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Advisory Committee on Immunization Practices Update: Report of PedvaxHIB Lots with Questionable Immunogenicity

Since 1988, the rate of Haemophilus influenzae type b (Hib) disease has decreased in the United States primarily because of the introduction and use of three Hib conjugate vaccines in infants and children. In CDC-coordinated active surveillance areas, rates of reported Hib disease among children aged less than 5 years have decreased by 95% from the first half of 1989 to the first half of 1992 (CDC, unpublished data, 1992). Other population-based studies with each of the two vaccines licensed for infants also have shown decreases in disease incidence in all age groups (1-3).

One of these vaccines, PedvaxHIB * (Haemophilus b conjugate vaccine [Meningococcal Protein Conjugate], MSD, Merck and Co., Inc., West Point, Pennsylvania) has been distributed in the United States since 1989 and has been recommended for use in infants since December 1990. The manufacturer is notifying physicians that data obtained after licensure indicate that 16 lots ** of this vaccine may have lower than expected immunogenicity. The lots were initially distributed from August 1990 through August 1991 and had expiration dates from April 1991 through May 1992. These 16 lots comprise 366,000 doses of a total of approximately 2 million doses of PedvaxHIB distributed, or about 1% of all Hib conjugate vaccine released in the United States since January 1990. Although vaccine from these lots induced a lower antibody response, the precise level of antibody necessary for protection is not known, and there is no clear evidence that children receiving vaccine from these lots are at increased risk for disease. Given the limited period of distribution of these vaccine lots, it is unlikely that many children received all three recommended doses (at 2, 4, and 12-15 months of age) from lots with reduced immunogenicity. In addition, most children who have received vaccine from these lots will now be greater than 18 months of age and at lower risk for Hib disease. The company will contact physicians who received vaccine from these lots and has suggested that selected recipients of these lots receive an additional dose of Hib conjugate vaccine. Inquiries about use of vaccine from these lots may be directed to Merck and Co., Inc. ([215] 652-7300, collect).

All current lots of PedvaxHIB that have been tested have expected immunogen- icity. In view of the success of the Hib conjugate vaccines in preventing Hib disease, the Advisory Committee on Immunization Practices recommends that physicians should ensure all children are up-to-date with the recommended Hib conjugate vaccine schedule. To facilitate postmarketing evaluation of Hib conjugate vaccines, physicians are encouraged to record lot numbers and manufacturers of vaccines administered for all children, and to report any case of invasive Hib disease in a child less than 5 years of age to local and state health departments.


  1. Black SB, Shinefield HR, the Kaiser Permanente Pediatric Vaccine Study Group. Immunization with oligosaccharide conjugate Haemophilus influenzae type b (HbOC) vaccine on a large health maintenance organization population: extended follow-up and impact on Haemophilus influenzae disease epidemiology. Pediatr Infect Dis J 1992;11:610-3.

  2. Santosham M, Wolff M, Reid R, et al. The efficacy in Navajo infants of a conjugate vaccine consisting of Haemophilus influenzae type b polysaccharide and Neisseria meningitidis outer-membrane protein complex. N Engl J Med 1991;324:1767-72.

  3. Vadheim CM, Greenberg DP, Eriksen E, et al. Reduction of Hib disease in southern California, 1983-1991. In: Program and abstracts of the 32nd Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1992;398.

    • Use of trade names and commercial sources is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services. ** Lot numbers of PedvaxHIB with questionable immunogenicity are 1160S, 1724S, 1726S, 2377S, 2379S, 0485T, 2378S, 2380S, 0405T, 0853T, 0172T, 0173T, 0498T, 0774T, 0884T, and 1288T.

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