On an average I am giving BCG to 50 babies every month. However, inspite of taking the best care regarding inoculation procedure, I am getting 10% failure of BCG vaccine take up. I am treating it as a failed BCG vaccination, if no scar is seen even after 90 days of inoculation. I do revaccination and am getting 90% positive results in the revaccinated babies. In this context, I seek the following clarifications:

1. Is it correct to assume a "failed" BCG vaccination if no BCG scar is seen even after 90 days of inoculation?

2. Is the rate of 10% failure of BCG ‘take up’ acceptable?

3. Why am I getting 90% positive results in the revaccinated babies?

4. Is it essential to give BCG vaccination to every child who is not having BCG scar, even when the mother is sure that BCG was given to the child at the age of 1 month or so?

5. Is it mandatory to perform a Mantoux test in all children above 1 year of age who do not have BCG scar and whom I want to revaccinate with BCG?

Sudhakar Joshi,
D4, Panchavati CHS, Marol,Andheri (E),
 Mumbai 400 059, India.

Reply

Dr. Sudhakar Joshi deserves our appreciation for his personal observations on BCG vaccination and also for the clear and succinct questions he has asked. Let me answer them sequentially.

1. While it is correct to ‘assume’ failed BCG vaccination if no scar is seen 90 days after inoculation, it does not necessarily mean that it had actually failed to induce some immune response that can be proved by laboratory tests. Since it is clinically impossible to distinguish between failed vaccination and failure to develop scar in spite of immune response, the better clinical option is to inoculate BCG a second time. This issue had been discussed in several earlier pieces in Indian Pediatrics, as article, Letter to the Editor and Immunization Dialogue.

2. A failure (of ‘take’ with scar formation) rate of 10% is equal to a success rate of 90%, which is quite respectable and acceptable. This rate tells us that the vaccine is satisfactory and the inoculation technique is good.

3. Dr. Joshi’s observation of 90% success in the previoulsy failed cases needs some attention. I assume that the evolution of the local lesion and scar formation in them were more like primary BCG vaccination and not like the accelerated reaction of revaccination, or the so-called positive ‘BCG test’. In other words, I assume that they behaved as if they had no previous experience with BCG. If my assumption is correct, it shows that the failure was: (a) indicative of true failure and not merely lack of scar in spite of immune response; and (b) a random phenomenon and not due to factors of the host or agent. Perhaps it could be related to some unrecognized fault of inoculation technique, but such an explanation is unlikely since the success rate is high both in primary inoculation and in second inoculation of failed cases.

4. The answer to the question is already available in Dr. Joshi’s experience. Obviously, babies are responding normally to the second inoculation, which proves that it is the right strategy. Had these infants been immune, they would have exhibited accelerated response (and as stated earlier I assume that was not the case). The problem is not with these 99%, but the remaining 1% who had no ‘take’ or scar in spite of two attempts. There are the two possibilities once again, namely, no immune response or no scar in spite of immune response. My opinion is that we must assume that the former is the case; in other words, ideally a third attempt must be made when once again the response rate could be 90%. Mathematically also the chance of success would seem to be 90% for each attempt, for sequential cumulative response with each additional dose of 90%, 99% and 99.9%. With the third attempt I would stop even if there was no ‘take’, assuming immune respone without scar. Now, had the success rate been 99% the first time, and 99.9% with the second inoculation, I would not go for a third attempt. I am a believer in our own experience as our guide, provided we interpret our results thoughtfully.

5. No, it is not mandatory to do Mantoux test before reinoculation of BCG in preschoolers who have a history of BCG inoculation, but no scar. There would be no harm in giving them BCG again and you will see ‘take’ in some, accelerated response in others and no response in a few. Scientifically speaking, it would be ideal to test them with PPD and to classify them as those with no response (meaning no prior immune response), with positive response but induration of 5 to 10 mm (most probably immune response due to earlier BCG) or induration of 15 mm or more (most probably infected with Myco-bacterium tuberculosis). The first group deserves a second attempt with BCG. It will be difficult to interpret indurations of 3 to 4 mm and my bias would be to treat them as immune due to BCG. It will be more difficult to interpret induration of 11 to 14 mm as to whether it is due to BCG or M. tuberculosis, but my bias would be to assume that it is due to M. tuberculosis infection, particularly since there is no BCG scar. Those children with M. tuberculosis infection (15 mm or more induration certainly, and perhaps those with 11 to 14 mm also) should, in my opinion, be given INH ‘chemoprophylaxis’. I understand that out in the real world, not much attention is being paid to these issues, and I think we are making a mistake by not taking these issues very seriously. Without such careful handling of infected children, tuberculosis control by the current tactics of addressing exclusively the adult open pulmonary disease will not, in my personal opinion succeed in achieving the goal.

T. Jacob John,
Chairman, IAP Committee on Immunizatin,
Indian Academy of Pediatrics,
2/91 E2, Kamalakshipuram,
Vellore 632 002, TN, India.