Follow-up of Saudi children vaccinated with Haemophilus influenzae type B vaccine

Saudi children vaccinated with a primary series of Hib vaccine (HbOC) at six weeks, three and five months have shown higher antibody titers compared to recent data from the U.S. The aim of this study was to evaluate the persistence of antibodies and to measure the immunogenicity of a booster dose of Haemophilus influenzae type b (Hib) vaccine in Saudi children.

In the first phase of the trial, 210 children were divided into three groups. Group 1 received HbOC, DPT and the WHO formula of oral poliovirus vaccine (OPV); group 2 received HbOC, DPT and the FDA formula of OPV; and group 3 (control) received DPT and the WHO formula of OPV, without HbOC. Haemophilus influenzae geometric mean antibody levels after primary immunization were reported previously. In this study, blood samples were collected at 18 months (before the booster dose) and one month later to measure antibody levels against Haemophilus influenzae polysaccharide.

Following the booster doses, there was an increase in the geometric mean titers (GMTs) from 2.57 microg/mL to 39.4 microg/mL in group 1, and from 1.2 microg/mL to 48.9 microg/mL in group 2. In group 3, the GMT remained at 0.3 microg/mL. There was no significant difference in Hib GMTs after the booster dose between children given Hib vaccine with the FDA formula of DPT and OPV and those given the WHO formula.

Based on the high immunogenicity of the Hib vaccine in Saudi children, a booster dose is not necessary at the initial stages of immunization, and should instead be given to children in the second year of life. This option, however, needs further evaluation and close monitoring.