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Immunization Dialogue Indian Pediatrics 2001; 38: 201-203 The views expressed by Prof. T. Jacob John in this section are personal in nature and should not be construed as the official stand of the Indian Academy of Pediatrics. –Editor-in-Chief |
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Technical Differences Between Vaccines: Convincing or Confusing |
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Ashok Banga, The problem raised by Drs. Ashok and Usha Banga is not confined to vaccines alone, but also to all newly introduced pharmaceuti-cals such as drugs and drug combinations. Each branded product, proprietary prepara-tion or vaccine produced by any company is bound to have some differences from similar products already in the market. Such differences may or may not represent some improvement of the new product. The marketing strategy of some companies may tend to highlight the difference as a new property and imply that the new property makes that vaccine better than its competitors. As mentioned in the question, such arguments may confuse doctors even if they do not convince them. Here the real problem is that many doctors rely on company representa-tives for updating knowledge without verifying if such newly obtained information is in agreement with peer-reviewed publica-tion in journals. As far as vaccines are concerned, the Immunization Committee has a responsibility to help in updating the knowledge of IAP members. During the past several years, the Indian Pediatrics has served as a user-friendly medium to answer the innumerable questions raised by members of IAP. Regarding Haemophilus influenzae b vaccine, there are several products in the market and the choice among them can be confusing to anybody. There are essentially 4 conjugate Hib (PRP) vaccines using D (diphtheria toxoid), CRM197 (nontoxic mutant of diphtheria toxin), TT (tetanus toxoid) or OMP (Meningococcal outer membrane protein) as the protein moiety. None of them is adjuvanted with aluminium salt. The USA Food and Drugs Administration has approved the PRP-D only for children of 12 months and above. During infancy any of the remaining 3 vaccines are approved; however, if PRP-OMP is used, only 2 doses are sufficient for primary immunization as against 3 doses of PRP-T or PRP-CRM. The booster at 1 year may be with any of the 4 vaccines. Recently, one Hib vaccine with aluminium adjuvant has been approved in India. Due to its enhanced immunogenicity, it may be sufficient to give 2 doses for primary immunization, but this has to be proven to be valid by investigation. If 3 doses are given, there may not be the need for booster. Indeed it remains to be proven if our children do or do not need a booster after receiving 3 doses in infancy, irrespective of which specific vaccine had been given. If one wants to avoid aluminium, then the adjuvanted vaccine should not be used. There has not been any problem with aluminium adjuvants in DPT and related vaccines or in hepatitis B vaccines. One may argue that there should not be any problem with one more aluminium adjuvanted vaccine. Another may argue that we already have several doses of adjuvanted vaccines to be given in infancy; therefore another vaccine with aluminium may be avoided unless shown to be essential. To the best of my knowledge, there is no data to show which of these choices is better. Regarding the genetically engineered hepatitis B vaccines, in India we have two different products, one produced using Saccharomyces cereviseae as the substrate (or vector) and the other using Piccia pastoris as the substrate. The end product (HbsAg as vaccine) is identical and we cannot use the information as to which substrate was used, to make a choice between the two vaccines. However, the yield is said to be superior in the Piccia yeasts and there is a claim that this vaccine is more immunogenic than the one produced in Saccharomyces yeasts. It is more likely that the immunogenicity may not be related to the yeast vector, but rather, due to the quantity of antigen in the vaccine, or perhaps the degree of distortion of the antigenic epitopes during purification. Another recent issue regarding HB vaccines is the presence of pre-S peptides in some vaccines. There is insufficient informa-tion as to the consequences of the presence or absence of the pre-S peptides in HB vaccine. The majority of recombinant HB vaccines produced by various companies do not contain the pre-S peptides and they have proved to be of excellent efficacy in terms of immunogenicity as well as protection. Can IAP function as an agency that receives all relevant information from all vaccine manufacturers and makes pronounce-ments on them? From a legal point of view this is not tenable. Once the Drugs Controller approves a vaccine for sale in the country, the marketing agency obtains the right to promote it. What we have been doing so far is to critically assess the pluses and minuses, if any, of the approved vaccines and to provide clear technical guidelines on the correct use of such vaccines. If any issue is not clear, the Immunization Dialogue is available for clarification. That I feel is the right thing for IAP to do, rather than taking on more of a policing or censuring posture.
T. Jacob John, |
