ACELLULAR PERTUSSIS VACCINE EFFICACY IN INFANTS MAY BE "ASSUMED" BASED ON JAPANESE DATA: ACTUAL RESULTS DO NOT WARRANT U.S. LICENSURE, WORKSHOP INDICATES
Japanese clinical trials of acellular pertussis vaccine do not provide specific efficacy and reactivity data on use of the vaccine in infants, participants at a Sept. 22-24 FDA workshop indicated. However, the workshop participants acknowledged that the data may permit assumptions of efficacy. Workshop panelist E. A. Mortimer, Case Western Reverse University, stated that Japanese researchers have developed acellular vaccines that exhibit clinical efficacy in children two years of age and older and that have less frequent local, systemic reactions. However, he said the data from Japan is "not sufficient to warrant licensure in the U.S. for several reasons." First, Mortimer stated, "efficacy and reactivity in infants haven't been determined and with good reason we believe that this age group must be studied." Panelist June Osborn, University of Michigan School of Public Health, commented that the mortality and complication rate for pertussis is "inversely related to age." Mortimer said another reason Japanese experience does not warrant U.S. licensure is that the protective antibody or antibodies "have not been determined with precision." However, he added that "we'll probably learn that our acellular vaccines are effective in infancy. We may learn something about the relative importance of LPF [lymphocytosis promoting factor] and FHA [filamentous hemagglutin antigens], although it appears unlikely that the precise level of antibody that correlates with clinical protection will be established." Mortimer concluded: "Very simply, whether licensure occurs at this point . . . depends on the assumptions we are willing to make." He said "one assumption might be that if [the vaccine is] protective in two-year olds, it should be protective in three-, four-, six-month old kids." Osborn commented that researchers "will be pressed into action at a stage somewhat earlier than we otherwise might like insofar as current data are concerned." She stated that not very much is known about the rate complications that will be associated with the acellular vaccine. "There will probably never be a bacterial vaccine completely lacking in a rare complication," Osborn observed. Data on the Wyeth-Takeda acellular vaccine was presented at the workshop. Edwin Anderson, Marshall University School of Medicine, reported the results of a study of 39 infants aged two to six months, 20 of which received the whole cell DTP vaccine and 19 of which received the acellular vaccine. Anderson said that "seriological results in infants receiving the standard DTP were similar to those in infants receiving acellular DTP," except after the third immunization "the infants receiving the whole cell DTP had a significantly higher agglutination titer to pertussis." With regard to adverse effects, he said increased temperature and greater swelling were more common among those receiving standard DTP compared to those receiving the acellular vaccine during the first and second immunization, but on the third immunization there were no significant differences in adverse reactions. Wyeth said it is no longer pursuing the acellular vaccine, but is completing clinicals. Wyeth no longer markets a whole cell vaccine; it is manufacturing that vaccine for Lederle under contract until the end of the year. Lederle filed an IND for its acellular pertussis vaccine this past summer. The firm is not currently studying the vaccine in infants. Commenting on current acellular research, panelist William Jordan, National Institute of Allergy & Infectious Diseases, stated that future research could tell us such things as the correlates of immunity; how to standardize antibody assays; what the role of adults is in transmission; and what the ideal ratio of components is in an acellular vaccine. He noted that the ratio of components varies widely among Japanese vaccines, "yet each of these vaccines . . . seems to work."
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