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Immunization Dialogue

Indian Pediatrics 1999; 36:198-200

Role of DPT or TT Vaccines After Injury or as Prophylaxis


Q. The incubation period in tetanus is 3-14 days. Tetanus toxoid as such or as a component in DPT or DT vaccines is administered for active immunization against tetanus. It takes. about 2-3 weeks period to produce the antibodies. These vaccines do not provide instant protection which is provided by Tetanus Immuno Globulin (TIG).

Depending upon the nature of the injury and the immunization status, TIGc mayor may not be required. What is the rationale of administration of IT or DPT vaccine without simultaneous 'administration of TIG following. an injury or as prophylaxis before surgery in fully immunized, partially immunized or unimmunized person?

Ans. Tetanus prophylaxis by immunization may be considered as pre-exposure and post- exposure types. In pre-exposure immunization the principle is to ensure that protective antibody level is already present in body flu- ids any time when injury takes place, with the attendant risk of introduction of spores of Clostridium tetani. Routine vaccination with DPT using 3 doses for primary and 2 doses for booster immunization is the best example of pre-exposure prophylaxis. Another common example is the vaccination of pregnant women in order to provide sufficient passive protection to the neonate. In previously unimmunized women at least 2 doses should 'be given with a minimum of 4 weeks interval and the last dose should be given with sufficient time interval to allow the development of high antibody level in order to be transferred transplacentally. At the ,next pregnancy another dose is necessary as booster. Dr. Yash Paul alludes to prophylaxis before surgery (where nosocomial tetanus is a problem). Like in pregnancy here also 2 doses and sufficient intervals are necessary.

Post-exposure prophylaxis is given following injury. The injury may be associated with the risk of introduction of tetanus spores. Clean minor injuries are those with very slight, if any, risk of contamination, such as cuts while indoors especially with clean instruments. In persons who have received 3 or more doses of tetanus toxoid in the past, either as monovalent (IT) or as combination (DT or DPT), with clean minor or other forms of in- jury, no passive immunization is needed. .If the interval between the last dose of vaccine and a clean minor injury is more than 10 years, then one booster dose is recommended. If the wound is puncture, crush or bum, or contaminated with soil, animal or human faeces, etc., then a booster is recommended even if the interval from the last dose of vaccine is less than 10 but more than 5 years. In these cases the immunological memory results in the booster dose inducing a very rapid rise of antibody within 2 to 3 days. The principle here is that there should be high levels of antibody when the tetanus toxin is-released by the organisms. If the wound is likely to have been heavily inoculated with tetanus spores we need very high antibody levels and therefore a booster is good even if only 5 years have lapsed after the previous last dose of toxoid, although at that time we would expect sufficient antibody to take care of small amounts of toxin.

In persons previously partially immunized with only 1 or 2 doses, one booster dose is to be given after clean minor injury at any interval from the last dose. If the total adds to only 2 doses, then 4 weeks later a third dose completes primary immunization. After any other types of injuries (see above) both passive (tetanus immune globulin) and active (one dose of IT immediately and another 4 weeks later) immunization should be given. In such situations we cannot guarantee adequate levels of antibody at the time of injury or even within the incubation period of tetanus. Therefore passive introduction of antibody is necessary to give protection for the present and a full course of immunization for future.

In previously unimmunized persons with clean minor injury the risk of tetanus must be considered and weighed against the cost of passive immunization. Usually, such injuries are not associated with risk, but the opportunity should be used to commence active tetanus immunization with one dose immediately and further doses later. In such persons with other types of injuries, obviously both passive and full active immunization must be offered. When it is not possible to obtain reliable history of previous immunization, the person should be considered unimmunized. Since documentation is critical, all of us must devise ways of ensuring patient (or parent) retained record of all vaccinations.
 

Need of Rabies Vaccine After a Course of Rabies Vaccination

Q. It is recommended that if there is an animal bite in less than 1 year period after pre-exposure (3 doses) or post-exposure (5-6 doses) rabies vaccination, one dose of rabies vaccine is required on 0 day, and for high degree expo- sure 2 doses on days 0 and 3 are required.

Is there any safe period after the vaccination course when no additional dose of the vaccine would be required after an animal bite? Should We administer rabies vaccine if a bite occurs, say after I month or 6 months of the last dose of the rabies vaccine?

Ans. In general no expert will give categorial recommendations for not giving additional rabies vaccine doses in exposed persons even with previous history of immunization. As in the case described earlier for tetanus prophylaxis, the presence of rabies virus neutralizing antibodies at the time of animal bite or as soon as possible thereafter is what prevents the infection of the nervous system from introduced rabies virus. If antibodies are insufficient, the virus can multiply and cause disease weeks or months or even an year or perhaps more, later.

As cell culture derived rabies vaccines are completely safe and as. I believe that it is no longer ethical to give the animal brain tissue vaccine to humans under any circumstances, I will first give my remarks about those given one or .another cell culture rabies vaccine. Since I do know that brain tissue vaccine is still in use in our unfortunate motherland, I shall deal with persons given that product later. In those given a full course of pre-exposure prophylaxis with 3 doses of any modern vaccine, at least 2 doses (day 0 and 3) of a modem vaccine are suggested during the period of up to a few years and 3 doses (0, 3 and 7 days) if the interval is longer. Although it is difficult to give clear limits of cut off intervals when 2 versus 3 doses might be given, I would suggest that about 5 to 10 years be taken for such distinction. That is, when the gap is less than 5 years give 2 doses and when more than 10 years, give 3 doses. If the gap is in between 5 and 10 years one might decide on either 2 or 3 doses depending upon the severity of bites. It the exposure is severe, with multiple bites or bites on face, head, neck, hands or genitalia, then 3 doses would be safer irrespective of interval.

In those previously given full post-expo- sure immunization (5 doses without and 6 doses with passive immunization), I would suggest the same number of doses as above according to the interval from the last dose, as described above. Here I feel that during the period of several months to perhaps up to one year after the last dose there might be no need to give additional dose, but both the doctor arid the subject might sleep easier with at least one booster dose. After one year it is safer to give 2 doses and after 5-10 years 3 doses.

Perhaps after 20 years or more after the last dose of rabies vaccine according to either the pre- or post-exposure regimen, one might opt for repeating the fu11 course. In all these suggestions the basic principle is to overdo the process of immunization and not to take any chances, even though in most cases such previously vaccinated persons might be already fully protected. The only way to reduce doses or to avoid further doses would be to have either taken a booster dose 5 to 10 years after prior immunization or to have one's antibody level checked and confirmed. The likelihood of either of these is quite unlikely in practice.

No one would have been foolhardy to have taken pre-exposure prophylaxis with sheep brain rabies vaccine. However, some would have taken it before the days of the modem vaccines or even taken it more recently for post-exposure prophylaxis. Those who have had previous immunization with sheep brain rabies vaccine should not be given the same vaccine ever again. They should be given only cell culture vaccine according to the suggestions given above for those previously given cell culture vaccine post-exposure prophylaxis.

As I said earlier these are general guidelines and the principle is to err on the side of over immunization rather than under immunization.
 

Questions by:
Yash Paul
A-D-7, Devi Marg,
Bani Park,
Jaipur - 302 016, India.

Reply:

T. Jacob John,
Chairman,
IAP Committee on Immunization,
Thekkekara,
2/91 E2 Kamalakshipuram,
Vellore - 632 002, Tamil Nadu,
India.

   

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