Functional antibody activity elicited by fractional doses of Haemophilus influenzae type b conjugate vaccine (polyribosylribitol phosphate-tetanus toxoid conjugate).

We evaluated the functional activities of antibodies, serum bactericidal activity (SBA), and immunoglobulin G (IgG) antibody avidity indices, using sodium thiocyanate (NaSCN) elution, elicited after vaccination with fractional doses of the Haemophilus influenzae type b conjugate (polyribosylribitol phosphate [PRP] conjugated to tetanus toxoid [PRP-T]) vaccine. A cohort of 600 infants from the Dominican Republic were randomized to receive one of three regimens of the PRP-T vaccine at ages 2, 4, and 6 months: full doses (10 microg of PRP antigen), one-half doses (5.0 microg), and one-third doses (3.3 microg) (J. Fernandez et al., Am. J. Trop. Med. Hyg. 62:485-490, 2000). Sixty serum samples, collected at age 7 months, with > or =2.0 microg of anti-PRP IgG per ml were randomly selected for avidity determinations. Geometric mean IgG concentrations were 13, 14, and 17 microg/ml for infants who received the full-dose (n = 19), one-half-dose (n = 19), and one-third-dose (n = 22) regimens, respectively. SBA geometric mean titers (1/dilution) were 85.0, 82.0, and 76.1 in sera from infants receiving the full-, one-half-, and one-third-dose regimens, respectively. Avidity indices (mean +/- standard error weighted average of NaSCN molar concentration x serum dilution factor) were 71.9 +/- 9.4, 123.6 +/- 26.8, and 150.9 +/- 24.9 for the full-, one-half-, and one-third-dose regimens, respectively. Upon comparison, the only significant difference (P = 0.024) found was a greater avidity index for sera from infants receiving the one-third-dose regimen than for sera from infants receiving the the full-dose regimen. We conclude that fractional doses elicit similar functional antibody activities in infants with > or = 2 microg of anti-PRP IgG per ml, corresponding to 89, 90, and 97% of infants receiving three doses of either the full concentration or one-half or one-third of the labeled concentration, respectively. This approach offers an alternative strategy for the prevention of H. influenzae type b disease in countries with limited resources.

Overview of meteorological measurements for aerial spray modeling.

The routine meteorological observations made by the National Weather Service have a spatial resolution on the order of 1,000 km, whereas the resolution needed to conduct or model aerial spray applications is on the order of 1-10 km. Routinely available observations also do not include the detailed information on the turbulence and thermal structure of the boundary layer that is needed to predict the transport, dispersion, and deposition of aerial spray releases. This paper provides an overview of the information needed to develop the meteorological inputs for an aerial spray model such as the FSCBG and discusses the different types of instruments that are available to make the necessary measurements.