Should Typhoid Vaccine be given to a child who has recently recovered from enteric fever? If so, when it should be given and which vaccine is most beneficial?
 

S.K. Joshi,
Pediatrician,
KAPS Hospital, Anumala, Surat, India
 

Reply

The purpose of giving typhoid vaccine is to prevent typhoid fever. Therefore, if a child developed the illness without the benefit of protection from the vaccine, the very purpose of immunization was lost on that child. In other words, the priority of typhoid vaccine is for children (and adults) who are at some risk on account of the prevalence of typhoid fever in the community in which they live or travel to. Obviously, we will not be able to know when and in which child the illness would have occurred in the absence of protection and which was prevented by prior immunization. For documenting protection we need to measure the incidence of illness in the unvaccinated and in the vaccinated groups of children and then we can calculate the proportion of prevented disease. That is the measure, of vaccine efficacy.

In the case of specific viral illnesses such as measles or acute hepatitis B (with recovery from infection), after one attack of illness immunization is no longer recommended. That is because one attack provides long, indeed life long, protection against another attack of the same illness on account of immunity. In the case of many bacterial diseases such as typhoid fever, one attack does not provide solid or long lasting immunity from a future episode of the same illness. Although second attack is recognized anecdotally, I am not aware of any systematic study in which the frequency of such repeat illness has been measured in a community endemic for typhoid fever. Implicit in this statement is the fact that one episode does provide some immunity and the incidence of typhoid fever as second episodes must indeed be very low. There is also the possibility that early treatment would have reduced the full force of immunity from developing. The child with typhoid fever is likely to be going back to the same environment with continuing risk of infection. Taking all these into consideration, the classical teaching is to give typhoid vaccine to such a person, but after full recovery from the illness.

In olden days, only the killed whole cell vaccine was available. Some physicians treated typhoid fever with chloramphenicol and concurrent typhoid vaccination. This is no longer considered necessary or appropriate. But vaccination after recovery is often taught as a good practice. I have no data as to how often this is followed in actual practice in different places. Again, I have not come across any specific study investigating the benefits from giving vaccine after recovery from typhoid fever. So the whole issue is on theoretical basis. Since the disseminated infection with Salmonella typhi would have induced immune responses to the 0 and H antigens, I feel that one dose of whole cell killed vaccine should be sufficient to raise the immunity levels. Subsequently, booster doses may be given once in 3 years to begin with, the latter once in 5 years. I suppose that a dose of Vi vaccine might also suffice although there is no information on the response of children to this vaccine given in this situation. I would not expect a booster type response, but I will also not rule out such a possibility until proven one way or another. My 'gut feeling' is that the oral vaccine may not add anything more to the gut immunity already induced by the pro- longed infection by the virulent S. typhi during the incubation period, the illness and convalescence. Let me once again emphasize that all these are on theoretical grounds and if any one has relevant data to support or refute any of these points, I will appreciate hearing from them. To the pointed question as to which vaccine is most beneficial, I must say that my bias is towards the whole cell killed vaccine be- cause it continues the immune processes be- gun by the infection itself.
 

T. Jacob John,
Chairman, Immunization Committee and President,
Indian Academy of Pediatrics,
Thekkekara, 2/91, Erkamalakshipuram.
Vellore 632 002, India.