PASTEUR MERIEUX' HAEMOPHILUS B VACCINE ActHIB IS SAFE AND IMMUNOGENIC, ADVISORY CMTE. CONCLUDES; ActHIB SHOULD NOT BE RECONSTITUTED WITH DTP VACCINE

Pasteur Merieux' Haemophilus b vaccine ActHIB is safe and immunogenic, FDA's Vaccines and Related Biological Products Advisory Committee unanimously agreed at its Oct. 28 meeting. Committee member Catherine Wilfert, MD, Duke University Medical Center, stated: "I'm actually impressed with the consistency of all the information." She added that "the immunological markers that we're using seem to be so consistent ...and the hints at efficacy based on rather large trials started to bear that out." Bernard Fritzell, MD, Director of Clinical Research at Connaught Labs, Pasteur Merieux' U.S. affiliate, presented immunogenicity data from three randomized studies that compared the conjugate vaccine ActHIB with other Haemophilus b vaccines. Fritzell said the studies show that ActHIB produces "an equivalent or better PRP-T antibody response" after three doses at 2, 4 and 6 months of age than two other Haemophilus vaccines, Lederle-Praxis' HibTITER and Merck's PedvaxHIB. ActHIB would be the fourth Haemophilus b conjugate vaccine to enter the U.S. market. Based upon previous agreement with FDA, Pasteur conducted immunogenicity studies instead of efficacy trials because of the difficulty of doing large efficacy trials given that other Haemophilus vaccines are on the market and Haemophilus b disease largely has been eliminated in the U.S. Efficacy trials of ActHIB in the U.S. were stopped when HibTITER was approved for use in infants in 1990. At its Sept. 5, 1991 meeting, the advisory committee determined that antibody titer data was acceptable in lieu of Phase III studies to measure efficacy against Haemophilus b ("The Pink Sheet" Sept. 9, 1991, T&G-6). Although the committee agreed that ActHIB should be licensed, it did not endorse proposed labeling concerning the vaccine's reconstitution with Connaught's DTP vaccine. The proposed labeling directed physicians to reconstitute lyophilized ActHIB with diphtheria, tetanus toxoids adsorbed and pertussis (DTP) vaccine manufactured by Connaught. The labeling also provides for ActHIB to be reconstituted with saline diluent. The committee concluded that there was insufficient data to demonstrate that there is no immunological interference between vaccine components in the combination. Fritzell presented three studies that compared the antibody responses produced by ActHIB and Connaught's DTP given separately to the responses from the vaccines given in combination in a total of 270 children. "All of the three studies have shown that PRP-T reconstituted with Connaught's DTP is safe and that the immunogenicity profile is generally similar to the DTP and PRP-T given separately," Fritzell said. However, the committee expressed concern with the number of children and number of lots involved in the combination studies in light of a study of ActHIB combined with Pasteur Merieux' formulation of DTP that was reported in the Feb. 5, 1992 issue of Journal of the American Medical Association by Clemens et al. The study found that Chilean children given ActHIB combined with Pasteur's DTP vaccine or given ActHIB or the DTP vaccine separately had lower pertussis agglutinin titers than children given DTP only. Fritzell said that "contrary to what has been reported in one controlled study with the Pasteur Merieux prepared formulation of DTP, PRP-T given as a reconstitute with the Connaught DTP or [separately] does not interfere with antibody response to each component of the DTP, including pertussis." Following the meeting, Pasteur Merieux/Connaught said that it will consider conducting more studies to get approval for labeling directions that provide for combining the ActHIB and DTP vaccines. Patricia Ferrieri, University of Minnesota, who was a temporary committee member, said: "I think the data as presented suggests safety of the reconstitution...but I think the data are insufficient and I would recommend to FDA to ensure that these numbers are expanded and we need further assurance that there is no abrogation of the immunological response to the components of the DTP."