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Immunization Dialogue Indian Pediatrics 1999;36:1274-1275 |
Integrating BCG and HBV into the Immunization Schedule |
| One sometimes comes across a baby who has received OPV at birth, HBV 1 on Day 5, BCG at 2 weeks of age, HBV 2 at around 1 month, and DPT-OPV at 1� months. The "reason" for this is that HBV is given only once a week, from a multidose vial; and BCG is available only once a month. How may a Pediatrician in the Private Sector integrate BCG and HBV into the immunization schedule? Should one prefer single-dose ampoules of HBV so that OPV and HBV can be given together soon after birth? Is HBV effective in preventing perinatal transmission if it is given a week after birth? Do live vaccines interfere with the take of killed vaccines and vice versa if the interval between them is less than one month? R. Parvathy, Reply Now that we have several more vaccines than the 4 original EPI vaccines (BCG, OPV, DPT, Measles), integrating them into a user-friendly and technically correct immunization schedule becomes increasingly difficult, as Dr. Parvathy points out. A schedule has several components, such as the choice of vaccines, the number of doses of each vaccine and the guidelines on the age at which each dose is due. The age of recommended doses is defined taking into consideration, mainly, the epidemiological need at that age, the immunogenicity of the vaccine at the given age, and, the likelihood of the presence of maternal antibodies and their inhibitory effect on vaccine response. Dr. Parvathy illustrates with a baby who got OPV at birth, HBV 1 on day 5, BCG at 2 weeks of age, HBV 2 at about 1 month, and DPT-OPV at 1.5 months, and, although not explicitly stated, implies that this sequence of immu-nizations has not been satisfactory. And, why not? From an immunological point of view, this sequence is satisfactory. These intervals do not affect the immunogenicity of any of these vaccines. The main issue here is that these 5 separate contacts for immunization could easily have been condensed to just two, the first for HBV, OPV and BCG and the second for HBV 2, OPV 2 and DPT 1. There are advantages and disadvantages for either approach. If parents do not wish more than one injection per session, then the second approach will not suit them. Eventually, combination vaccines (DPT+HBV; DPT+IPV+HBV, etc.) will help us resolve this issue to some extent at least. Although not specifically asked, there seems to exist an assumption that the multidose vial of HBV is to be used up in one day. "HBV is given only once a week, from a multidose vial" is what Dr. Parvathy has stated. Let me make it very clear, that, we can use the multidose vial of HBV like any other multidose phar-maceutical or biological which is in liquid form (but not if it is lyophilized and reconstituted). In other words, the injection of HBV need not be restricted to limited days simply because the vaccine is in multidose vials. If due precautions of antisepsis are practiced and if the vaccine vial is not left outside the cold chain for unduly long periods, then the multidose vial can be entered on more than one day. Among the three `at birth' vaccines, the greatest urgency is for HBV to be given as soon as possible after birth, and preferably within 12 hours. Giving BCG and OPV at birth are more for convenience than for immediate need for protection. So, we can accept the once-a-month approach to BCG, but not the once-a week approach to HBV. The prevention of perinatal HB virus transmission (vertical transmission) requires, ideally, HB immunoglobulin and active immunization, if the mother is a virus carrier. If vaccine alone is started within 12 hours, and the second dose given about 4 weeks later, still we can achieve some 95% probability of protection from vertical transmission. Note, that we use the term transmission while we actually mean infection. Immunization, passive plus active or active alone protects from infection taking root, in spite of `exposure', or transmission of the virus. This is akin to post-exposure prophylaxis as in cases of dog-bite (rabies) or penetrating injury (tetanus). Here, timing is very important; earlier, the better. If there is delay, the probability of protection is reduced. I cannot categorically give a cut-off interval beyond which protection is unlikely, but I would feel that there is little or no likelihood of protection if the first dose is delayed beyond just a few days. By 7 days after birth, probably there would be very little, if any, chance of protection from vertical infection. The last question relates to possible interference between replicating (live) and nonreplicating (killed, inactivated, subunit, etc.) antigens in various vaccines. In general, no, there is no such interference, no matter what the intervals between these various antigens. When Measles vaccine (and MMR) is given, it is prudent to give an interval of 4 weeks before another vaccine, particularly a live vaccine (except for OPV) is given. Otherwise, injected vaccines can be conveniently spaced so that too many simultaneous injections are avoided. While making the schedule we might say that a dose of DPT, HBV and Hib may be given at one sitting; but if the doctor or the parents so wish, they can be spaced conveniently, giving preference to the vaccine that is required to produce immunity earlier. For example, if HBV had been given at birth, the next priority is for the second dose of HBV (4-6 weeks after the first dose) and for Hib (first dose at 6 weeks of age or at 2 months, if it had been decided to give). DPT can wait a bit, if necessary. OPV, being orally given, can be given convenient- ly along with any other injectable vaccine dose. T. Jacob John, |
