Dransfield MT, Nahm MH, Han MK, Harnden S, Criner GJ, Martinez FJ, Scanlon PD, Woodruff PG, Washko GR, Connett JE, Anthonisen NR, Bailey WC. Superior immune response to protein-conjugate versus free pneumococcal polysaccharide vaccine in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2009 Sep 15; 180(6):499-505.