Measure antibody persistence prior to booster administration of Pentabio vaccine.

Number and percentage of children with anti diphtheria, titer and anti tetanus titer >= 0.01 IU/ml, anti HBs >=10mIU/ml, anti Hib >=0.15ug/ml prior to booster administration.

Inclusion Criteria:

• Children, 18-24 months of age
• Subjects who had completed the primary series of Pentabio vaccine in the previous trial
• Father, mother, or legally acceptable representative have been informed properly regarding the study and signed the informed consent form
• Subject's parents commit to comply with the instruction

Exclusion Criteria:

• Subjects concomitantly enrolled or scheduled to be enrolled in another trial
• Evolving mild, moderate or severe illness, especially infectious diseases or fever (axillary temperature >=37.5oC on Day 0)
• Known history of uncontrolled coagulopathy or blood disorders contraindicating intramuscular injection
• Known history of allergy to any component of the vaccines (e.f. formaldehyde)
• Known history of acquired immunodeficiency (including HIV infection)
• Subject who has received a treatment likely to alter immune response in the previous 4 weeks (e.g intravenous immunoglobulin, blood-derived products or long term corticotherapy (>2 weeks)
• Subject receives other vaccination within 1 month prior to inclusion
• Any abnormality or chronic disease justified by investigator that might interfere assessment of the trial objectives
• Infant with a known history of diphtheria, tetanus, pertussis, Hepatitis B and Hib infection