CONNAUGHT ProHIBIT HAEMOPHILUS b: NO CONSENSUS ON INFANT USE
CONNAUGHT ProHIBIT HAEMOPHILUS b: NO CONSENSUS ON INFANT USE was reached at the Jan. 25 meeting of the FDA Vaccines and Related Biological Products Advisory Committee. Members of the committee disagreed on whether existing data would support approval for use in children down to four months of age. The product is currently indicated for children 18 months and older. A formal vote was not taken on the issue. FDA asked the committee to determine whether encouraging results from two large trials with ProHIBIT in Finland and poor results from a study in Alaska would provide adequate support for the proposed labeling change. ProHIBIT was first approved in December 1987 for use in children 18 months old to five years of age. The approval was based on the results of a two-year trial of ProHIBIT in Finland in more than 100,000 children that showed an overall efficacy of 94%. In support of an infant indication, Connaught sponsored a second large-scale trial of its vaccine in Finland. The two-year study, completed in October 1989, enrolled more than 100,000 infants, half of whom received ProHIBIT or Praxis Biologics' Haemophilus b conjugate vaccine HibTITER at four, six and 14 months. To determine efficacy in the second Finnish study, Connaught used the control group from the first Finnish trial. Connaught VP-R&D Howard Six, PhD, presented the results: "At six to 14 months of age, there have been four cases [of Haemophilus b] in the PRP-D [ProHIBIT] vaccine group. During a comparable period of time...28 cases would have been expected in the control group and that calculates to an efficacy of 86%." Six noted that they are evaluating whether illness in a fifth child, who received the first dose of ProHIBIT at nine and one-half months, should be included in results as a case of Haemophlius b. Praxis asked Juhani Eskola, MD, head of the Infectious Disease Unit, National Public Health Institute in Finland, to present the results of a head-to-head comparison of HibTITER versus ProHIBIT from the second Finnish trial. Eskola reported that, following the administration of both products, there were no cases of Haemophilus b occurring with HibTITER, while five cases occurred with ProHIBIT, including the case still under review by Connaught. Eskola noted that the difference in the outcome with the vaccines was statistically significant. The placebo-controlled study of PRP-D vaccine involving over 2,000 native Alaskan infants found that the vaccine was 25% effective after one dose at two months, and 43% effective after the third dose at six months. In casting his recommendation for approval, panel member John Mekalanos, MD, Harvard Medical School, said that the data "makes it very clear that both of these vaccines work quite well to prevent this disease in the Finnish population," [but] "it's very difficult for me to ignore the data from the Alaskan trial." He pointed out that "the Alaskan situation probably more closely mimics what would occur in North America than what [happens in] the Finnish situation." Mekalanos added that "we can probably prevent a lot of disease and save lives by licensing the Connaught product...we can probably protect even more lives or at least prevent more disease with the Praxis product." He concluded: "I have to go with saving lives immediately...I would recommend that it be licensed." Praxis currently is conducting a large-scale controlled study of HibTITER's use in infants in California. The study has enrolled 48,000 infants, 22,000 of whom are getting HibTITER at two, four, and six months with a booster at 18 months. Praxis said it expects to submit the data to FDA "early this year." HibTITER and Merck's Haemophilus b vaccine PedvaxHIB are currently indicated for children 18 months and older. PedvaxHIB is now being studied for use in the younger age group in a large trial of Navajo Indian children and infants.
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