Sex-differential effect on infant mortality of oral polio vaccine administered with BCG at birth in Guinea-Bissau. A natural experiment.
BACKGROUND
The policy to provide oral polio vaccine (OPV) at birth was introduced in low-income countries to increase coverage. The effect of OPV at birth on overall child mortality was never studied. During a trial of vitamin A supplementation (VAS) at birth in Guinea-Bissau, OPV was not available during several periods. We took advantage of this "natural experiment" to test the effect on mortality of receiving OPV at birth.


METHODS
Between 2002 and 2004, the VAS trial randomised normal-birth-weight infants to 50,000 IU VAS or placebo administered with BCG. Provision of OPV at birth was not part of the trial, but we noted whether the infants received OPV or not. OPV was missing during several periods in 2004. We used Cox proportional hazards models to compute mortality rate ratios (MRR) of children who had received or not received OPV at birth.


RESULTS
A total of 962 (22.1%) of the 4345 enrolled children did not receive OPV at birth; 179 children died within the first year of life. Missing OPV at birth was associated with a tendency for decreased mortality (adjusted MRR = 0.69 (95% CI = 0.46-1.03)), the effect being similar among recipients of VAS and placebo. There was a highly significant interaction between OPV at birth and sex (p = 0.006). Not receiving OPV at birth was associated with a weak tendency for increased mortality in girls (1.14 (0.70-1.89)) but significantly decreased mortality in boys (0.35 (0.18-0.71)).


CONCLUSIONS
In our study OPV at birth had a sex-differential effect on mortality. Poliovirus is almost eradicated and OPV at birth contributes little to herd immunity. A randomised study of the effect of OPV at birth on overall mortality in both sexes is warranted.
Benn
Christine Stabell
CS
Bandim Health Project, Statens Serum Institut, Copenhagen, Denmark. cb@ssi.dk
Fisker
Ane Baerent
AB
Rodrigues
Amabelia
A
Ravn
Henrik
H
Sartono
Erliyani
E
Whittle
Hilton
H
Yazdanbakhsh
Maria
M
Aaby
Peter
P
D001500:BCG Vaccine / Q000627:therapeutic use*; D005260:Female; D006169:Guinea-Bissau; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D008297:Male; D011055:Poliovirus Vaccine, Oral / Q000009:adverse effects* / Q000627:therapeutic use*; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D012737:Sex Factors; D016896:Treatment Outcome; D014801:Vitamin A / Q000494:pharmacology; D014802:Vitamin A Deficiency / Q000188:drug therapy
D001500:BCG Vaccine; D011055:Poliovirus Vaccine, Oral; D014801:Vitamin A