Researchers investigated whether BCG revaccination at 19 months of age reduced child mortality. A randomised controlled trial was performed in Guinea-Bissau, west Africa. In total 1437 children were randomised to BCG revaccination and 1434 to no revaccination (controls). All trial participants had been vaccinated at birth and on the day of enrolment had low or no reactivity to tuberculin and were not severely sick. Children were followed from 19 months until 5 years of age. During follow-up 77 children died. The hazard ratio of death for the revaccinated children, compared with controls, was 1.2 (95% confidence interval 0.77 to 1.89).
Which of the following statements, if any, are true?
a) Revaccinated children had a 20% increased risk of death, compared with controls, at any time during follow-up.
b) The hazard rate for the revaccination group was assumed to be constant during follow-up.
c) Length of life of children in the control group was increased by 20%, compared with revaccinated children
d) It can be inferred that the hazard ratio of death for revaccinated children, compared with controls, will be 1.2 until the age of 10 years.
Answer a is true, while b, c, and d are false.