Even though vaccines are effective for prevention of diseases, compliance with recommended schedules of immunisation in early childhood is not always complete. Identification of potential risk factors associated with under-immunisation may help increase vaccination uptake. The objectives of this study were to determine the prevalence and risk factors of under-immunisation in hospitalised preschool children in Universiti Sains Malaysia Hospital (HUSM). Children aged 1 month to 2 years admitted between December 1998 and December 2000 in medical paediatric wards at HUSM were studied. Parents/guardians were interviewed during admission regarding immunisation status and potential risk factors. Children who did not have home-based cards during admission were excluded. Among 401 children, 37.9% had complete immunisation, 43.4% had delayed immunisation and 34.9% had incomplete immunisation. The uptake of BCG, DPT/OPV 1, DPT/OPV2, Hepatitis B3, DPT/OPV3, and measles were 98.5%, 90.7%, 83.2%, 81.4%,79.2% and 72.9% respectively. Vaccines scheduled to be given at later ages were significantly less likely to be taken (p=0.002) compared with vaccines scheduled to be given at an earlier age. Significant independent risk factors for under-immunisation were elderly mothers (3 40 years old) (OR 3.0, 95% CI: 1.2-8.0), low birth weight £2.0 kg (OR 6.2; 95% CI: 1.8-21.4) and presence of chronic illness in the child (OR 4.5; 95% CI: 2.5-7.9). In children whose father's education was low (primary school or no education), low maternal education was significantly associated with lower rate of under-immunisation (p = 0.005, OR 0.11 95%CI 0.02-0.51).
In conclusion this study showed that a large proportion of hospitalised preschool children were under-immunised, and vaccines scheduled to be given at a later age had lower uptakes. The situation can be rectified if every opportunity is taken to immunise all children, who have lapsed in their immunisation schedule.