FIGURE 2.

Effect of neonatal immunization on the first dose administered during the infancy. The infant doses were administered in both immunized or non-immunized mice at 21 days during the neonatal period in either the presence or the absence of a neonatal dose at 7 days of age. In the neonates immunized (upper indications on the abscissa), the type of vaccine used was the same as that administered during infancy (lower indications on the abscissa). The non-immunized mice were used as a negative control of protection. All the groups of mice (n = 8) were challenged with B. pertussis at 35 days after birth. The number of bacteria recovered from mouse lungs, expressed as the log₁₀(CFUs per lung), is plotted on the ordinate for the type and vaccine schedule indicated on the abscissa, with the data representing the means ± the SD. The dotted horizontal line indicates the lower limit of detection. ^∗∗∗p < 0.001, ^∗∗p < 0.05.