programmatic considerations. Considering the current epidemiology of diphtheria in India (i.e. low-endemic), a booster against diphtheria is desirable, but not mandatory. Boosting at the age of 12 months, at school entry and just before leaving school are all possible options [2]. However, the case is entirely different with pertussis, where a booster during second year of life is a must following completion of primary series of vaccination. When given in the second year of life, this booster will improve protection following primary immunization if a less effective vaccine (wP or aP) is used, thus preventing early accumulation of susceptible individuals [3]. The timing of this booster should also provide an opportunity for catch-up vaccination and allow for the use of a combination vaccine containing both pertussis and Hib antigens. These are the reasons why a booster of DTP is recommended at 16-18 months by different authorities in India. In fact, CDC/ACIP have also recommended the same schedule [4].

IAPCOI has also recommended 6 doses of tetanus containing vaccines, the last one at 10-12 years, preferably Tdap/Td. Thereafter, no further need of any boosters as far as tetanus is concerned.

Administration of boosters more frequently than indicated leads to increased frequency and severity of local and systemic reactions as the preformed antitoxin binds with the toxoid and leads to immune-complex mediated reactions. Arthus reaction (type III hypersensitivity reaction) is an example of immune-mediated reaction which occurs rarely after vaccination but can occur after tetanus toxoid-containing or diphtheria toxoid-containing vaccines are used too frequently.

There is no need to offer two doses of TT or Td to every pregnant mother. Similarly, TT/Td boosters are not indicated in all cases of wound management. The sole deciding criterion is the past history of tetanus immunization of the individual. WHO has in fact issued comprehensive guidelines for administration of TT/Td to pregnant women [1]. In countries where maternal and neonatal tetanus remains a public health problem, pregnant women for whom reliable information on previous tetanus vaccinations is not available should receive at least 2 doses of tetanus toxoid-containing vaccine (normally dT) with an interval of at least 4 weeks between the doses. To ensure protection for a minimum of 5 years, a third dose should be given at least 6 months later. A fourth and fifth dose should be given at intervals of at least 1 year, e.g. during subsequent pregnancies, in order to ensure long-term protection. For women who have received 3 primary doses in infancy, two doses during the 1st pregnancy are indicated. The 2nd pregnancy requires 1 more dose and gives lasting protection for the reproductive years. For women who have received three doses and 1 booster in childhood, 1 dose each in the first and second pregnancy provide lasting protection.  In women who have received 3 primary doses and 2 childhood boosters only 1 dose in the first pregnancy provides lasting protection. Women, who have received 5 doses of TT over a period of at least 2.5 years, get lasting protection for their reproductive years. For women who have received an additional adolescent booster, in addition to the 5 childhood doses, no further doses are necessary in pregnancy.

Evidence suggests that tetanus is highly unlikely in individuals who have received 3 or more doses of the vaccine in the past. Depending on the severity of the injury and on the reliability of the history of previous tetanus vaccinations, the vaccine should be given if the last dose was administered more than 10 years ago (or 5 years in the case of severe injuries).

References

1. World Health Organization. Tetanus vaccine: WHO position paper. Weekly Epidemiol Rec. 2006;81:198-207.

2. World Health Organization. Diphtheria vaccine: WHO position paper. Weekly Epidemiol Rec. 2006;81:24-32.

3. World Health Organization. Pertussis vaccines: WHO position paper. Weekly Epidemiol Rec. 2010;85:385-400.

4. Diphtheria, Tetanus, and Pertussis: Recommendations for Vaccine Use and Other Preventive Measures Recommendations of the Immunization Practices Advisory Committee (ACIP). Available from: http://www.cdc.gov/mmwr/preview/mmwrhtml/00041645.htm  Accessed on September 29, 2011.