Szilagyi PG, Griffin MR, Shone LP, Barth R, Zhu Y, Schaffer S, Ambrose S, Roy J, Poehling KA, Edwards KM, Walker FJ, Schwartz B. The impact of conjugate pneumococcal vaccination on routine childhood vaccination and primary care use in 2 counties. Pediatrics. 2006 Oct; 118(4):1394-402.