Yderligere undersøgelser viste, at det var hensigtsmæssigt at indlede vaccinationen i seks- ugers - alderen, og at det var nødvendigt med en boosterdosis i det andet leveår for at vedligeholde beskyttelsen.
The additional studies showed that starting vaccination at six weeks was adequate, and that a booster dose is needed in the second year of life in order to maintain protection.