Evaluation of the new generation of conjugate vaccines is hampered by the absence of reliable surrogate markers of immunologic memory. Memory responses are characterized by rapid production of relatively high-avidity antibody; thus, a solid-phase ELISA was adapted for the measurement of anti- Haemophilus influenzae type b (Hib) IgG avidity. In a cohort of infants vaccinated at 2, 3, and 4 months of age with Hib conjugate vaccines, avidity increased in the period following vaccination, while antibody titer fell. After a booster dose at I year of age, both antibody titer and avidity increased. In a cohort with anti-Hib IgG < 1.0 μg/mL following primary immunization, antibody avidity after booster was low, indicating an absence of priming. Antibody avidity may help distinguish, in persons with low antibody titers, between those who are primed for memory and those who are not.
Bibliographical noteFunding Information:
Received 27 June 1997; revised 21 October 1997. Presented in part: 37th Interscience Conference on Antimicrobial Agents and Chemotherapy, Toronto, September 1997 (abstract G-103). Written informed consent was obtained from the parents or guardians of all study participants, and the study protocol was approved by the ethics committees of the Gloucestershire and East and North Hertfordshire Health Authorities. Financial support: Medical Research Council (grant G9431974). D.G. is funded by the Wellcome Trust. Reprints or correspondence: Dr. D. Goldblatt, Immunobiology Unit, Institute of Child Health, 30 Guilford St., London WC1N 1EH, UK (d.goldblatt@ ich.ucl.ac.uk).