In the eight states studied, 89 cases of invasive pneumococcal disease occurred before introduction and 57 occurred after introduction of the vaccine. With the introduction of the vaccine, the average rate of pneumococcal disease among young infants fell 40 %. The reduction was most pronounced for black infants. In case of white infants the decline was not statistically significant.
In conclusion the authors says that the pneumonia vaccine has resulted in herd immunity because neonates and young infants have had a significant decrease in pneumococcal disease rates, although they are too young to receive a full series of the vaccine.