"Original data reference:K. L. O'Brien, L. H. Moulton, R. Reid. Efficacy and safety of seven-valent conjugate pneumococcal vaccine in American Indian children: group randomised trial. Lancet 2003; 362: 355–361."
"Source: R. J. Hayes, L. H. Moulton. 2009. Cluster Randomised Trials. Chapman & Hall/CRC Boca Raton, FL."