Linder 2000.

Methods	Study design: open‐label, randomised trial Setting: Neonatal Division, Department of Pediatrics, Kalawati Saran Children's Hospital, Delhi, India Study dates: June to December 1994
Participants	Sample size: 177 infants (127 preterm infants and 50 full‐term infants) Dropouts/withdrawals: 40 children (22 = received blood products, 3 preterm infants = with sepsis, and 15 full‐term infants = withdrawn by their parents after the first blood test) Age: neonates (preterm experimental group median age = 32 weeks, full‐term control group = 40 weeks, preterm control group = 32 weeks) Sex: male = 62, female = 75 Inclusion criteria: preterm infants born between June and December 1994 (gestational age 30–35 weeks, weight > 1000 g); Fifty healthy full‐term infants (gestational age > 37 weeks, weight > 2500 g), born consecutively in the morning hours between 1 June 1994 and 15 June 1994. Exclusion criteria: not reported
Interventions	Preterm experimental? group (n = 50): II (I + O) O at birth, 2, 4 and 6 months Full‐term group (n = 50): I (I + O) O at 2, 4 and 6 months Preterm group (n = 52): I (I + O) O at 2, 4 and 6 months Fifty preterm infants received IPV intramuscularly within 24 hours of birth, in addition to routine recommended childhood immunisations. Fifty‐two preterm infants and 35 full‐term infants received routine immunisations only (routine vaccination timing: HBV at birth, 1 and 6 months of age; IPV at 2 and 4 months; oral polio vaccine (OPV) at 4 and 6 months; diphtheria‐tetanus‐ pertussis (DTP) at 2, 4, and 6 months; and Haemophilus influenzae B vaccine at 2 and 4 months). Blood samples were taken at birth, 3 and 7 months of age from all infants, and at 1 month of age from preterm infants only.
Outcomes	Geometric mean titre of serum polio neutralising antibodies at 7 months Protective humoral response at 7 months Timing of outcome assessment: 7 months Follow‐up: 7 months
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The preterm infants were divided into a study group (group A; n = 50) and a control group (group B; n = 52) by 1:1 randomisation..." Comment: probably done properly, since the table of baseline characteristics of randomised participants is balanced
Allocation concealment (selection bias)	Low risk	Quote: "...using a blinded envelope drawn by the parents. All full term infants were included in control group C."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Comment: no blinding but performance is not likely to be influenced by lack of blinding in terms of intervention or co‐interventions
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Comment: no blinding but the objective outcome (antibody titres) is not likely to be influenced by lack of blinding
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: no lost to follow‐up. At the bottom of Table 5 "A, group A (n = 50); B, group B (n = 52); C, group C (n = 35)" (quote)
Selective reporting (reporting bias)	Low risk	Comment: no evidence of selecting reporting
Other bias	Low risk	Comment: no evidence of other bias
Conflict of interest	Low risk	Comment: this study was supported by the chief scientist of the Israel Ministry of Health.