So here's where the original study that got prevnar approved had some pneumonia data and 2 years after the vaccine has been approved based on this study (without this data included) 2 years after prevnar has been standard of care for the nation's infants.
In per protocol follow-up of children given PCV, first episodes of all clinically diagnosed pneumonia were reduced by 4.3% [95% confidence interval (CI), -3.5, 11.5%, P = 0.27]
That stuff after 4.3% says "we don't know when adjusting for random chance if the vaccine prevents all cause clinically diagnosed pneumonia or not. "
Then they go on to talk about how that number exploded to 17% as they continued the study. I'll get the original and see what's in there. This is only the abstract.
Of course there's other studies of the effectiveness and longer term effects on children ( see Invasive Pneumococcal Disease Caused by Nonvaccine Serotypes Among Alaska Native Children With High Levels of 7-Valent Pneumococcal Conjugate Vaccine Coverage)
Where the levels of IPD dropped 67% then rebounded with replacement serotypes with 19A being the most common. The overall rate of IPD was still lower at the end of this longer study but there was replacement disease and the serotype 19A has gone on to develop quite a reputation for causing multi-drug resistant infections in children.
But the original study in California got the stuff approved, so let's see what was going on down there.