Forty-seven selected stored samples from 37 children (23 infected, 14 uninfected, median age of 137
days) were examined. Plasma samples (volume 0.3–1.5 ml) were defrosted, centrifuged at 23,500×g at
4 ◦C for 60 min and determination of p24 was carried out in the resuspended pellet (0.12 ml).