CONNAUGHT HAEMOPHILUS B CONJUGATE VACCINE EFFICACY IN U.S. INFANTS
CONNAUGHT HAEMOPHILUS B CONJUGATE VACCINE EFFICACY IN U.S. INFANTS should at least match the level seen in Finland, the firm told FDA's Vaccines & Related Biological Products Advisory Committee Jan. 30. Based on data showing higher antibody production levels in U.S. infants compared to Finnish infants, a Connaught representative told the advisory committee: "We conclude that ProHIBIT will be at least as effective in preventing HIB disease in U.S. children as it was in Finland." Connaught was represented at the meeting by Immunobiology Section Head Patrick McVerry, MD. Connaught is seeking an indication for ProHIBIT use in vaccinating infants down to two months of age on the basis of infant efficacy data from Finland and data comparing antibody production levels in Finnish and U.S. infants. The firm reported that as of January, its Finnish study of over 100,000 infants found that the vaccine was 94% effective after three doses and 100% effective after three doses plus a booster. To address the question of extrapolation to the U.S. population, the firm presented data showing that its vaccine produced titer levels over .06 and .15 mcg/ml in a roughly equivalent percentage of U.S. and Finnish infants. "Antibody responses in these two populations are not significantly different and protective efficacy, as estimated from the correlate, are very high," McVerry told the committee. Praxis Biologics and Merck also made presentations to the advisory committee. All three firms are in a race with Connaught to obtain approval for their conjugate vaccines in the infant population. The committee did not make approval recommendations for any of the products. HibTITER, the Praxis vaccine, is currently being tested in U.S. and Finnish infants. HibTITER was approved in December, one year after ProHIBIT, for children as young as 18 months old. The firm currently has a product licensing application pending that includes antibody data on infants. Merck submitted a PLA in the summer of 1988 for its vaccine, PEDVAX-HIB. The firm has not disclosed what age group the filing seeks; however, Merck previously commented that it expects approval of PEDVAX-HIB for children down to 12 months of age in early 1989. The company is conducting clinicals with PEDVAX-HIB in infants down to two months of age in California and St. Louis, and it recently began a trial in 5,000 Navaho Indian children and infants. Although Connaught may be ahead of both Praxis and Merck in terms of infant efficacy studies, several ongoing issues may prove to be obstacles for approval of the labeling extension. The central issue that FDA may have to deal with is whether results of the Finnish infant study can be used to support approval in the U.S. That issue is complicated by the fact that Connaught's vaccine does not produce high antibody titer levels, while the firm's submission is based, in part, on studies comparing antibody production levels in U.S. and Finnish infants. A second issue that complicates approval is results of a trial in Alaska that found no difference in efficacy between the children receiving vaccine and those receiving placebo. The firm presented a number of possible explanations for the finding to the committee, including the fact that a flaw in the randomization procedure may have resulted in children from individual settlements receiving only vaccine or placebo. That fact could have affected results, the firm explained, because of "extreme variation" in the incidence of HIB disease in different settlements. Connaught recently obtained its first approval for marketing ProHIBIT for infants. The Icelandic government approved the vaccine in November and plans to begin innoculating two month old infants in March.
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