the conjugation process, however, offer the prospect of a more
affordable conjugate and should be pursued.10  There are a
number of specific scientific issues that must be considered as
conjugate vaccines continue along the development pipeline. For
instance, researchers need to determine how many pneumococcal
polysaccharide antigens can be incorporated into a single
vaccine using the same carrier proteins. They would also like to
know what sorts of immunization schedules and routes of
immunization will be most practical. Another important question
is whether more than one type of protein carrier can be combined
into one vaccine for several diseases (for example, Hib
glycoconjugate plus S. pneumoniae).  In the long term, however,
it is the complexity of making pneumococcal conjugates that
seems to pose the greatest challenge in the developing-world
context. A number of developing nations are now able to make DTP
reliably, and some are working collaboratively with developed-
world manufacturers to combine this