BOSTON Because there were so many immunization schedules developed by different organizations and because they were changing so rapidly, a universal immunization schedule was established in 1995. This schedule will be published annually and will provide ranges of ages for different vaccines.
"One major change in the immunization schedule for 1997 is the change from an OPV-based policy to expanded use of IPV. However, this change with polio myelitis vaccine recommendations is only one of the many changes that have occurred in recent years," Georges Peter, MD, said here at a symposium sponsored by North American Vaccine Co. Peter serves on the American Academy of Pediatrics Committee on Infectious Diseases, which produces the Red Book.
According to Peter, the reassessment of polio immunization has been ongoing for at least 20 years. In the late 1970s, a review was commissioned by the Institute of Medicine to look at the continued reliance in the United States on oral polio vaccine (OPV). At that time, OPV was reaffirmed as the vaccine of choice. Then, in the late 1980s, a second review indicated that OPV should remain the vaccine of choice until a combination product was developed that would allow the administration of enhanced inactivated polio vaccine (eIPV) in conjunction with other vaccines.
"During this period, a number of events took place that necessitated reassessment. The first is that we have not had indigenous poliomyelitis in this country since 1979. However, we've had eight to 10 cases of vaccine-associated paralytic polio [VAPP]. Importations have become increasingly rare, and we are making continued progress toward global eradication, which includes the current elimination in the Western Hemisphere of poliomyelitis," explained Peter, who is director of the division of pediatric infectious diseases at Rhode Island Hospital in Providence.
"Children have a greater risk of acquiring vaccine-associated polio than of acquiring natural disease in this country. This doesn't necessarily justify the change to IPV, because we know that OPV has the benefit of enhanced intestinal immunity. IPV also provides the patient some degree of mucosal immunity, but it is not to the same extent, at least as far as the gastrointestinal tract is concerned," he added.
After assessing these findings, three options were considered:
The Centers for Disease Control took the middle road an expanded use of IPV. "However, this recommendation does not undermine the support for global eradication with OPV for that purpose," Peter said.
The Advisory Committee on Immunization Practices (ACIP) has recommended using a sequential IPV-OPV schedule as a transition until the time when IPV only could be given.
However, there are some problems associated with changing to an IPV-only schedule. Extra injections will be required until a combination product is available. Costs will be greatly in creased: it will cost $14 million per year per case of VAPP prevented for the sequential schedule and $28 million per year for IPV only. Another potential problem is decreased intestinal immunity.
According to Peter, other important developments include: the approval of varicella and hepatitis A vaccines; the addition of acellular pertussis to the primary series; including teens in the universal hepatitis B schedule; and the development of combination vaccines.
The National Vaccine Injury Act of 1986 is also an important development. "I think it is a watershed event in the history of immunizations in this country, because that particular act established the compensation program. This program was developed at a time when the future of vaccines as a commercial enterprise was threatened in this country because of rising prices, increased litigation and a paucity of manufacturers in the market. Today, prices have been stabilized as a result of the vaccine compensation program, physicians no longer worry as much about litigation, and the pharmaceutical firms realize that they now have some protection from frivolous suits. It creates a climate in which new vaccines can be developed, and it creates an economic marketplace that allows new companies to enter into the development of vaccines," explained Peter.
"In the future, we may see development of new vaccines for the adolescent immunization visit. Also, hepatitis A vaccination of in fants is a possibility once we have the appropriate combination product," Peter said.
"Some of the vaccines that are still under development include vaccines for group B Streptococcus Lyme disease, respiratory syncytial virus, cytomegalovirus, herpes simplex and HIV," he added.
Another interesting concept is the use of plants for the delivery of vaccines. "If this is successful, we just have to get children to eat their bananas in the morning, and they will be immunized. Physicians no longer would have to give vaccines, but I don't think it's going to happen within the next few years. The concept is that one could splice the gene from a given bacteria that's responsible for the production of a vaccine antigen into a plant. One can incorporate as many as 10 different antigens; and, through digestion, one would have both mucosal immunity and systemic immunity. It's an exciting concept," Peter explained.
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