To the Editor: The article by Broome et al. in the September 4 issue demonstrates a novel approach to assessing the efficacy of the 14-valent pneumococcal vaccine in the absence of denominators of vaccinated and unvaccinated populations. Unfortunately, the mathematical approach to assessing efficacy, though accurate, is too complex to be understood by most physicians. It could be rephrased in simple, logical terms, as follows. Because it is documented that vaccinated and unvaccinated populations are infected with nonvaccine pneumococcal disease at similar rates (Table 2 of Broome), it is reasonable to assume that, if the vaccine is ineffective, the proportion. . .
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