Current challenges and development of polyvalent vaccines.

<p><b>(A)</b> Current potential challenges to development of polyvalent vaccine preparations. (<b>B</b>) Development and licensing of polyvalent vaccines in the United States. Combination vaccines are not reviewed here. Different colors indicate vaccines against the same pathogen. Blue, <i>Streptococcus pneumoniae</i> (polysaccharide vaccine and conjugate vaccine); red, poliovirus (inactivated vaccine and oral, live-attenuated vaccine); purple, <i>Neissaeria meningitides</i> (meningococcal vaccine: polysaccharide and conjugate vaccine); yellow, rotavirus (live attenuated); green, HPV, VLP; gray, adenovirus; white, influenza (inactivated and live-attenuated vaccines). Not all influenza vaccines are included. HPV, human papillomavirus; QC, quality control; VLP, viruslike particle.</p